U74HC4046AL-S16-R datasheet(17/19 Pages) UTC

17 / 19 page

U74HC4046A

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

17 of 19

www.unisonic.com.tw

QW-R502-461.C

APPLICATION INFORMATION(Cont.)

PLL Frequency Capture Range

(Phase comparator: PC1, PC2 or PC3)

Loop filter component selection

)

(

F ω

A small capture range (2fC) is obtained if

C ≈

Fig.13 Simple loop ﬁlter for PLL without offset; R3 ≥ 500 Ω.

INPUT

OUTPUT

(a)

1/ 3

1/ 2

)

(

F ω

(b) Amplitude Characteristic

τ1 = R3 × C2

τ2 = R4 × C2

τ 3 = (R3 + 4)× C2

-1/ 2

-1/ 3

Fig.14 Simple loop ﬁlter for PLL with offset; R3 + R4 ≥ 500 Ω.

Subject

Phase comparator Design considerations

PLL Locks on Harmonics at Centre Frequency

PC1 or PC3

Yes

PC2

Noise Rejection at Signal Input

PC1

High

PC2 or PC3

Low

AC Ripple Content when PLL is Locked

PC1

fr = 2fi, large ripple content at φDEMOUT = 90°

PC2

fr = fi, small ripple content at φDEMOUT = 0°

PC3

fr = fi, large ripple content at φDEMOUT = 180°

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