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

ω

τ

)

(

j

τ

τ

π

π

/

f

2

1

f

2

L

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

R3

C2

INPUT

OUTPUT

ω

(a)

R4

1/ 3

τ

1/ 2

τ

m

)

(

j

(b) Amplitude Characteristic

(c) Pole-Zero Diagram

τ

-1/ 2

τ

-1/ 3

R4

R3

R4

m

+

=

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

No

Noise Rejection at Signal Input

PC1

High

PC2 or PC3

Low

AC Ripple Content when PLL is Locked

PC1

PC2

PC3