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SL1461SA
Wideband PLL FM Demodulator Advance Information
The SL1461SA is a wideband PLL FM demodulator, intended primarily for application in satellite tuners. The device contains all elements necessary, with the exception of external oscillator sustaining network and loop feedback components, to form a complete PLL system operating at frequencies up to 800MHz. An AFC with window adjust is provided, whose output signal can be used to correct for any frequency drift at the head end local oscillator.
DS4358 ISSUE 1.3 September 1999
Ordering Information
SL1461SA/KG/MPAS
FEATURES I Single chip PLL system for wideband FM demodulation I Simple low component count application I Allows for application of threshold extension I Fully balanced low radiation design I High operating input sensivity I Improved VCO stability with variations in supply or temperature I AGC detect and bias adjust I 75 video output drive with low distortion levels I Dynamic self biasing analog AFC I Full ESD Protection*
* Normal ESD handling procedures should be observed
AFC PUMP AFC WINDOW ADJUST VEE OSCILLATOR + OSCILLATOR - AGC BIAS AGC OUTPUT RF INPUT
1 2 3 4 5 6 7 8
16 15
AFC OUTPUT VCC VIDEO FEEDBACK + VIDEO - VIDEO + VIDEO FEEDBACK - VIDEO OUTPUT RF INPUT
SL1461SA
14 13 12 11 10 9
MP16
Fig.1 Pin connections - top view
APPLICATIONS I Satellite receiver systems I Data communications Systems
AGC BIAS RF INPUTS AGC OUTPUT
6 8 9 7
14 12 13 11
VIDEO FEEDBACK + VIDEO + VIDEO - VIDEO FEEDBACK - VIDEO OUTPUT AFC PUMP AFC OUTPUT
10
1
LOCAL OSCILLATOR AFC WINDOW ADJUST
4 5
16
2
Fig.2 SL1461SA block diagram
SP1461SA
Advance Information
ELECTRICAL CHARACTERISTICS
Tamb = -20C to +80C, VCC = +4.5V to +5.5V. The electrical characteristics are guaranteed by either production test or design. They apply within the specified ambient temperature and supply voltage unless otherwise stated. Characteristics Min. Supply current Operating frequency Input sensitivity Input overload VCO sensitivity (dF/dV) VCO linearity VCO supply stability VCO temperature stability Phase detector gain Loop amplifier input impedance Loop amplifier output impedance Loop amplifier open loop gain Loop amplifier gain bandwidth product Loop amplifier output swing Video drive output impedance Video drive: Luminance nonlinearity - differential gain - differential phase - intermodulation - signal/noise - Tilt - baseline distortion AGC output current AGC bias current AFC window current AFC charge pump current AFC leakage current AFC output saturation voltage 10 0 0 50 10 0.4 66 72 0.3 0.4 3 2 400 250 400 1.9 0.5 1.0 5 2.5 3 -40 % % Degree dB dB % % A A A A A V With charge pump disabled AFC output enabled 400A gives 1.5V deadband window 1K load, See note 3 and 4 75K load, See note 3 and 4 75K load, See note 3 and 4 See notes 1, 3 and 4 1K load, See note 2 and 4 1K load, See note 3 and 4 1K load, See note 3 and 4 Maximum load voltage drop 2V 55 75 450 0 25 32 25 2.0 20 0.5 0.25 570 25 38 240 1.2 95 700 39 300 -40 Value Typ. 36 Max. 40 800 mA MHz dBm dBm MHz/V % MHz/V KHz/C V/rad V/rad dB MHz Vp-p Refer to application in Fig. 3 Refer to application in Fig. 3; with 13.5MHz p-p deviation See note 5 See note 5 Differential loop filter Single ended loop filter Single ended Single ended Single ended Single ended Single ended Preamp limiting Units Conditions
Note 1. Product of input modulation f 1 at 4.43MHz, 13.5MHz p-p deviation and f 2 at 6MHz p-p deviation, (PAL chroma and sound subcarriers). Note 2. Ratio of output video signal with input modulation at 1MHz, 13.5MHz p-p deviation, to output rms noise in 6MHz bandwidth with no input modulation. Note 3. Input test signal pre-emphasised video 13.5MHz p-p deviation. Output voltage 600mV pk-pk. Note 4. See page 3 Note 5. Assuming operating frequency of 479.5MHz set with VCC @ 5.0V and ambient temperature of +20C. Only applies to Application shown in Fig. 3. also refer to Fig. 8.
2
Advance Information
TEST CONFIGURATION
SL1461SA
BASE BAND VIDEO 1V p-p
TV SAT TEST TX ROHDE & SCHWARZ SFZ
VIDEO GENERATOR ROHDE & SCHWARZ SGPF
RF CARRIER FREQ 479.5MHz FM MODULATION 13.5MHz P-P PRE-EMPHASISED VIDEO
MONTFORD TEST OVEN
SL1461 TEST APPLICATION BOARD See Fig. 3 for details
PRE EMPHASISED BASE BAND VIDEO
VIDEO AMPLIFIER/ DE EMPHASISED NETWORK
DE EMPHASISED BASE BAND VIDEO 1V p-p
VIDEO ANALYSER ROHDE & SCHWARZ UAF
The video drive characteristics measurements were made using the above test configuration. The maximum figures recorded in the Electrical Characteristics Table coincide with high temperatures and extremes of supply voltage. No adjustment to the recorded figures has been made to compensate for the effects of temperature on the external components of the application test board, in particular the varactor diodes. If operation of the device at high ambient temperatures is envisaged then attention to temperature compensation of the external circuitry will result in performance figures closer to the stated typical figures.
Fig.2 SL1461SA block diagram
ABSOLUTE MAXIMUM RATINGS
All voltages are referred to VEE at 0V Characteristics Supply voltage RF input voltage RF input DC offset Oscillator DC offset Video DC offset Video feedback DC offset Video output DC offset AFC pump DC offset AFC disable DC offset AFC deadband DC offset AGC bias DC offset AGC output DC offset Storage temperature Junction temperature MP16 package thermal resistance, chip to ambient -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -55 Min. -0.3 Typ. 7 2.5 VCC+0.3 VCC+0.3 VCC+0.3 VCC+0.3 VCC+0.3 VCC+0.3 VCC+0.3 VCC+0.3 VCC+0.3 VCC+0.3 125 150 111 Max. V Vp-p V V V V V V V V V V C C C/W Conditions
3
SP1461SA
Advance Information
ABSOLUTE MAXIMUM RATINGS cont.
All voltages are referred to VEE at 0V Characteristics MP16 package thermal resistance, chip to case Power consumption at 5.5V ESD protection - pins 1 to 15 ESD protection - Pin 16 2 1.7 Min. Typ. 41 250 Max. C/W mW kV kV Mil-std-883 method 3015 class 1 Mil-std-883 method 3015 class 1 Conditions
2K
AGC BIAS RV1
50K
AFC WINDOW ADJUST RV2 C1 47nF C2 100nF R1
1 2 16 15
100nF 27K R6 C3
47 F C4
+5V 1nF C12
D1 BB515 C5
4K7
TP4 R5 1K2 R4 100pF C11 C10 TP2 VIDEO OUTPUT TP1
3 4
SL1461SA
14 13 12 11 10 9
BB515 470nF D2 TP3 4n7 C6 R2 5K1 4K7 R3 C7 1nF
5 6 7 8
100pF 1K2 C9 47 F C8 1nF
RF INPUT
Fig.3 Standard application circuit
FUNCTIONAL DESCRIPTION
The SL1461SA is a wideband PLL FM demodulator, optimised for application in satellite receiver systems and requiring a minimum external component count. It contains all the elements required for construction of a phase locked loop circuit, with the exception of tuning components for the local oscillator, and an AFC detector circuit for generation of error signal to correct for any frequency drift in the outdoor unit local oscillator. A block diagram is contained in Fig. 2 and the typical application in Fig. 3. The internal pin connections are contained in Fig.6/6a In normal applications the second satellite IF frequency of typically 402 or 479.5MHz is fed to the RF preamplifier, which has a working sensitivity of typically -40 dBm, depending on application and layout. The preamplifier contains an RF level detect circuit, which generates an AGC signal that can be used for controlling the gain of the IF amplifier stages, so maintaining a fixed level to the RF input of the SL1461SA, for optimum threshold performance. The bias point of the AGC circuit can be adjusted to cater for variation in AGC line voltage requirement and device input power. The typical AGC curves are shown in Fig. 9. It is recommended that the device is operated with an input signal between -30 and -35dBm. This ensures optimum linearity and threshold performance, and gives a good safety margin over the typical sensitivity of -40dBm. The output of the preamplifier is fed to the mixer section which is of balanced design for low radiation. In this stage the RF signal is mixed with the local oscillator frequency, which is generatedby an on-board oscillator. The oscillator block uses an external varactor tuned sustaining network and is optimised for high linearity over the normal deviation range. A typical frequency versus voltage characteristic for the oscillator is contained in Fig. 7. The loop output is designed to compensate for first order temperature variation effects; the typical stability is shown in Fig. 8 The output of the mixer is then fed to the loop amplifier around which feedback is applied to determine loop transfer characteristic . Feedback can be applied either in differential or single ended mode; if the appropriate phase detector gains are assumed in calculating loop filters, both modes should give the same loop response. The loop amplifier drives a 75 output impedance buffer amplifier, which can either be connected to a 75 load or used to drive a high input impedance stage giving greater linearity and approximately 6dB higher demodulated signal output level.
4
Advance Information
DESIGN OF PLL LOOP PARAMETERS
R2 C1
SL1461SA
GAIN = KD VOLT/RAD RF INPUT R1
BASEBAND OUTPUT
GAIN = K0 RAD SEC/VOLT VCO
Fig.4
The SL1461SA is normally used as a type 1 second order loop and can be represented by the above diagram. For such a system the following parameters apply;
where: K0 is the VCO gain in radian seconds per volt KD is the phase detector gain in volts per radian n is the natural loop bandwidth is the loop damping factor R1 is loop amplifier input impedance Note: K0 is dependant on sensitivity of VCO used. KD = 0.25V/rad single ended, 0.5V/rad differential
1 2
and K 0K D
1 2 n
From these factors the loop 3dB bandwidth can be determined from the following expression;
2
2 n
AFC FACILITY The SL1461SA contains an analog frequency error detect circuit, which generates DC voltage proportional to the integral of frequency error. If the incident RF is high then the AFC voltage increases, if low then the voltage decreases. The AFC voltage can then be converted by an ADC to be read by the micro controller for frequency fine tuning; if used in an I2C system it is recommended the device is used with either the SP5055 or SP5056 frequency synthesiser which contains an internal ADC readable via the I2C bus. The voltage corresponding to frequency alignment is arbitrary and user defined; if used with the SP5055 it is suggested the aligned voltage is 0.375 VCC , corresponding to the centre code of the ADC on port 6. The AFC detect circuit contains a deadband centre around the aligned frequency. The deadband can be adjusted from zero window to approximately 25MHz width assuming an oscillator dF/dV of 15MHz/V. If the incident RF is within this window the AFC voltage does not integrate, except by component leakage. With reference to Fig.5; in normal operation the demodulated video is fed to a dual comparator where it is
compared with two reference voltages, corresponding to the extremes of the deadband, or window. These voltages are variable and set by the window adjust input. The comparators produce two digital outputs corresponding to voltages above or below the voltage window, or frequency above or below deadband. These digital control signals are used to control a complimentary current source pump. The current signals are then fed to the input of an amplifier which is arranged as an integrator, so integrating the pulses into a DC voltage. If the frequency is correctly aligned both the current source and sink are disabled, therefore the DC output voltage remains constant. There will be a small drift due to component leakage; the maximum drift can be calculated from;
5
SP1461SA
Advance Information
WINDOW ADJUST
V HI VALIGN V LO FREQ VCC VCC + - CEXT BASEBAND VIDEO + - VAFC REXT
VEE
Fig.5 AFC system block diagram
6
Advance Information
SL1461SA
VCC
AGC BIAS
VREF; 2.7V
VREF; 2V
AGC OUTPUT
AGC output
AGC bias adjust
VREF; 3V
AFC WINDOW 2x1500
RF INPUTS
VREF; 1.6V
RF inputs
AFC window adjust
VCC AFC PUMP VIDEO + 10K AFC OUTPUT 330 330 VIDEO -
2mA
2mA
AFC output stage
Video amp outputs
Fig.6 SL1461SA I/O port internal circuitry
7
SP1461SA
Advance Information
VREF; 1.2V 2 x 5k
OSCILLATOR + OSCILLATOR -
Local oscillator
FROM PHASE DETECTOR 2x570
VCC 68
VIDEO OUTPUT
VIDEO FEEDBACK + VIDEO FEEDBACK -
105
4mA
Video amp feedback inputs
Video output drive
Fig.6a SL1461SA I/O port internal circuitry
FREQ MHz 520 500 480 460 440 420 400 360 1 1.5 2 2.5 3 3.5 4 4.5 5 DC VOLTAGE
Fig.7 Typical VCO frequency vs DC control voltage
8
Advance Information
VCO STABILITY vs TEMP and SUPPLY 480 479.5 479 FREQUENCY (MHz) 478.5 478 477.5 477 476.5 476 475.5 -20 5 30 TEMP/C 55 80
SL1461SA
SUPPLY (V) 4.5 4.75 5 5.25 5.5
Fig.8 SL1461SA VCO centre frequency uncompensated temperature stability
2.0
1.5 AGC OUTPUT 1.0 VOLTAGE
AGC BIAS RESISTOR 5.1K AGC BIAS CURRENT 297 A AGC LOAD RESISTOR 3.9K AGC BIAS RESISTOR 10.5K AGC BIAS CURRENT 150 A AGC LOAD RESISTOR 4.7K AGC BIAS RESISTOR 32K AGC BIAS CURRENT 52 A AGC LOAD RESISTOR 10K
0.5
-70
-60
-50
-40
-30
-20
-10
0 VCC = 5.0 VOLTS
RF INPUT LEVEL (dBm) UNMODULATED
Fig.9 SL1461SA AGC output voltage for differing values of AGC bias resistor
APPLICATION NOTES
Capture range Under conditions when there is no RF input signal present, the SL1461SA may react to spurious radiation from the free running oscillator coupling into the RF inputs. Because of the constant phase error between the VCO input to the phase detector and the spuriously coupled signal via the RF input, the phase comparator will drive the control voltage to either the bottom or the top of the range. In such a case, the capture range will be asymmetrical about the VCO free running frequency, since any control voltage will only be able to tune the VCO in one direction if the tuning voltage is already at the max or min. This effect can be avoided by driving the RF input differentially or achieving good common mode rejection to the VCO signal. The lock range is independant of the above effects and will be symmetric about the centre of the phase detector Scurve provided the VCO is correctly aligned. EXAMPLE Loop out of lock Tuning voltage =4.3V (maximum) frequency =520MHz (maximum It is only possible to capture signals below this frequency since the VCO is already at its maximum frequency. Testing of capture range should be done with the device operating under normal conditions. An input signal of between -35dBm to -10dBm is suitable for such a measurement.
9
SP1461SA
Advance Information
The easiest way to centralise the VCO is to input an RF carrier which is being modulated by a low frequency squarewave. The tuning coil(s) should be adjusted until the AFC voltage toggles between 0.2V and VCC-0.7V. The smaller the FM deviation of the squarewave used, the more accurate the setting will be. A pre-emphasised video input containing black to white transitions can also be used for this setting, since the DC content in a pre-emphased video is much less than that in non pre-emphasised video. This is important as any dc content in the input waveform will introduce an offset in the AFC transition point. The setting can be confirmed by measuring the DC voltage on the two video outputs, the voltages should be the same when the oscillator is centred around the incoming frequency. This DC measurement must be carried out with an unmodulated carrier of the required frequency. Modulation must not be present, since by definition, the dc voltages would be changing, thus making accurate measurement difficult.
Lock range Lock range should be symmetric about the centre of the S-curve. When the oscillator is sitting in the centre of the S-curve, the two video outputs will be at the same DC voltage. RF oscillator design The standard application circuit for the SL1461SA is shown in Fig.3 The layout of the VCO tank should follow normal good RF techniques - ie as compact as possible. This will minimise parasitics, thus giving improved VCO linearity and stability. The PCB layout used for testing purpose is shown in Fig. 10. Setting up of oscillator The VCO should be set up so that the desired input RF frequency is at the centre of the lock range. This will coincide with the centre of the S-curve and the point at which the AFC toggles when set to zero deadband.
10
Advance Information
SL1461SA
Fig.10 Layout of demo board with component locations
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