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may 13, 2004 1 m9999-051304 micrf505 micrel micrf505 868mhz and 915mhz ism band transceiver general description the micrf505 is a true single chip, frequency shift keying (fsk) transceiver intended for use in half-duplex, bidirec- tional rf links. the multi-channeled fsk transceiver is intended for uhf radio equipment in compliance with the north american federal communications commission (fcc) part 15.247 and 249, as well as the european telecommuni- cation standard institute (etsi) specification, en300 220. the transmitter consists of a pll frequency synthesizer and a power amplifier. the frequency synthesizer consists of a voltage-controlled oscillator (vco), a crystal oscillator, dual modulus prescaler, programmable frequency dividers, and a phase-detector. the loop-filter is external for flexibility and can be a simple passive circuit. the output power of the power amplifier can be programmed to seven levels. a lock- detect circuit detects when the pll is in lock. in receive mode, the pll synthesizer generates the local oscillator (lo) signal. the n, m , and a values that give the lo frequency are stored in the n0, m0, and a0 registers. the receiver is a zero intermediate frequency (if) type which makes channel filtering possible with low-power, integrated low-pass filters. the receiver consists of a low noise amplifier (lna) that drives a quadrature mixer pair. the mixer outputs feed two identical signal channels in phase quadrature. each channel includes a pre-amplifier, a third order sallen-key rc low-pass filter that protects the following switched-capacitor filter from strong adjacent channel signals, and a limiter. the main channel filter is a switched-capacitor implementation of a six-pole elliptic low pass filter. the cut-off frequency of the sallen-key rc filter can be programmed to four different frequencies: 100khz, 150khz, 230khz, and 340khz. the i and q channel outputs are demodulated and produce a digital data output. the demodulator detects the relative phase of the i and the q channel signal. if the i channel signal lags behind the q channel, the fsk tone frequency is above the lo frequency (data ?1?). if the i channel leads the q channel, the fsk tone is below the lo frequency (data ?0?). the output of the receiver is available on the dataixo pin. a receive signal strength indicator (rssi) circuit indicates the received signal level. all support documentation can be found on micrel?s web site at www.micrel.com. features ? true single chip transceiver ? digital bit synchronizer ? received signal strength indicator (rssi) ? rx and tx power management ? power down function ? reference crystal tuning capabilities ? baseband shaping ? three-wire programmable serial interface ? register read back function applications ? telemetry ? remote metering ? wireless controller ? remote data repeater ? remote control systems ? wireless modem ? wireless security system ordering information part number junction temp. range package MICRF505BML ?40 c to +85 c 32-pin mlf? micrel, inc. ? 1849 fortune drive ? san jose, ca 95131 ? usa ? tel + 1 (408) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.mic rel.com micro leadframe and mlf are trademarks of amkor technology, inc.
micrf505 micrel m9999-051304 2 may 13, 2004 typical application
may 13, 2004 3 m9999-051304 micrf505 micrel pin configuration 32-pin mlf? pin description pin number pin name type pin function 1 rfgnd lna and pa ground. 2 ptatbias o connection for bias resistor. 3 rfvdd lna and pa power supply. 4 rfgnd lna and pa ground. 5 ant i/o antenna in/output 6 rfgnd lna and pa ground. 7 rfgnd lna and pa ground. 8 nc no connect. 9 cibias o connection for bias resistor. 10 ifvdd if/mixer power supply. 11 ifgnd if/mixer ground. 12 ichout o test pin. 13 qchout o test pin. 14 rssi o received signal strength indicator. 15 ld o pll lock detect. 16 nc no connect. 17 nc no connect. 18 dataclk o rx/tx data clock output. 19 dataixo i/o rx/tx data input/output. 20 io i/o 3-wire interface data in/output 21 sclk i 3-wire interface serial clock. 22 cs i 3-wire interface chip select. 23 xtalin i crystal oscillator input. 24 xtalout o crystal oscillator output. 25 digvdd digital power supply. 26 diggnd digital ground. 27 cpout o pll charge pump output. 28 gnd substrate ground. 29 varin i vco varactor input. 30 vcognd vco ground. 31 vcovdd vco power supply. 32 nc no connect. 1 2 3 4 5 6 7 8 24 23 22 21 20 19 18 17 9 10111213141516 32 3130 29 28 27 26 25 micrf505 32-pin mlf rfgnd pta rfvdd rfgnd ant rfgnd gnd nc xtalout xtalin cs sclk io dataixo dataclk nc gnd varin vcognd vcovd nc cpout diggnd digvdd qchout ichout ifgnd ifvdd cibias rssi ld nc
micrf505 micrel m9999-051304 4 may 13, 2004 absolute maximum ratings (1) supply voltage (v dd ) ................................................. +3.3v voltage on any pin (gnd = 0v) ................. ?0.3v to 2.7v lead temperature (soldering, 4 sec.) ...................... tbd c storage temperature (t s ) ....................... ?55 c to +150 c esd rating (3) ............................................................................... 2kv operating ratings (2) supply voltage (v in ) ................................... +2.0v to +2.5v rf frequencies ................................... 850mhz to 950mhz data rate (nrz) .............................................. < 200kbaud ambient temperature (t a ) ......................... ?40 c to +85 c package thermal resistance mlf? (q ja ) multi-layer board .......................... 41.7 c/w electrical characteristics (4) f rf = 915mhz, data-rate = 125kbps, modulation type = closed-loop vco modulation, v dd = 2.5v; t a = 25 c, bold values indicate ?40 c t a +85 c; unless noted. symbol parameter condition min typ max units rf frequency operating range 850 950 mhz power supply 2.0 2.5 v power down current 0.3 m a standby current 280 m a vco and pll section reference frequency 440 mhz pll lock time 915mhz to 915.5mhz 0.5 ms 3khz bandwidth 902mhz to 927mhz 1.7 ms 20khz bandwidth 0.3 ms switch time rx ? tx 0.6 ms 3khz loop bandwidth tx ? rx 0.6 ms standby rx 1.1 ms standby tx 1.2 ms crystal oscillator start-up time 16mhz, 9pf load, 5.6pf loading capacitors 1.2 ms charge pump current vcp out = 1.1v, cp_hi = 0 125 m a vcp out = 1.1v, cp_hi = 1 500 m a charge pump tolerance 20 % transmit section output power r load = 50 w , pa2-0-111 10 dbm r load = 50 w , pa2-0-001 ?8 dbm output power tolerance over temperature range 2 db over power supply range 3 db tx current consumption r load = 50 w , pa2-0-111 28 ma r load = 50 w , pa2-0-001 14 ma tx current consumption variation 10dbm 2.5 ma binary fsk frequency separation (5) bitrate = 200kbps 20 500 khz data rate (5) vco modulation 20 200 kbps occupid bandwidth 20kbps, b = 2, 20dbc khz 125kbps, b = 2, 20dbc khz 200kbps, b = 2, 20dbc khz 2nd harmonic ?25 dbm 3rd harmonic ?15 dbm spurious emission < 1ghz (5) < ?54 dbm spurious emission < 1ghz (5) < ?30 dbm
may 13, 2004 5 m9999-051304 micrf505 micrel symbol parameter condition min typ max units receive section rx current consumption 13.5 ma lna bypass 11.5 ma switch cap filter bypass with lna 11.5 ma rx current consumption variation over temperature 4 ma receiver sensitivity 2.4kbps, b = 16 ?111 dbm 4.8kbps, b = 16 ?109 dbm 19.2kbps, b = 4 ?105 dbm 38.4kbps, b = 4 ?103 dbm 76.8kbps, b = 2 ?101 dbm 125kbps, b = 2 ?99 dbm 200kbps, b = 2 ?97 dbm receiver maximum input power 125kbps, 125khz deviation ?12 dbm 20kbps, 20khz deviation ?20 dbm receiver sensitivity tolerance over temperature 4 db over power supply range 1 db receiver bandwidth 50 340 khz co-channel rejection db adjacent channel rejection 200khz spacing 500khz spacing 1mhz spacing blocking 1mhz 42 db 2mhz 47 db 5mhz 38 db 10mhz 41 db noise figure, cascade tbd db 1db compression ?35 db input ip3 2 tones with 1mhz separation ?25 dbm input ip2 dbm lo leakage ?90 dbm spurious emission < 1ghz ?54 dbm > 1ghz ?54 dbm input impedance (5) ~50 w input reflection (s11) (5) ?20 ?15 db rssi dynamic range 50 db rssi output voltage pin = 100dbm 0.9 v pin = 60dbm 1.85 v
micrf505 micrel m9999-051304 6 may 13, 2004 symbol parameter condition min typ max units digital inputs/outputs v ih logic input high 0.7v dd v dd v v il logic input low 0 0.3v dd v clock/data frequency (5) 10 mhz clock/data duty cycle (5) 45 55 % notes: 1. exceeding the absolute maximum ratings may damage the device. 2. the device is not guaranteed to function outside its operating ratings. 3. devices are esd sensitive. handling precautions recommended. human body model, 1.5k in series with 100pf. 4. specification for packaged product only. 5. guaranteed by design.
may 13, 2004 7 m9999-051304 micrf505 micrel programming general the micrf505 functions are enabled through a number of programming bits. the programming bits are organized as a set of addressable control registers, each register holding 8 bits. there are 23 control registers in total in the micrf505, and they have addresses ranging from 0 to 22. the user can read all the control registers. the user can write to the first 22 registers (0 to 21); the register with address 22 is a read-only register. all control registers hold 8 bits and all 8 bits must be written to when accessing a control register, or they will be read. some of the registers do not utilize all 8 bits. the value of an unused bit is ?don?t care.? the control register with address 0 is referred to as controlregister0, the control register with address 1 is controlregister1 and so on. a summary of the control regis- ters is given in the table below. in addition to the unused bits (marked with ?-?) there are a number of fixed bits (marked with ?0? or ?1?). always maintain these as shown in the table. the control registers in micrf505 are accessed through a 3- wire interface; clock, data and chip select. these lines are referred to as sclk, io, and cs, respectively. this 3-wire interface is dedicated to control register access and is re- ferred to as the control interface. received data (via rf) and data to transmit (via rf) are handled by the dataixo and dataclk (if enabled) lines; this is referred to as the data interface. the sclk line is applied externally; access to the control registers are carried out at a rate determined by the user. the micrf505 will ignore transitions on the sclk line if the cs line is inactive. the micrf505 can be put on a bus, sharing clock and data lines with other devices. all control registers should be initiated (written to) following a power-on. during operation, however, writing to one register is sufficient to change the way the transceiver works.
micrf505 micrel m9999-051304 8 may 13, 2004 adr data a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000000 lna_by pa2 pa1 pa0 sync_en mode1 mode0 load_en 0000001 modulation1 modulation0 ?0? ?0? rssi_en ld_en pf_fc1 pf_fc0 0000010 cp_hi ?0? ?0? ?0? outs3 outs2 outs1 outs0 0000011 ?1? ?1? ?0? vco_ib2 vco_ib1 vco_ib0 vco_freq1 vco_freq0 0000100 mod_f2 mod_f1 mod_f0 mod_i4 mod_i3 mod_i2 mod_i1 mod_i0 0000101 - - ?0? ?1? mod_a3 mod_a2 mod_a1 mod_a0 0000110 - mod_clks2 mod_clks1 mod_clks0 bitsync_clks2 bitsync_clks1 bitsync_clks0 bitrate_clks2 0000111 bitrate_clks1 bitrate_clks0 refclk_k5 refclk_k4 refclk_k3 refclk_k2 refclk_k1 refclk_k0 0001000 ?1? scclk_x2 scclk5 scclk4 scclk3 scclk2 scclk1 scclk0 0001001 ?0? ?0? ?1? xcotune4 xcotune3 xcotune2 xcotune1 xcotune0 0001010 - - a0_5 a0_4 a0_3 a0_2 a0_1 a0_0 0001011 ---- n0_11 n0_10 n0_9 n0_8 0001100 n0_7 n0_6 n0_5 n0_4 n0_3 n0_2 n0_1 n0_0 0001101 ---- m0_11 m0_10 m0_9 m0_8 0001110 m0_7 m0_6 m0_5 m0_4 m0_3 m0_2 m0_1 m0_0 0001111 - - a1_5 a1_4 a1_3 a1_2 a1_1 a1_0 0010000 ---- n1_11 n1_10 n1_9 n1_8 0010001 n1_7 n1_6 n1_5 n1_4 n1_3 n1_2 n1_1 n1_0 0010010 ---- m1_11 m1_10 m1_9 m1_8 0010011 m1_7 m1_6 m1_5 m1_4 m1_3 m1_2 m1_1 m1_0 0010100 ?1? ?0? ?1? ?1? ?0? ?1? ?0? ?1? 0010101 ---- feec_3 feec_2 feec_1 feec_0 0010110 fee_7 fee_6 fee_5 fee_4 fee_3 fee_2 fee_1 fee_0 table 1. control registers in micrf505 names of programming bits, unused bits (?-?) and fixed bits (?1? or ?0?) are shown. the control register with address 0 is refe rred to as controlregister0 etc. writing to the control registers in micrf505 writing: a number of octets are entered into micrf505 followed by a load-signal to activate the new setting. making these events is referred to as a ?write sequence.? it is possible to update all, 1, or n control registers in a write sequence. the address to write to (or the first address to write to) can be any valid address (0-21). the io line is always an input to the micrf505 (output from user) when writing. what to write: ? the address of the control register to write to (or if more than 1 control register should be written to, the address of the 1st control register to write to) ? a bit to enable reading or writing of the control registers. this bit is called the r/w bit. ? the values to write into the control register(s) field comments address: a 7 bit field, ranging from 0 to 21. msb is written first. r/w bit: a 1-bit field, = ?0? for writing values: a number of octetes (1-22 octetes). msb in every octet is written first. the first octet is written to the control regis ter with the specified address (="adress"). the next octet (if there is one) is writtento the control register with address= "adress + 1" and so on. table 2.
may 13, 2004 9 m9999-051304 micrf505 micrel how to write: bring cs active to start a write sequence. the active state of the cs line is ?high.? use the sclk/io serial interface to clock ?address? and ?r/w bit and ?values? into the micrf505. micrf505 will sample the io line at negative edges of sclk. make sure to change the state of the io line before the negative edge. refer to figures below. bring cs inactive to make an internal load-signal and com- plete the write-sequence. note: there is an exception to this point. if the programming bit called ?load_en? (bit0 in controlregister0) is ?0?, then no load pulse is generated. the two different ways to ?program the chip? are: ? write to a number of control registers (0-22) when the registers have incremental addresses (write to 1, all, or n registers) ? write to a number of control registers when the registers have non-incremental addresses writing to a single register writing to a control register with address ?a6, a5, ... a0? is described here. during operation, writing to 1 register is sufficient to change the way the transceiver works. typical example: change from receive mode to power-down. field comments address: 7 bit = a6, a5, ... a0 (a6 = msb, a0 = lsb) r/w bit: ?0? for writing values: 8 bits = d7, d6, ... d0 (d7 = msb, d0 = lsb) table 3. ?address? and ?r/w bit? together make 1 octet. in addition, 1 octet with programming bits is entered. totally, 2 octets are clocked into the micrf505. d0 d1 d2 d6 d7 rw a0 a5 a6 cs sclk io address of register i rw data to write into register i internal load pulse made here figure 1. in figure 1, io is changed at positive edges of sclk. the micrf505 samples the io line at negative edges. the value of the r/w bit is always ?0? for writing. writing to all registers after a power-on, all writable registers should be written. this is described here. writing to all registers can be done at any time. to get the simplest firmware, always write to all registers. the price to pay for the simplicity is increased write-time, which leads to increased time to change the way the micrf505 works. what to write field comments address: '0000000' (address of the first register to write to, which is 0) r/w bit: ?0? for writing values: 1st octet: wanted values for controlregister0. 2nd octet: wanted values for controlregister1 and so on for all of the octets. so the 22nd octet wants values for controlregister21. refer to the specific sections of this document for actual values. table 4. address and r/w bit together make 1 octet. in addition, 22 octets with programming bits are entered. totally, 23 octets are clocked into the micrf505. how to write: ? bring cs high ? use sclk and io to clock in the 2 octets ? bring cs low
micrf505 micrel m9999-051304 10 may 13, 2004 how to write: ? bring cs high ? use sclk and io to clock in the 23 octets ? bring cs low refer to the figure in the next section, ?writing to n registers having incremental addresses?. writing to n registers having incremental addresses in addition to entering all bytes, it is also possible to enter a set of n bytes, starting from address i = ?a6, a5, ... a0.? typical example: clock in a new set of frequency dividers (i.e. change the rf frequency). ?incremental addresses?: registers to be written are located in i, i+1, i+2 ... what to write field comments address: 7 bit = a6, a5, ... a0 (a6 = msb, a0 = lsb) (address of first byte to write to) r/w bit: ?0? for writing values: n* 8 bits = d7, d6, ... d0 (d7 = msb, d0 = lsb) (written to control reg. with address ?i?) d7, d6, ... d0 (d7 = msb, d0 = lsb) (written to control reg. with address ?i+1?) ... d7, d6, ... d0 (d7 = msb, d0 = lsb) (written to control reg. with address ?i+n-1 ?) table 5. ?address? and ?r/w bit? together make 1 octet. in addition, n octets with programming bits are entered. totally, 1 + n octets are clocked into the micrf505. how to write: ? bring cs high ? use sclk and io to clock in the 1 + n octets ? bring cs low in figure 1, n = 2 (write to 2 registers in the micrf505). in the figure, io is changed at positive edges of sclk. the micrf505 samples the io line at negative edges. the value of the r/w bit is always ?0? for writing. figure 2. d0 d7 d0 d7 rw a0 a5 a6 cs sclk io address of first register to write to, register i rw data to write into register i internal load pulse made here data to write into register i+1
may 13, 2004 11 m9999-051304 micrf505 micrel writing to n registers having non- incremental addresses registers with non-incremental addresses can be written to in one write-sequence as well. example of non-incremental addresses: ?0,1,3?. however, this requires more overhead, and the user should consider the possibility to make a ?continuous? update, for example, by writing to ?0,1,2,3? (writing the present value of ?2? into ?2?). the simplest firmware is achieved by always writing to all registers. refer to previous sections. this write-sequence is divided into several sub-parts: ? disable the generation of load-signals by clearing bit ?load_en? (bit0 in controlregister0) ? repeat for each group of registers having incre- mental addresses: ? bring cs active ? enter first address for this group, r/w bit and values ? bring cs inactive ? finally, enable and make a load-signal by setting ?load_en? refer to the previous sections for how to write to 1 or n (with incremental addresses) registers in the micrf505. reading from the control registers in micrf505 the ?read-sequence? is: 1. enter address and r/w bit 2. change direction of io line 3. read out a number of octets and change io direction back again. it is possible to read all, 1 or n registers. the address to read from (or the first address to read from) can be any valid address (0-22). reading is not destructive, i.e. values are not changed. the io line is output from the micrf505 (input to user) for a part of the read-sequence. refer to procedure description below. a read-sequence is described for reading n registers, where n is a number 1-23. reading n registers from micrf505 figure 3. in the figure, 1 register is read. the address is a6, a5, ... a0. a6=msb. the data read out is d7, d6, ... d0. the value of the r/w bit is always ?1? for reading. sclk and io together form a serial interface. sclk is applied externally for reading as well as for writing. ? bring cs active ? enter address to read from (or the first address to read from) (7 bits) and ? the r/w bit = 1 to enable reading ? make the io line an input to the user (set pin in tristate) ? read n octets. the first rising edge of sclk will set the io as an output from the micrf505. micrf will change the io line at positive edges. the user should read the io line at the negative edges. ? bring cs inactive. this will make the io line an input to the micrf505 again ? make the io line an output from the user again. sclk cs io a 6 a5 rw d7 d6 d0 a0 address of register i data read fromreg. i rw io input io output sample time
micrf505 micrel m9999-051304 12 may 13, 2004 programming interface timing figure 4 and table 6 shows the timing specification for the 3-wire serial programming interface. figure 4. values symbol parameter min. typ. max. units tper min. period of sclk 50 ns thigh min. high time of sclk 20 ns tlow min. low time of slck 20 ns tfall max. time of falling edge of slck 1 m s trise max. time of rising edge of slck 1 m s tcsr min. delay from rising edge of cs to falling edge of sclk 0 ns tcsf min. delay from falling edge of cs to rising edge of sclk 5 ns twrite min. delay from valid io to falling edge of sclk during a write operation 0 ns tread min. delay from rising edge of sclk to valid io during a read operation (assuming load capacitance of io is 25 pf) 75 ns programming summary ? use cs, sclk, and io to get access to the control registers in micrf505. ? sclk is user-controlled. ? write to the micrf505 at positive edges (micrf 505 reads at negative edges). ? read from the micrf505 at negative edges (micrf505 writes at positive edges). ? after power-on: write to the complete set of control registers ? address field is 7 bits long. enter msb first ? r/w bit is 1 bit long (?1? for read, ?0? for write) ? address and r/w bit together make 1 octet ? all control registers are 8 bits long. enter/read msb in every octet first ? always write 8 bits to/read 8 bits from a control register. this is the case for registers with less than 8 used programming bits as well. ? writing: bring cs high, write address and r/w bit followed by the new values to fill into the addressed control register(s) and bring cs low for loading, i.e. activation of the new control register values (?load_en? = 1). ? reading: bring cs high, write address and r/w bit, set io as an input, read present contents of the addressed control register(s), bring cs low and set io as an output. sclk cs io a6 a5 rw d7 d6 d0 d1 d2 a0 trise tfall tper tcsr address register data register load tcsl tlow thightread twrite table 6. timing specification for the 3-wire programming interface
may 13, 2004 13 m9999-051304 micrf505 micrel frequency synthesizer a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0001010 - - a0_5 a0_4 a0_3 a0_2 a0_1 a0_0 0001011 - - - - n0_11 n0_10 n0_9 n0_8 0001100 n0_7 n0_6 n0_5 n0_4 n0_3 n0_2 n0_1 n0_0 0001101 - - - - m0_11 m0_10 m0_9 m0_8 0001110 m0_7 m0_6 m0_5 m0_4 m0_3 m0_2 m0_1 m0_0 0001111 - - a1_5 a1_4 a1_3 a1_2 a1_1 a1_0 0010000 - - - - n1_11 n1_10 n1_9 n1_8 0010001 n1_7 n1_6 n1_5 n1_4 n1_3 n1_2 n1_1 n1_0 0010010 - - - - m1_11 m1_10 m1_9 m1_8 0010011 m1_7 m1_6 m1_5 m1_4 m1_3 m1_2 m1_1 m1_0 the frequency synthesizer consists of a voltage-controlled oscillator (vco), a crystal oscillator, dual modulus prescaler, programmable frequency dividers and a phase-detector. the loop-filter is external for flexibility and can be a simple passive circuit. the lengths of the n and m and a registers are 12, 12 and 6 bits respectively. the m, n and a values can be calculated from the formula: where phd is the phase detector comparison frequency. phd: phase detector comparison frequency fxco: crystal oscillator frequency fvco: voltage controlled oscillator frequency there are two sets of each of the divide factors (i.e. a0 and a1). if modulation by using the dividers is selected (that is modulation1=1, modulation0=0), the two sets should be programmed to give two rf frequencies, separated by two times the specified frequency deviation. for all other modulation methods, and also in receive mode, the 0-set will be used. crystal oscillator (xco) a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0001001 ?0? ?0? ?1? xcotune4 xcotune3 xcotune2 xcotune1 xcotune0 the crystal oscillator is a very critical block. as the crystal oscillator is a reference for the rf output frequency and also for the lo frequency in the receiver, very good phase and frequency stability is required. the schematic of the crystal oscillator?s external components for 16mhz are shown in figure 2. c11 5.6pf c10 5.6pf y1 tsx-10a pin 24 xtalout pin 23 xtalin figure 5. crystal oscillator circuit the crystal should be connected between pins xoscin and xoscout (pin 23 and 24). in addition, loading capacitors for the crystal are required. the loading capacitor values depend on the total load capacitance, c l , specified for the crystal. the load capacitance seen between the crystal terminals should be equal to c l for the crystal to oscillate at the specified frequency. f f m f 16 n a f 16 n a phd xco vco / 2 rf == + = +
micrf505 micrel m9999-051304 14 may 13, 2004 c 1 1 c 1 c c l 10 11 parasitic = + + the parasitic capacitance is the pin input capacitance and pcb stray capacitance. typically the total parasitic capaci- tance is around 6pf. for instance, for a 9pf load crystal the recommended values of the external load capacitors are 5.6pf. it is also possible to tune the crystal oscillator internally by switching in internal capacitance using 5 tune bits xcotune4 - xcotune0. when xcotune4 - xcotune0 = 0 no internal capacitors are connected to the crystal pins. when xcotune4 - xcotune0 = 1 all of the internal capacitors are connected to the crystal pins. figure 3 shows the tuning range for two different capacitor values, these are 1.5pf and no capacitors. the crystal used is a tn4-26011 from toyocom. specifica- tion: package tsx-10a, nominal frequency 16.000000 mhz, frequency tolerance 10ppm, frequency stability 9ppm, load capacitance 9pf, pulling sensitivity 15ppm/pf. -60,0 -40,0 -20,0 0,0 20,0 40,0 60,0 80,0 100,0 0 8 16 24 32 xco bitvalue [ppm] 2x1.5pf 2x0pf figure 6. xco tuning the start up time is given in table 7. as can be seen, more capacitance will slow down the start up time. the start-up time of a crystal oscillator is typically around a millisecond. therefore, to save current consumption, the xco is turned on before any other circuit block. during start- up the xco amplitude will eventually reach a sufficient level to trigger the m-counter. after counting 2 m-counter output pulses the rest of the circuit will be turned on. the current consumption during the prestart period is approximately 280 m a. xco bitvalue start-up time (ms) 0 590 1 590 2 700 4 700 8 810 16 1140 31 2050 table 7. typical values with c ext = 1.5pf if an external reference shall be used instead of a crystal, the signal shall be applied to pin 24, xtalout. due to internal dc setting in the xco, an ac coupling is recommended to be used between the external reference and the xtalout-pin. vco a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000011 ?1? ?1? ?0? vco_ib2 vco_ib1 vco_ib0 vco_freq1 vco_freq0 the vco has no external components. it has three bit to set the bias current and two bit to set the vco frequency. these five bit are set by the rf frequency, as follows: rf freq. vco_ib2 vco_ib1 vco_ib0 vco_freq1 vco_freq0 850mhz 1110 0 868mhz 0110 1 915mhz 0011 0 950mhz 0001 1 table 8. vco bit setting the bias bit will optimize the phase noise, and the frequency bit will control a capacitor bank in the vco. the tuning range, the rf frequency versus varactor voltage, is dependent on the vco frequency setting, and can be shown in figure 4. when the tuning voltage is in the range from 0.9v to 1.4v, the vco gain is at its maximum, approximately 65 to 70mhz/v. it is recommended that the varactor voltage stays in this range. the input capacitance at the varactor pin must be taken into considerations when designing the pll loop filter. this is most critical when designing a loop filter with high bandwidth, which gives relatively small component values. the input capacitance is approximately 6pf. tuning range 800 820 840 860 880 900 920 940 960 980 1000 0 0,5 1 1,5 2 2,5 varactor voltage (v) '00' '01' '10' '11' figure 7. rf frequency vs. varactor voltage and vco frequency bit (v dd = 2.25v)
may 13, 2004 15 m9999-051304 micrf505 micrel charge pump a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000011 cp_hi ?0? ?0? ?0? outs3 outs2 outs1 outs0 the charge pump current can be set to either 125 m a or 500 m a by cp_hi (?1? d 500 m a). this will affect the loop filter compo- nent values, see ?pll filter? section. in most cases, the lowest current is best suited. for applications using a high phase detector frequency and a high pll bandwidth, the 500 m a can be a better choice. pll filter the design of the pll filter will strongly affect the perfor- mance of the frequency synthesizer. the pll filter is kept externally for flexibility. input parameters when designing the loop filter for the micrf505 are mainly the modulation method and the bit rate. these choices will also affect the switching time and phase noise. the frequency modulation can be done in two different ways with the micrf505, either by vco modulation or by modu- lation with the internal dividers (see chapter frequency modulation for further details). in the first case, the pll bandwidth needs to be adequately low not to cancel the modulation. in the second case, using the dividers, the pll needs to lock on a new carrier frequency for every new data bit. now the pll bandwidth needs to be adequately high. it may be necessary to use a third order filter to suppress the phase detector frequency, as this is not suppressed as much as when doing modulation on the vco. a schematic for a second and third order loop filter is shown in figure 5. for a second order filter, c3 is not connected and r2 is 0 w . c3 c1 pin 27 cp_out pin 29 varin c2 r2 r1 figure 8. second and third order loop filter table 9 shows three different loop filters, the two first for vco modulation and the last one for modulation using the internal dividers. the component values are calculated with rf frequency = 915mhz, vco gain = 67mhz/v and charge pump current = 125 m a. other settings are shown in the table. the varactor pin capacitance (pin 29) of 6pf does not influence on the component values for the two filters with lowest bandwidth. for the 12khz bandwidth filter, a third order loop filter is calculated. the third pole is set by r2 c3. here c3 is chosen to be 6pf, the same as the varactor input pin capacitance (pin 29). c3 can therefore be skipped. baud rate pll bw phase phase (kbaud/sec) (khz) margin ( ) detector freq. (khz) c1 c2 r1 r2 c3 vco >20 0.8 56 500 56nf 560nf 1.2k w 0nc vco >125 3 56 500 3.9nf 560nf 4.7k w 0nc internal >10 12 65 300 56nf 560pf 27k w 220k w nc table 9. loop filter components values
micrf505 micrel m9999-051304 16 may 13, 2004 lock detect a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000001 modulation1 modulation0 "0" "0" rssi_en ld_en pf_fc1 pf_fc0 a lock detector can be enabled by setting ld_en = 1. when pin ld is high, it indicates that the pll is in lock. modes of operation a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000000 lna_by pa2 pa1 pa0 sync_en mode1 mode0 load_en mode1 mode0 state comments 0 0 power down keeps register configuration 0 1 standby only crystal oscillator running 1 0 receive full receive 1 1 transmit full transmit ex pa stage transceiver sync/non-synchronous mode a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000000 lna_by pa2 pa1 pa0 sync_en mode1 mode0 load_en 0000110 ? mod_clks2 mod_clks1 mod_clks0 bitsync_clks2 bitsync_clks1 bitsync_clks0 bitrate_clks2 0000111 bitrate_clks1 bitrate_clks0 refclk_k5 refclk_k4 refclk_k3 refclk_k2 refclk_k1 refclk_k0 sync_en state comments 0 rx: bit synchronization off transparent reception of data 0 tx: dataclk pin off transparent transmission of data 1 rx: bit synchronization on bit-clock is generated by transceiver 1 tx: dataclk pin on bit-clock is generated by transceiver when sync_en = 1, it will enable the bit synchronizer in receive mode. the bit synchronizer clock needs to be pro- grammed, see chapter bit synchronizer. the synchronized clock will be set out on pin dataclk. in transmit mode, when sync_en = 1, the clock signal on pin dataclk is a programmed bit rate clock. now the transceiver controls the actual bit rate. the data to be transmitted will be sampled on rising edge of dataclk. the micro controller can therefore use the negative edge to change the data to be transmitted. the clock used for this purpose, bitrate-clock, is programmed in the same way as the modulator clock and the bit synchronizer clock: f f refclk_k 2 bitrate_clk xco = - () 7 bitrate clks _ where: fbitrate_clk: the clock frequency used to control the bit rate, should be equal to the bit rate (a bit rate of 20 kbit/sec requires a clock frequency of 20khz) fxco: crystal oscillator frequency refclk_k: 6 bit divider, values between 1 and 63 bitrate_clks: bit rate setting, values between 0 and 6
may 13, 2004 17 m9999-051304 micrf505 micrel data interface the micrf505 interface can be divided in to two separate interfaces, a ?programming interface? and a ?data interface?. the ?programming interface? has a three wire serial program- mable interface and is described in chapter programming. the ?data interface? can be programmed to sync-/non-syn- chronous mode. in synchronous mode the micrf505 is defined as ?master? and provides a data clock that allows users to utilize low cost micro controller reference frequency. the data interface is defined in such a way that all user actions should take place on falling edge and is illustrated figure 6 and 7. the two figures illustrate the relationship between dataclk and dataixo in receive mode and transmit mode. micrf505 will present data on rising edge and the ?user? sample data on falling edge in receive mode. dataixo dataclk figure 9. data interface in receive mode the user presents data on falling edge and micrf505 samples on rising edge in transmit mode. dataixo dataclk figure 10. data interface in transmit mode when entering transmit mode it is important to keep dataixo in tri-state from the time tx-mode is entered until user starts sending data. the data is provided directly to the modulation circuit and violation of this may/will cause abnormal behavior. depending on the chosen fsk modulation some sort of encoding might be needed. the different modulation types and encoding is described in chapter frequency modulation. receiver the receiver is a zero intermediate frequency (if) type in order to make channel filtering possible with low-power integrated low-pass filters. the receiver consists of a low noise amplifier (lna) that drives a quadrature mixer pair. the mixer outputs feed two identical signal channels in phase quadrature. each channel include a pre-amplifier, a third order sallen-key rc lowpass filter that protects the following switched-capacitior filter from strong adjacent channel sig- nals and finally a limiter. the main channel filter is a switched- capacitor implementation of a six-pole elliptic lowpass filter. the elliptic filter minimizes the total capacitance required for a given selectivity and dynamic range. the cut-off frequency of the sallen-key rc filter can be programmed to four different frequencies: 100khz, 150khz, 230khz and 340khz. the demodulator demodulates the i and q channel outputs and produces a digital data output. it detects the relative phase of the i and the q channel signal. if the i channel signal lags the q channel, the fsk tone frequency lies above the lo frequency (data ?1?). if the i channel leads the q channel, the fsk tone lies below the lo frequency (data ?0?). the output of the receiver is available on the dataixo pin. a rssi circuit (receive signal strength indicator) indicates the received signal level. front end a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000011 lna_by pa2 pa1 pa0 sync_en mode1 mode0 load_en a low noise amplifier in rf receivers is used to boost the incoming signal prior to the frequency conversion process. this is important in order to prevent mixer noise from domi- nating the overall front-end noise performance. the lna is a two-stage amplifier and has a nominal gain of approximately 23db at 900mhz. the front end has a gain of about 33db to 35db. the gain varies by 1-1.5db over a 2.0v to 2.5v variation in power supply. the lna can be bypassed by setting bit lna_by to ?1?. this can be useful for very strong input signal levels. the front-end gain with the lna bypassed is about 9-10db. the mixers have a gain of about 10db at 900mhz. the differential outputs of the mixers can be made available at pins ichout and qchout. the output impedance of each mixer is about 8k w . the input impedance is close to 50k w as shown in figure 8, giving an input reflection of about -20db. the receiver does not require any matching network. figure 11. lna input impedance
micrf505 micrel m9999-051304 18 may 13, 2004 sallen-key filters a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000001 modulation1 modulation0 "0" "0" rssi_en ld_en pf_fc1 pf_fc0 each channel includes a pre-amplifier and a prefilter, which is a three-pole sallen-key lowpass filter. it protects the following switched-capacitor filter from strong adjacent chan- nel signals, and it also works as an anti-aliasing filter. the preamplifier has a gain of 22-23db. the maximum output voltage swing is about 1.4vpp for a 2.25v power supply. in addition, the if amplifier also performs offset cancellation. gain varies by less than 0.5db over a 2.0 - 2.5v variation in power supply. the third order sallen-key low pass filter is programmable to four different cut-off frequencies according to the table below: switched capacitor filter a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000000 ?1? scclk_x2 scclk5 scclk4 scclk3 scclk2 scclk1 scclk0 pf_fc1 pf_fc0 cut-off freq. (khz) 0 0 100 0 1 150 1 0 230 1 1 340 the main channel filter is a switched-capacitor implementa- tion of a six-pole elliptic low pass filter. the elliptic filter minimizes the total capacitance required for a given selectiv- ity and dynamic range. the cut-off frequency of the switched- capacitor filter is adjustable by changing the clock frequency. the clock frequency is designed to be 20 times the cut-off frequency. the clock frequency is derived from the reference crystal oscillator. a programmable 6-bit divider divides the frequency of the crystal oscillator. to generate the correct non-overlapping clock-phases needed by the filter this fre- quency is then divided by 4. the cut-off frequency of the filter is given by: f f 80 scclk cut xco = ? when scclk_x2=0 and f f 40 scclk cut xco = ? when scclk_x2=1 where: f cut : filter cutoff frequency f xco : crystal oscillator frequency scclk: switched capacitor filter clock, bits scclk5-0 for instance, for a crystal frequency of 32mhz and if the 6 bit divider divides the input frequency by 5 the cut-off frequency of the sc filter is 32mhz/(80 5) = 80khz 1st order rc low pass filters are connected to the output of the sc filter to filter the clock frequency. the lowest cutoff frequency in the pre- and the main channel filter must be set so that the received signal is passed with no attenuation, that is frequency deviation plus modulation. if there are any frequency offset between the transmitter and the receiver, this must also be taken into consideration. a formula for the receiver bandwidth can be summarized as follows; f f f baudrate / 2 bw offset dev =+ + + where f bw : needed receiver bandwidth, fcut above should not be smaller than f bw (hz) f offset : total frequency offset between receiver and transmitter [hz] f dev : single-sided frequency deviation, see chapter modulator on how to calculate (hz) baudrate: the baud rate given in bit/sec
may 13, 2004 19 m9999-051304 micrf505 micrel rssi a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000001 modulation1 modulation0 "0" "0" rssi_en ld_en pf_fc1 pf_fc0 0 0,5 1 1,5 2 2,5 -110 -100 -90 -80 -70 -60 -50 -40 pin p i n (dbm) ( d b m ) rssi figure 12. rssi voltage c10 1nf r2 33k pin 14 rssi rssi figure 13. rssi network a typical plot of the rssi voltage as function of input power is shown in figure 9. the rssi has a dynamic range of about 50db from about -110dbm to -60dbm input power. the rssi can be used as a signal presence indicator. when a rf signal is received, the rssi output increases. this could be used to wake up circuitry that is normally in a sleep mode configuration to conserve battery life. another application for which the rssi could be used is to determine if transmit power can be reduced in a system. if the rssi detects a strong signal, it could tell the transmitter to reduce the transmit power to reduce current consumption.
micrf505 micrel m9999-051304 20 may 13, 2004 fee a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000001 ? ? ? ? feec_3 feec_2 feec_1 feec_0 0000001 fee_7 fee_6 fee_5 fee_4 fee_3 fee_2 fee_1 fee_0 the frequency error estimator (fee) uses information from the demodulator to calculate the frequency offset between its receive frequency and the transmitter frequency. the output of the fee can be used to tune the xco frequency, both for production calibration and for compensation for crystal tem- perature drift and aging. the input to the fee circuit are the up and down pulses from the demodulator. every time a ?1? is updated, an up-pulse is coming out of the demodulator, and the same with the dn- pulse every time the ?0? is updated. the expected no. of pulses for every received symbol are 2 times the(modulation index ( d ). the fee can operate in three different modes; counting only up-pulses, only dn-pulses or counting up+dn pulses. the no. of received symbols to be counted are either 8, 16, 32 or 64. this is set by the feec_0..feec_3 control bit, as follows: feec_1 feec_0 fee mode 0 0 off 0 1 counting up pulses 1 0 counting dn pulses 1 1 counting up and dn pulses. up increments the counter, dn decrements it. feec_3 feec_2 no. of symbols used for the measurement 008 0116 1032 1164 table 10. feec control bit the result of the measurement is the fee value, this can be read from register with address 0010110b. negative values are stored as a binary no between 00000000 and 11111111. to calculate the negative value, a two?s complement of this value must be performed. only fee modes where dn-pulses are counted (10 and 11) will give a negative value. when the fee value has been read, the frequency offset can be calculated as follows: mode up: foffset = r/(2p) (fee - d fp mode dn: foffset = r/(2p) (fee + d fp mode up+dn: foffset = r/(4p) (fee where fee is the value stored in the fee register, (fp is the single sided frequency deviation, p is the no. of symbols/data bit counted and r is the symbol/data rate. a positive foffset means that the received signal has a higher frequency than the receiver frequency. to compensate for this, the receivers xco frequency should be increased ( see annex a ) on how to tune the xco frequency based on the fee value). it is recommended to use mode up+dn for two reasons, you do not need to know the actual frequency deviation and this mode gives the best accuracy.
may 13, 2004 21 m9999-051304 micrf505 micrel bit synchronizer a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000110 ? modclks2 modclks1 modclks0 bitsync_clks2 bitsync_clks1 bitsync_clks0 bitrate_clks2 0000111 bitrate_clks1 bitrate_clks0 refclk_k5 refclk_k4 refclk_k3 refclk_k2 refclk_k1 refclk_k0 a bit synchronizer can be enabled in receive mode by selecting the synchronous mode (sync_en=1). the dataclk- pin will output a clock with twice the frequency of the bit rate (a bit rate of 20 kbit/sec gives a dataclk of 20 khz). a received symbol/bit on dataixo will be output on rising edge of dataclk. the micro controller should therefore sample the symbol/bit on falling edge of dataclk. the bit synchronizer uses a clock which needs to be pro- grammed according to the bit rate. the clock frequency should be 16 times the actual bit rate (a bit rate of 20 kbit/sec needs a bit synchronizer clock with frequency of 320 khz). the clock frequency is set by the following formula: f f refclk_k 2 bitsync_clk xco = - () 7 bitsync clks _ where f bitsync_clk : the bit synchronizer clock fre- quency (16 times higher than the bit rate) f xco : crystal oscillator frequency refclk_k: 6 bit divider, values between 1 and 63 bitsync_clks: bit synchronizer setting, values between 0 and 7 refclk_k is also used to derive the modulator clock and the bit rate clock. at the beginning of a received data package, the bit synchro- nizer clock frequency is not synchronized to the bit rate. when these two are maximum offset to each other, it takes 22 bit/symbols before synchronization is achieved. transmitter power amplifier a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000000 lna_by pa2 pa1 pa0 sync_en mode1 mode0 load_en 0000001 modulation1 modulation0 "0" "0" rssi_en ld_en pf_fc1 pf_fc0 the maximum output power is approximately 10dbm for a 50 w load. for maximum output power the load seen by the pa must be resistive. higher output power can be obtained by decreasing the load impedance. however, this will be in conflict with obtaining impedance match in the lna. the output power is programmable in seven steps, with approxi- mately 3db between each step. this is controlled by bits pa2 - pa0. pa2 - pa0 = 1 give the maximum output power. the power amplifier can be turned off in by settingpa2 - pa0 = 0. for all other combinations the pa is on and has a maximum power when pa2 - pa0 = 1. the pa has 7 power levels in this case. the output power vary about 3db over power supply 2.0v to 2.5v and about 2db over temperature ?40oc to +85oc. the 2nd and 3rd harmonic of the pa are as follows: 2nd harmonic: <-25dbm 3rd harmonic: <-15dbm to reduce the emission of harmonics, a lc filter can be added between the ant pin and the antenna as shown in figure 11. c8 10pf c7 10pf l1 4.7nh pin 5 ant figure 14. lc filter this filter is designed for the 915mhz band with 50ohm terminations. the component values may have to be tuned to compensate for layout parasitics. this filter may also in- crease the receiver selectivity.
micrf505 micrel m9999-051304 22 may 13, 2004 frequency modulation a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000001 modulation1 modulation0 ?0? pa_ldc_en rssi_en ld_en pf_fc1 pf_fc0 modulation1 modulation0 modulation type 0 0 closed loop modulation using modulator 0 1 not in use 1 0 fsk applied using two sets of dividers 1 1 not in use table 11. modulation bit setting when modulation1 and modulation0 is 00, the modulator needs to be programmed properly, see ?modulator? section. the modulation signal will now be applied directly on the phase locked vco. it is therefore important that the pll bandwidth is not too high, as this will remove the modulation. see ?pll filter? section on how to calculate the pll compo- nents. when using the modulator the modulation signal is applied to the vco and therefore some sort of encoding is needed. the level of encoding is determined by the pll loop filter bandwidth and data rate. two of the most common encoding techniques are manchester encoding and 3b4b. other en- coding schemes may also be used. manchester encoding is when one bit is encoded in to a two- bit word and is shown in table 10. when using manchester encoding the maximum overhead is 100%. when selecting pll loop filter it is important to note that the min baud rate is equal to: f baud / s 4 baud_min = f baud_min : the minimum frequency of the baud rate (hz) baud/s: elements per second (encoded data) data word ?0? ?10? ?1? ?01? table 12. manchester encoding another much more efficient encoding type is 3b4b where three data bits are encoded into a four-bit word. the reason for encoding is to minimize the dc component in the modu- lated data. to have minimum dc component each four bit word should include two elements of ?1? and two elements of ?0?. following this guidance only 6 out of 8 word complies and two encoded words needs special precaution. whenever 000 and 111 data appear, the user must set/clear a flag that indicate if last encoded word was ?word a? and select the respective encoded word shown in table 11. data word a word b 000 1011 0100 001 1100 010 0011 011 1010 100 0101 101 1001 110 0110 111 1101 0010 table 13. 3b4b enconding data bits encoded words comments 000 000 000 000 000 1011 0100 1011 0100 1011 a flag indicates if ?word a? has been used 111 111 010 110 000 1101 0010 0011 0110 1011 a flag indicates if ?word a? has been used table 14. example of 3b4b encoding
may 13, 2004 23 m9999-051304 micrf505 micrel when modulation1 modulation0 is 10, two sets of divider values need to be programmed. the formula for calculating the m,n and a values is given in chapter frequency synthe- sizer. the divider values stored in the m0-, n0- and a0- registers will be used when transmitting a ?0? and the m1-, n1- and a1-registers will be used to transmit a ?1?. the difference between the two carrier frequencies corresponds to the double sided frequency modulation. opposite from the modu- lation with the modulator, the pll shall now lock on a new frequency for every change in the transmitted data. the pll bandwidth therefore needs to be relatively high, higher bit rate requires a higher pll bandwidth and vice versa. the data to be transmitted shall be applied to pin dataixo (see chapter transceiver sync-/non-synchronous mode on how to use the pin dataclk). the dataixo pin is set as input in transmit mode and output in receive mode. when set as input, a weak voltage divider will set the level to vdd/2, when it is not pulled up or down by the controller. when using the modulator, it is important that the dataixo is kept tristated until the transmission shall begin (when pll is in lock and the pa is turned on). when dataixo is tristated, the pll will lock on the lo frequency (used in receive mode). when dataixo is set either high or low, the rf frequency will be shifted up or down, centered around the lo-frequency. this is only important when using the modulator, for the other modulation method, if dataixo is tristated, the m0-, n0 and a0 registers will be used. modulator a6..a0 d7 d6 d5 d4 d3 d2 d1 d0 0000100 mod_f2 mod_f1 mod_f0 mod_i4 mod_i3 mod_i2 mod_i1 mod_i0 0000101 ? ? ?0? ?1? mod_a3 mod_a2 mod_a1 mod_a0 0000110 ? mod_clks2 mod_clks1 mod_clks0 bitsync_clks2 bitsync_clks1 bitsync_clks0 bitrate_clks2 0000111 bitrate_clks1 bitrate_clks0 refclk_k5 refclk_k4 refclk_k3 refclk_k2 refclk_k1 refclk_k0 the modulator will create a waveform with programmable amplitude and frequency. this waveform is fed into a modu- lation varactor in the vco which will create the desired frequency modulation. the frequency spectrum can be nar- rowed by increasing the rise- and fall times of the waveform. the modulator waveform is created by charging and dis- charging a capacitor. a modulator clock controls the timing, as shown in figure 13. for every rise- and fall edge, 4 clock periods are being used. the charging current during these 4 clock periods are not equal, this is to reduce the high- frequency components in the waveform, which in turn will narrow the frequency spectrum. the frequency deviation can be set in three different ways, as will be explained below. a formula for setting the desired deviation is given at the end of this chapter. modulator clock modulator waveform figure 15. modulator waveform and clock modulator clock the modulator clock frequency is set by: f f refclk_k 2 mod_clk xco 7 mod_clks = () where f mod_clk is the modulator clock shown in figure 13, f xco is the crystal oscillator frequency, refclk_k is a 6 bit number and mod_clks is a 3 bit number. mod_clks can be set to a value between 0 and 7. the modulator clock frequency should be set according to the bit rate and shaping. mod_clka mod_clkb mod_clkb > mod_clka figure 16. two different modulator clock settings a f mod_clk of 8 times the bit rate (as in figure 14) corre- sponds to a signal filtered in a gaussian filter with a bandwidth(period-product (bt) of 1. when bt is increased, the waveform will be less filtered. minimum bt is 1 (mod_clk is 8 times the bitrate). figure 14 shows two waveforms with bt=1 and bt=2, i.e. the mod_clk is 8 and 16 times higher than the bit rate. when changing the bt factor, the charge- and discharge times will also be changed, and therefore the frequency deviation, as shown in figure 15.
micrf505 micrel m9999-051304 24 may 13, 2004 modulator current the current used during the rise- and fall times can be programmed with the mod_i4..mod_i0 bit, the last one being lsb. figure 15 shows two waveforms generated with two different currents, where mod_ia > mod_ib. higher current will give a higher frequency deviation and vice versa. the effect of modulator clock and mod_1 is illustrated by to avoid saturation in the modulator it it important not to exceed maximum mod_i. max mod_i for a given fmod_clk is given by: where min() returns the value of the smallest argument and int() returns the integer part of the argument. where int(x): integer and and f_mod_clk: modulater clk frequency. mod_la mod_lb mod_la > mod_lb figure 17. two different modulator current settings modulator attenuator a third way to set the deviation is by programming the modulator attenuator, mod_a2..mod_a0, the last being lsb. the purposes of the attenuator is to allow small deviations when the bit rate is small and/or the bt is small (these settings will give a relatively slow modulator clock, and therefore long rise- and fall times, which in turn results in large frequency deviations). in addition, the attenuator will improve the reso- lution in the modulator. mod_aa mod_ab mod_ab > mod_ab figure 18. two different modulator attenuator settings the attenuation is given by: where v mod2 and v mod1 is the modulator amplitude after and before the attenuator, respectively. figure 16 shows two waveforms with different attenuator setting; mod_aa < mod_ab. if mod_a is increased, the frequency deviation is lowered and vice versa. modulator filter to reduce the high-frequency components in the generated waveform, a filter with programmable cut-off frequency can be enabled. this is done using mod_f2..mod_f0, the last one being lsb. the mod_f should be set according to the formula: mod_f bitrate = 150 10 3 mod_filter on mod_filter off figure 19. modulator waveform with and without filtering mod_f=0 disables the modulator filter and mod_f=7 gives most filtering. figure 18 shows a waveform with and without the filter. calculation of the frequency deviation the parameters influencing the frequency deviation can be summarized in the following equations: f f refclk_k 2 mod_clk xco = () 7 mod clks _ where : f dev : single sided frequency deviation [hz] f xco : crystal oscillator frequency [hz] f rf : center frequency [hz] refclk_k: 6 bit divider, values between 1 and 63 mod_clks: modulator clock setting, values between 0 and 7 f mod_clk : modulator clock frequency, derived from the crystal frequency, refclk_k and mod_clks mod_i: modulator current setting, values between 0 and 31 mod_a: modulator attenuator setting, values between 0 and 15 f mod_1 f deviation mod_clk a mod_imax int(f_mod_clk 28e - 6) -1 = ? v 1 1 mod_a mod2 a + f mod_i f 1 mod_a f dev mod_clk rf = ? + ? - ?? () 1 44 28 10 72 9 .
may 13, 2004 25 m9999-051304 micrf505 micrel the modulator filter will not influence on the frequency deviation as long as the programmed cut-off frequency is above the actual bit rate. the frequency deviation must be programmed so that the modulation index (2 x single sided frequency deviation/ baudrate [bps]) always is greater than or equal to 2 including the total frequency offset between the receiver and the transmitter: f baudrate f dev offset =+ the calculated f dev should be used to calculate the needed receiver bandwidth, see chapter switched capacitor filter. using the xco-tune bits the rf chip has a built-in mechanism for tuning the fre- quency of the crystal oscillator and is often used in combina- tion with the frequency error estimator (fee). the xco tuning is designed to eliminate or reduce initial frequency tolerance of the crystal and/or the frequency stability over temperature. figure 20: crystal oscillator?s external components if the value in xco_tune is increased (adding capacitance), the frequency will decrease. the xco uses two external capacitors. the value of these will strongly affect the tuning range. with a 16.0 mhz crystal (tn4-26011 from toyocom), and external capacitor values of 1.5 pf, the tuning range will be (almost) equally divided between increase frequency and decrease frequency. that is, xco_tune values greater than approx 16 will de- crease frequency, and xco_tune values less than approx 16 will increase frequency. figure. 21 xco tuning a procedure for using the xcotuning feature in combination with the fee is given below. the micrf505 measures the frequency offset between the demodulated signal and the lo and tune the xco so the lo frequency is equal to received carrier frequency. a procedure like this can be called during production (storing the calibrated xco_tune value), at regular intervals or imple- mented in the communication protocol when the frequency has changed. the fee can count ?up?-pulses and/or ?down?-pulses (pulses out of the demodulator when a logic ?1? or logic ?0?, resp., is received). the fee can count pulses for n bits, where n = 8, 16, 32 or 64. example: in fee, count up+dwn pulses, counting 8 bits: a perfect case ==> fee = 0 if fee > 0: lo is too low, increase lo by decreasing xco_tune value v.v. for fee <0 fee field holds a a number in the range -128 , ... , 127 however, it keeps counting above/below the range, that is: if fee=-128 and still counting dwn-pulses: 1) => -129 = +127 2) 126 3) 125 ... to avoid this situation, always make sure max count is between limits. suggestion: count for 8 (or 16) bits only. procedure description in the procedure below, up+dwn pulses are counted, and only the sign of the fee is used. the value of n is 8 or 16. assumption: a transmitter is sending a 1010... pattern at the correct frequency and bitrate the wanted receiver frequency is the mid-point between the ?0? and ?1? frequencies input: nothing output: the best xco_tune value (giving the lowest |fee|) local variables: -60,0 -40,0 -20,0 0,0 20,0 40,0 60,0 80,0 100,0 0 8 16 24 32 xco bitvalue 2x1.5pf 2x0pf pin 24, xtalout xtalin, pin 23 c10 1.5pf c11 1.5pf y1 tsx-10a
micrf505 micrel m9999-051304 26 may 13, 2004 xco_present (5-bit) holds present value in xco_tune bits xco_step (4-bit) holds increment/decrement of xco_tune bits xco_sign (1 bit) holds pos or neg (increment/decrement) increasing lo is done by reducing the xco_tune value xco tune procedure init: xco_present = 0 xco_step = 32 xco_sign = neg control_word = default rx, clocks match transmitter loop: xco_step = xco_step/2 xco_sign == pos? yes > xco_present -= xco_step // increase lo no > xco_present += xco_step // decrease lo xco_tune bits = xco_present program rfchip delay > n bits read fee fee > 0? yes > xco_sign = pos no > xco_sign = neg // negative or == 0 xco_step > 1? yes > branch to loop no > xco_sign == pos? yes > xco_present -= 1 branch to fin fin: return, return-value = xco_present
may 13, 2004 27 m9999-051304 micrf505 micrel micrel, inc. 1849 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 web http://www.micrel.com the information furnished by micrel in this data sheet is believed to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and specifications at any time without notification to the customer. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intend ed for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant inj ury to the user. a purchaser?s use or sale of micrel products for use in life support appliances, devices or systems is at purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2004 micrel, incorporated.

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