U74HCT7046L-P16-R datasheet(10/16 Pages) UTC

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U74HCT7046

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

10 of 16

www.unisonic.com.tw

QW-R502-851.A

PHASE COMPARATORS (Cont.)

Phase comparator 2 (PC2)

This is a positive edge-triggered phase and frequency detector. If the PLL is using the comparator, the loop is

controlled by positive signal transitions and the duty factors of SIGIN and COMPIN are not important. PC2 is

comprised of two D-type flip-flops, control-gating and a 3-state output stage. The circuit function is as an up-down

counter (Logic Diagram) for SIGIN causes an up-count and COMPIN causes a down-count.

The transfer function of PC2, assuming ripple (fr = fi) is suppressed, is

)

(

COMPIN

SIGIN

DEMOUT

−

where VDEMOUT is the demodulator output at pin 10; VDEMOUT = VPC2OUT (via low-pass filter).

The phase comparator gain is:

)

V /

(

As shown in Fig.3, VDEMOUT is the resultant of the initial phase differences of SIGIN and COMPIN. Typical

waveforms for the PC2 loop locked at fo are shown in Fig.4.

Fig.3 Phase comparator 2: average output voltage versus input phase difference.

Fig.4 Typical waveforms for PLL using phase comparator 2, loop locked at fo.

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