U74HC4046AL-S16-R datasheet(16/19 Pages) UTC

16 / 19 page

U74HC4046A

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

16 of 19

www.unisonic.com.tw

QW-R502-461.C

APPLICATION INFORMATION(Cont.)

VCO Frequency with Extra Offset

(Phase Comparator: PC1, PC2 or PC3)

Frequency characteristic:

With R1 and R2 between 3 kΩ and 300 kΩ, the characteristics of the VCO operation will be as shown in Fig.12.

due to R1, C1

fVCO

fMAX

fMIN

½ VCC

VCC–0.9V

VCC

VCOIN

0.9V

2fL

fOFF

due to R2, C1

Fig.12 Frequency characteristic of VCO operating with offset:

f0 = centre frequency; 2fL = frequency lock range.

PC1, PC2 or PC3

Selection of R1, R2 and C1

Given fo and fL, determine the value of R1×C1

Calculate fOFF from the equation fOFF = fO – 1.6fL

Obtain the values of C1 and R2

Calculate the value of R1 from the value of C1 and R1×C1.

Subject

Phase comparator

Design considerations

PLL Conditions with no

Signal at the SIGIN Input

PC1

VCO adjusts to fo with φDEMOUT = 90° and VVCONIN = 1/2 VCD (Fig.1).

PC2

VCO adjusts to fo with φDEMOUT = -360° and VVCONIN = min. (Fig.3).

PC3

VCO adjusts to fo with φDEMOUT = -360° and VVCONIN = min. (Fig.5).

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