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PHASE LOCKED LOOP APPLICATIONSSCHEMATIC DIAGRAM OF 567R3 :'.7' r? +C3CURRENT CONTROLLEDOSCILLATORQUADRATUREPHASE DETECTORFigure 8-34A doubly-balanced multiplier formed by 032 through037 (Figure 8-34)" functions as the phase detector. Theinput signal is applied to the base of Q32. Transistors034 - Q37 are driven by a square wave taken from theCCO at the collector of Q2. Phase detector input bias isprovided by three diodes, Q38 through Q40, connected inseries, assuring good bias voltage matching from run to run.Emitter resistors R26 and R27, in addition to providingthe necessary dynamic range at the input, help stabilize thegain over the wide temperature range.The loop dc amplifier is formed by 051 and Q52. Havinga current gain of 8, it permits even a small phase detectoroutput to drive the CCO the full ±7%. Therefore, fulldetection bandwidth can be obtained for any in-band inputsignal greater than about 70mV rms. However, the mainpurpose of high loop gain in the tone decoder is to keepthe locked phase as close to 1f /2 as possible for all but thesmallest input levels since this greatly facilitates operationof the quadrature lock detector. Emitter resistors R36 andR37 help stabilize the gain over the required temperaturerange. Another function of the dc amplifier is to allow ahigher impedance level at the low pass filter terminal(pin 2) so that a smaller capacitor can be used for a givenloop cutoff frequency. Once again, emitter resistors helpstabilize the loop gain over the temperature range.The quadrature phase detector (QPO), formed by a seconddoubly-balanced mUltiplier Q42 - Q47, is driven from thequadrature output (E, F, in Figure 8-34) of the CCO. Thesignal input comes from the emitters of the inputtransistors Q32 and 033·The output stage, Q53 through 062, compares the averageOPO current in the low pass output filter R3C3 with atemperature compensated current in R39 (forming thethreshold voltage V t).Since R3 is slightly lower in value than R39, the outputstage is normally off. When the lock and the OPO currentIq occurs, pin 1 voltage drops below the threshold voltageV t and the output stage is energized.The uncommitted collector (pin 8) of the power npnoutput transi~tor can drive both 100 - 200mA loads andlogic elements, including TTL.41
PHASE LOCKED LOOP APPLICATIONSEXPANDING LOOP CAPABILITYLOW PASS FILTER CIRCUITS (560B, 561B and 562B)The low pass filters used with the 560B, 561 Band 562Bare externally adjusted to provide the desired operationalcharacteristics. To select the most appropriate type of filterand component values, a basic understanding of filteroperation is required.A FM signal to be demodulated is matched in the phasecomparator with the voltage controlled oscillator signal,which is tuned to the FM center frequency. Anyresulting phase difference between these two signals is thedemodulated FM signal, This demodulated signal isnormally at frequencies between dc and upper audiofrequencies.The choice of Iqw pass filter response gives a degree ofdesign freedom in determining the capture range orselectivity of the loop. The attenuation of the highfrequency error components at the output of the phasedetector enhances the interference rejection characteristicsof the loop. The filter also provides a short-term memoryfor the PLL that ensures rapid recapture of the signal if thesystem is thrown out of lock due to a noise transient.To ensure absolute closed loop stability at all signal levelswithin the dynamic range of the loop, the open loop PLL isrequired to have no more than 12dB per octaVe highfrequency roll-off.The capacitor in each filter circuit shown in Figure 8-35will provide 6dB per octave roll-off at the first breakpoint-the desired bandwidth frequency. The resistance Rxshown in filters (c) and (d) is used to break the response upat high frequencies to ensure 6dB per octave roll-off at theloop unity gain frequency. Rx is typically between 50 and200[2.Calculation of values for low pass filters shown can bemade using the complex second-degree transfer functionequations given, or approximated using the equation:2660C1 = -- mfd for filters (a) and (c), and the equation:f1330C1 = --mfd for filters (b) and (d) where f is the desiredffirst break frequency in Hz.At frequencies greater than 5M Hz where the loop may beprone to instability, filters (a) and (c) should be used. Foroperation at low frequencies, a simple type (b) lag filterwith no added resistance is usually sufficient.OPERATING FREQUENCY EXTENSION TO 60MHz(560B, 561 B, 562B)The frequency range of the 560B, 561 Band 562B phaselocked loops may be extended to 60MHz by the additionof two 10K n resistors from the timing capacitor terminalsto the negative power supply as shown in Figure 8-36. Theinclusion of a 5K n potentiometer between these 10K nresistors and the negative supply provides a simple methodof fine tuning.OPERATING FREQUENCY EXTENSIONFOR 560B, 561B AND 562B5608561856288 (5) 2 (6) 3Co10K10KUSE PINS (5) & (6) FOR 56285608561856288 (5) 2 (6) 3-=LOW PASS FILTER CONFIGURATIONSFigure 8-36(R = INTERNALRESISTANCE = 6Kn)INCREASED LOOP OUTPUT VOLTAGE FOR SMALLFREQUENCY DEVIATIONS (565)F(s) =HsRxC,Hs(Rx+R)C,1F(s) = HsRC,Figure 8-35_ HsRXC,F(s) - '+(2R+RX)C,C,1F(s) = H2sRC,For applications where both a narrow lock range and alarge output voltage swing are required, it is necessary toinject a constant current into pin 8 and increase the valueof R1' One scheme for this is shown in Figure 8-37. Thebasis for this scheme is the fact that the output voltagecontrols only the current through R 1 while the currentthrough Q1 remains constant. Thus, if most of the chargingcurrent is due to 01, the total current can be varied only asmall amount due to the small change in current throughR 1. Consequently, the VCO can track the input signal overa small frequency range yet the output voltage of the loop(control voltage of the VeO) will swing its maximum value.42
Page 2 and 3: TABLE OF CONTENTSSECTION TITLE PAGE
Page 4: SECTIONINTRODUCTIONPHASE LOCKED LOO
Page 7 and 8: USER'S QUICK-LOOK GUIDE TO SIGNETIC
Page 10: SECTIONTHE PHASE LOCKED LOOP PRINCI
Page 13 and 14: PHASE LOCKED LOOP APPLICATIONSIt is
Page 15 and 16: PHASE LOCKED LOOP APPLICATIONSROOT
Page 17 and 18: PHASE LOCKED LOOP APPLICATIONSINTEG
Page 19 and 20: ~PHASE LOCKED LOOP APPLICATIONSFUNC
Page 21 and 22: PHASE LOCKED LOOP APPLICATIONSFREQU
Page 24 and 25: PHASE LOCKED LOOP APPLICATIONSGENER
Page 26 and 27: PHASE LOCKED LOOP APPLICATIONSPROBA
Page 28 and 29: ~PHASE LOCKED LOOP APPLICATIONSCapt
Page 30 and 31: PHASE LOCKED LOOP APPLICATIONSTRANS
Page 32 and 33: PHASE LOCKED LOOP APPLICATIONSThe V
Page 34 and 35: PHASE LOCKED LOOP APPLICATIONSINTER
Page 36 and 37: PHASE LOCKED LOOP APPLICATIONSIt is
Page 38 and 39: PHASE LOCKED LOOP APPLICATIONSWhen
Page 40 and 41: PHASE LOCKED LOOP APPLICATIONSSIMPL
Page 44 and 45: PHASE LOCKED LOOP APPLICATIONSNARRO
Page 46 and 47: PHASE LOCKED LOOP APPLICATIONSTwo e
Page 48: PHASE LOCKED LOOP APPLICATIONSd.)e.
Page 52 and 53: PHASE LOCKED LOOP APPLICATIONSFM IF
Page 54 and 55: PHASE LOCKED LOOP APPLICATIONSPHASE
Page 56 and 57: PHASE LOCKED LOOP APPLICATIONSTRANS
Page 58 and 59: PHASE LOCKED LOOP APPLICATIONSbaud
Page 60 and 61: PHASE LOCKED LOOP APPLICATIONSFigur
Page 62 and 63: PHASE LOCKED LOOP APPLICATIONSinput
Page 64 and 65: PHASE LOCKED LOOP APPLICATIONfTRIAN
Page 66 and 67: PHASE LOCKED LOOP APPLICATIONSRF-FM
Page 68 and 69: PHASE LOCKED LOOP APPLICATIONSVHF O
Page 70 and 71: PHASE LOCKED LOOP APPLICATIONSPRECI
Page 72 and 73: PHASE LOCKED LOOP APPLICATIONSFSK D
Page 74 and 75: PHASE LOCKED LOOP APPLICATIONSThe c
Page 76 and 77: PHASE LOCKED LOOP APPLICATIONSFLUTT
Page 78 and 79: PHASE LOCKED LOOP APPLICATIONSSALES
Page 80 and 81: PHASE LOCKED LOOP APPLICATIONSINTER

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