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PHASE LOCKED LOOP APPLICATIONSSCHEMATIC DIAGRAM OF 566+vl R1~(EXT) 6I5VCo-........ --C8~----~-'--------~--~------~--1---~------1-~V+Rg~------~---------+---+------~------~~--~~------~~----~--o1GNDCURRENT SOURCE VCo SCHMITT TRIGGERFigure 8-31DETAILED DESCRIPTION OF 567The 567 is a PLL designed specifically for frequencysensing or tone decoding. Like the 561, the 567 has acontrolled oscillator, a phase detector and a secondauxiliary or quadrature phase detector. In addition,however, it contains a power output stage which is drivendirectly by the quadrature phase detector output. Duringlock, the quadrature phase detector drives the outputstage on, so the device functions as a tone decoder orfrequency relay. The tone decoder center frequency andbandwidth are specified by the center frequency andcapture range of the loop portion. Since a tone decoder,by definition, responds to a stable frequency, the lock ortracking range is relatively unimportant except as it limitsthe maximum attainable capture range.The current controlled oscillator is shown in simplifiedform in Figure 8-32. It provides both a square waveoutput and a quadrature output. The control current Icsweeps the oscillator ±7% of the center frequency, which isset by external components R 1 and C1. It operates asfollows:Transistors Q1 through Q6 form a flip-flop which canswitch pin 5 between Vbe and V+ - Vbe. Thus, the R1C1network is driven from a square wave of V+ - 2V bepeak-to-peak volts. On the positive portion of the squarewave, Cl is charged through R 1 until V 1 is reached. Acomparator circuit driven from Cl at pin 6 then supplies apulse which resets the flip-flop so that pin 5 switches toVbe and Cl is discharged until V2 is reached. A secondcomparator then supplies a pulse which sets the flip-flopand Cl resumes charging.38