section - Bitsavers

More documents

Recommendations

Info

PHASE LOCKED LOOP APPLICATIONSbaud or bits per second, or 150Hz) and twice the inputfrequency (about 2200Hz). The free-running frequencyshould be adjusted (with R 1) so that the dc voltage level atthe output is the same as that at pin 6 of the loop. Theoutput signal can now be made logic compatible byconnecting a voltage comparator between the ,output andpin 6.The input connection is typical for cases where a dc voltageis present at the source and, therefore, a direct connectionis not desirable. Both input terminals are returned toground with identical resistors (in this case, the values arechosen to achieve a 600n input impedance.)FSK DECODER WITH EXPANDED565 OUTPUT VOLTAGE RANGEV,:z+14VFor best operation, the free-running veo frequency shouldbe adjusted so that the output voltage (corresponding tothe input frequencies of 1070Hz and 1270Hz swingsequally to both sides of the reference voltage at pin 6. Thiscan be easily done by adjusting the center frequency of theveo so that the output signal of the 5710 comparator hasa 50% duty cycle. It is usually necessary to decouple pin 6with a large capacitor connected to the positive supply inorder to obtai n a stable reference voltage for the 5710comparator.Figure 8-54 shows the output of the 5710 comparator andthe output of the 565 phase locked loop after the filter atrates of 100,200 and 300 baud, respectively.100 BAUD FSK DECODINGINPUTo---}r-.--f---IOUTPUTFigure 8-53A more sophisticated approach primarily useful for narrowfrequency deviations is shown in Figure 8-53. Here, aconstant current is injected into pin 8 by means oftransistor 01. This has the effect of decreasing the lockrange and increasing the output voltage sensitivity to theinput frequency shift. The basis for this scheme is the factthat the output voltage (control voltage for VeO) controlsonly the current through R 1, while the current through 01remains constant. Thus, if most of the capacitor chargingcurrent is due to 01, the current variation due to R 1 willbe a small percentage of the total charging current and,consequently, the total frequency deviation of the veowill be limited to a small percentage of the centerfrequency. A 0.25mfd loop filter capacitor gives approximately30% overshoot on the output pulse, as seen in theaccompanying photographs.The output is then filtered with a two-stage Re ladderfilter with a band edge chosen to be approximately 800Hz(approximately half-way between the maximum keyingrate of 150Hz and twice the carrier frequency). Thenumber of stages on the filter can be more or lessdepending on the degree of uncertainty allowable in thecomparator output pulse. Two small capacitors (typically0.001 mfd) are connected between pins 8 and 7 of the 565and across the input of the comparator to avoid possibleoscillation problems.Figure 8-54a200 BAUD FSK DECODINGFigure 8-54b300 BAUD FSK DECODIN.GF~gure 8-54c57
PHASE LOCKED LOOP APPLICATIONSANALOG LIGHT-COUPLED ISOLATORS (565,567)The analog isolator shown in Figure 8-55a is basically aFM transmission system with light as the transmissionmedium. Because of the high degree of electrical isolationachieved, low-level signals may be transmitted withoutinterference by great potential difference between thesending and receiving circuits. The transmitter is a 565used as a veo with the input applied to the veo terminal7. Since the light emitting diode is driven from the 565veo output, the LED flashes at a rate proportional to theinput voltage. The receiver is a photo transistor whichdrives an amplifier having sufficient gain to apply a 200mVpeak-to-peak signal to the input of the receiving 565,which then acts as a FM detector with the output appearingat pin 7. Since the output has a twice carrier frequencyripple, it is best to keep the carrier frequency as high aspossible (say, 100 times the highest modulation frequency).Because of the excellent temperature stability of the 565,drift is minimal even when dc levels are being transmitted.If operation to dc is not required, the output of the receivercan be capacitively coupled to the next stage. Also, a 566can be used as the transmitter.LIGHT-COUPLED ANALOG ISOLATORS+V +V +v +V +V~ 10INPUT7 565 4 t--I~+-'£OUTPUTDC LEVELADJUST'::"'-V -V -v -V~OUTPUTIFILTER CAP.Figure 8-55aFigure 8-55b shows that the 567 may be used in the samemanner when operation from 5V supplies is required. Here,the output stage of the 567 is used to drive the LEDdirectly. When the free-running frequency of the receiving567 is the same as that of the transm itting 567, thenon-linearity of the two controlled oscillator transferfunctions cancel so that highly linear information transferresults.LIGHT-COUPLED ANALOG ISOLATORS+5 +5+5OUTPUTDC LEVELADJUSTFigure 8-55b58
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 42 and 43: PHASE LOCKED LOOP APPLICATIONSSCHEM
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 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
show all

section - Bitsavers

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?