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cml semiconductor products tone detector fx105a ? 1996 consumer microcircuits limited d/105a/3 december 1995 1.0 features advance information operates in high noise conditions adjustable bandwidth 3 3 36db signal input range adjustable frequency high sensitivity wide voltage range (2.7v to 5.5v) low power single and multitone system applications
tone detector fx105a ? 1996 consumer microcircuits limited 2 d/105a/3 contents section page 1.0 features ................................ ................................ ................................ .......... 1 1.1 brief description ................................ ................................ ............................ 1 1.2 block diagram ................................ ................................ ................................ 3 1.3 signal list ................................ ................................ ................................ ....... 4 1.4 external components ................................ ................................ .................... 5 1.5 general description ................................ ................................ ....................... 6 1.6 application notes ................................ ................................ .......................... 7 1.6.1 general ................................ ................................ ............................ 7 1.6.2 method for calculating external component values ....................... 7 1.7 performance specification ................................ ................................ ......... 12 1.7.1 electrical performance ................................ ................................ .. 12 1.7.2 packaging ................................ ................................ ...................... 14
tone detector fx105a ? 1996 consumer microcircuits limited 3 d/105a/3 1.2 block diagram
tone detector fx105a ? 1996 consumer microcircuits limited 4 d/105a/3 1.3 signal list package d4/p3 signal description pin no. name type 1 input amp in i/p ac couple to this input of the input buffer amplifier. 2 input amp out o/p the input buffer amplifier output. 3 rw i/p the input to the detect/word filter. 4 rv i/p the input to the vco loop filter. 5 c3a o/p word filter capacitor pin a. 6 c3b o/p word filter capacitor pin b. 7 c2a o/p vco loop filter capacitor pin a. 8 c2b o/p vco loop filter capacitor pin b. 9 detect out o/p open drain pmos output, active on detect. note that a load resistor to v ss is required. 10 v ss power ground. 11 r2hi i/p bandwidth control resistor pin a. 12 r2lo i/p bandwidth control resistor pin b. 13 c1b o/p vco capacitor b. 14 c1a o/p vco capacitor a. 15 r1 i/p vco discharge resistor. when potentiometer tuning is required, a series resistor is recommended to prevent possible shorting to ground. 16 v dd power power supply. notes: i/p = input o/p = output
tone detector fx105a ? 1996 consumer microcircuits limited 5 d/105a/3 1.4 external components
tone detector fx105a ? 1996 consumer microcircuits limited 6 d/105a/3 1.5 general description the input signal t o the fx105a is ac coupled to the buffer amplifier input, which is internally biased at 50% of supply voltage. the signal appears at the output of the buffer amplifier as an ac voltage superimposed on the dc bias level. the signal is then coupled via r v and r w to the voltage controlled oscillator (vco) and word sampling switches, which cyclically connect c 2 and c 3 into the circuit to form four sample-and-hold rc circuit integrators. see figure 3. with no input signal level, each capacitor charges to t he dc bias level so differential voltages are zero. when an input signal is applied each capacitor receives an additional charge. this charge is determined by the integrated average of the signal waveform during the time the capacitor is switched into the circuit. figure 3 shows the operating sequence of the vco sampling switches and their relationship to a locked-on in-band signal. c 2a and c 2b should not receive any additional charge since they always sample the input as it crosses the dc bias level. should the signal not be locked to the vco, a positive or negative charge voltage will appear on c 2a or c 2b . this voltage, when differentially amplified, is applied to the vco as an error correcting signal to enable the vco to ? lock. ? figure 3 also shows the operating sequence of the ? word ? sampling switches and their relationship to a locked-on in-band signal. as the figure shows, the charge applied to c 3a should always be positive, and the charge applied to c 3b should always be negative (with respect to the common bias level). these capacitor potentials are differentially amplified and applied to a dc comparator, which switches at a pre-determined threshold voltage v th . the comparator output is a logic signal used to control a counter. this counter switches the fx105a output on when the comparator output is maintained in the ? word present ? state for a minimum number of consecutive signal samples. the activated output switch reduces the comparator threshold by 50%, introducing threshold hysteresis. output chatter with marginal input signal amplitudes is thereby minimised.
tone detector fx105a ? 1996 consumer microcircuits limited 7 d/105a/3 1.6 application notes 1.6.1 general the external components shown in figure 2 are used to adjust the various performance parameters of the fx105a. the signal-to-noise performance, response time and signal bandwidth are all interrelated factors which should be optimised to meet the requirements of the application. by selecting component values in accordance with the following formulae, optimum circuit performance is obtained for any given application. first define the following application parameters: (a) the input frequency to be detected (f 0 ). the free running frequency of the vco is set to 6 times this frequency by observing the output across c 1 or r 1 . (the frequency observed at pin 15 (r 1 ) is 6 x f 0 and the frequency observed at pins 13 or 14 (c 1a or c 1b ) is 3 x f 0 ). (b) the fx105a minimum usable bandwidth (mubw). this is obtained by taking into account the worst case tolerances ( d f 0 ) of the input frequency and the variations in the fx105a vco frequency due to supply voltage ( d v dd ) and temperature ( d temp) variation of the fx105a and its supporting components. (c) the maximum permissible fx105a response time. (d) the minimum input signal amplitude. (e) the maximum input signal amplitude. using this information the appropriate component values can be calculated, and the signal-to-noise performance can be read from a chart. do not add large safety margins for response time and minimum signal amplitude: reasonable margins are already included in the formulae. excessive margins may result in reduced noise immunity. 1.6.2 method for calculating external component values the example on the following pages demonstrates the calculation of component values for any given application. for the purpose of this example, the values below are used: (a) f 0 = 2800 hz (b) d temp = 100c, d v dd = 1v, d f 0 = 0.5% (c) maximum allowed response time t on = 50msec (d) minimum input signal amplitude v in min = 200 mvrms (e) maximum input signal amplitude v in max = 400 mvrms 1.6.2.1 calculate r 1 c 1 (c 1a = c 1b ) the components r 1 , c 1a and c 1b set the free running frequency of the vco and therefore the f 0 of the fx105a. as shown below, the frequency of 2800 hz corresponds to a capacitor value of 220 pf and a resistor value of 385k w . this resistance can be achieved with a 300 k w fixed resistor and a 100k w potentiometer. r 1 should lie in the range 100k w to 680k w . r 1 c 1a = 1/ [2kf 0 ] = 1/ (2 x 2.1 x 2800) = 85sec where k is a constant = 2.1 5%. note that above f 0 = 1khz, the value of k increases with f 0 up to a maximum of 2.5 at 20khz. therefore r 1 ? 385k w for c 1a = c 1b = 220pf
tone detector fx105a ? 1996 consumer microcircuits limited 8 d/105a/3 1.6.2.2 calculate minimum usable bandwidth (%) minimum usable bandwidth (mubw) is the total (%) bandwidth required for the following: (a) input signal frequency tolerance ( d f 0 ) (b) fx105a vco temperature coefficient (t c = - 100 ppm/ oc) (c) fx105a vco supply volta ge coefficient (v c = 2330 ppm/v) add (a), (b) and (c) and express as total (%) bandwidth, not as a (%) value. mubw = d f 0 + |t c | d temp + v c d v dd mubw = 0.5 + 0.01 x 100 + 0.233 x 1 ? 2% 1.6.2.3 calculate the recommended operating bandwidth note again that this is the total (%) bandwidth: bw = ? [10 + mubw] = ? (10 + 2) = 6% 1.6.2.4 select r 2 for operating bw r 2 = 4.8 bw/ [10.35 - bw] = 4.8 x 6/ (10.35 - 6) ? 6.8k w the exact bandwidth given by any value of r 2 will vary slightly. in applications where an exact bandwidth is required, r 2 should be a variable resistor to permit adjustment. 1.6.2.5 calculate r v c 2a (c 2a = c 2b ) use nearest preferred values r v c 2a ? 100/ [3 f 0 bw] ? 100/ (3 x 2800 x 6) ? 2msec therefore r v ? 200k w for c 2a = c 2b = 10nf 1.6.2.6 define the maximum allowed response time the maximum response time (t on ) is the sum of the vco lock time (t lock ) and the word integration time (t word ). the fx105a?s t on must not exceed the maximum time allowed for the application, but a value lying near the maximum gives the best s/n performance. (a) calculate t lock t lock = 150/ [f 0 bw] = 150/ (2800 x 6) ? 9msec note: t lock may vary from near zero to the value given, causing corresponding variations in actual t on . (b) calculate maximum allowable t word t word = t on max - t lock = 50 - 9 = 41 msec note: since the maximum allowed response time (t on ) is 50 msec, a maximum word integration time of 41 msec is available.
tone detector fx105a ? 1996 consumer microcircuits limited 9 d/105a/3 1.6.2.7 calculate r w c 3a (c 3a = c 3b ) use nearest preferred values. r w c 3a ? t word / [ - 3in (1 - v th / v in min ) ] where v th is the word filter sensitivity, see section 1.7.1 a signal amplitude of 200 mv and a resistor value r w of 510k w with a 0.1f capacitor for c 3a and c 3b will yield a t word time of 20msec. this in turn yields a response time of 9msec + 20msec = 29msec. 1.6.2.8 calculate the maximum de-response time t off ? - 3 r w c 3a in (v th / v in max ) where v th is the word filter sens itivity, see section 1.7.1 for improved de-response time, a diode (1n914 or similar) can be placed between pins 5 and 6, as shown in figure 2. the formula and figure below show the approximate time the fx105a will take to turn off after an in-band signal has been removed. the effect of this diode is to greatly reduce the turn- off time with signal input amplitudes greater than 300 mv rms . figure 4 is for v dd = 5v; for lower v dd then k dt increases. t off ? k dt r w c 3a so for a maximum signal amplitude of 400mv, a resistor value r w of 510k w with a 0.1f capacitor for c 3a and c 3b and a diode between pins 5 and 6, a de-response time of ? 182 msec is obtained.
tone detector fx105a ? 1996 consumer microcircuits limited 10 d/105a/3 1.6.2.9 calculate signal to noise performance worst-case s/n calculations depend on calculation of a value ? m ? using the formula shown below: m = r w c 3a / [3 r v c 2a ] substituting our example values, m = 510 x 0.1 / (3 x 200 x 0.01) = 8.5 by substituting this value for m in figure 5 the minimum required s/n of an in band tone with respect to an adjacent interfering tone can be found. this has to be increased if the required tone amplitude is close to the word filter sensitivity v th .
tone detector fx105a ? 1996 consumer microcircuits limited 11 d/105a/3 1.7 performance specification 1.7.1 electrical performance absolute maximum ratings exceeding these maximum ratings can result in damage to the device. min. max. units supply (v dd - v ss ) -0.3 7.0 v voltage on any pin to v ss -0.3 v dd + 0.3 v current into or out of v dd and v ss pins -30 +30 ma current into or out of any other pin -20 +20 ma maximum output switch load current +10 ma p3/d4 package min. max. units total allowable power dissipation at tamb = 25c 800 mw ... derating 13 mw/c storage temperature -55 +125 c operating temperature -30 +85 c operating limits correct operation of the device outside these limits is not implied. notes min. max. units supply (v dd - v ss ) 2.7 5.5 v operating temperature -30 +85 c
tone detector fx105a ? 1996 consumer microcircuits limited 12 d/105a/3 operating characteristics for the following conditions unless otherwise specified: v dd = 3.0v to 5.0v, tamb = - 40c to +85c, load resistance on decoder output pin = 20k w notes min. typ. max. units static parameters i dd 2 0.9 3.0 ma amplifier input impedance 200 k w digital output impedance 500 w analogue output impedance 1000 w dynamic parameters input signal amplitude 2 1.0 vrms frequency 40 20,000 hz response threshold 1 18 38 mvrms deresponse threshold 1 5 9 mvrms bw range 5 10 %f 0 signal to noise performance -6 -9 db (f 0 /2) subharmonic rejection 30 db (5 f 0 ) harmonic rejection 20 db vco frequency 3 240 120,000 hz frequency stability ( d temp) 3 100 ppm/c frequency stability ( d v dd ) 3 2330 ppm/v amplifier open loop gain 60 db gain bandwidth product 1.0 mhz closed loop gain 0 db word commutating filter sensitivity (v th ) 4 12.5 mvrms notes: 1. with diode (d 1 ) fitted. 2. for v dd = 5v. multiply by v dd /5v for other supply values. 3. observing pins 13, 14 or 15 (d4/p3 package ) will cause a frequency shift due to additional loading. if tuning the centre frequency by observing the vco, design in a buffer amplifier between pin 15 and the probe/calibration point and tune with no input signal. otherwise, tune by observing the detect output band edges while sweeping the input signal. 4. adjust according to equation for r 2 in section 1.6.2.
tone detector fx105a ? 1996 consumer microcircuits limited 13 d/105a/3 1.7.2 packaging
tone detector fx105a handling precautions: this product includes input protection, however, precautions should be taken to prevent device damage from electro-static discharge. cml does not assume any responsibility for the use of any circuitry described. no ipr or circuit patent licences are implied. cml reserves the right at any time without notice to change the said circuitry and this product specification. cml has a policy of testing every product shipped using calibrated test equipment to ensure compliance with this product specification. specific testing of all circuit parameters is not necessarily performed. consumer microcircuits limited 1 wheaton road telephone: +44 1376 513833 witham - essex cm8 3td - england telefax: +44 1376 518247

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