December 1990 28
Philips Semiconductors Product specification
Phase-locked-loop with lock detector 74HC/HCT7046A
VCO frequency characteristic
VCO frequency
with extra
offset
PC1, PC2 With R1 and R2 within the ranges 3 kΩ< R1 < 300 kΩ, 3 kΩ<R2 < 300 kΩ,
the characteristics of the VCO operation will be as shown in Fig. 24.
Fig. 24 Frequency characteristic of VCO operating with offset:
f
o
= centre frequency; 2f
L
= frequency lock range.
Selection of R1, R2 and C1
PC1, PC2 Given f
0
and f
L
, determine the value of product R1C1 by using Fig.29.
Calculate f
off
from the equation f
off
=f
o
−1.6f
L
.
Obtain the values of C1 and R2 by using Fig.28.
Calculate the value of R1 from the value of C1 and the product R1C1.
SUBJECT
PHASE
COMPARATOR
DESIGN CONSIDERATIONS