74HC4046A Datasheet, PDF (25/34 Pages) NXP Semiconductors – Phase-locked-loop with VCO

Philips Semiconductors
Phase-locked-loop with VCO
Product specification
74HC/HCT4046A
APPLICATION INFORMATION
This information is a guide for the approximation of values of external components to be used with the 74HC/HCT4046A
in a phase-lock-loop system.
References should be made to Figs 29, 30 and 31 as indicated in the table.
Values of the selected components should be within the following ranges:
R1
between 3 kΩ and 300 kΩ;
R2
between 3 kΩ and 300 kΩ;
R1 + R2 parallel value > 2.7 kΩ;
C1
greater than 40 pF.
SUBJECT
PHASE
COMPARATOR
VCO frequency
without extra
offset
PC1, PC2 or PC3
DESIGN CONSIDERATIONS
VCO frequency characteristic
With R2 = ∞ and R1 within the range 3 kΩ < R1 < 300 kΩ, the
characteristics of the VCO operation will be as shown in Fig.25.
(Due to R1, C1 time constant a small offset remains when R2 = ∞.).
PC1
PC2 or PC3
Fig.25 Frequency characteristic of VCO operating without offset:
f₀ = centre frequency; 2f_L = frequency lock range.
Selection of R1 and C1
Given f_o, determine the values of R1 and C1 using Fig.29.
Given f_max and f_o, determine the values of R1 and C1 using Fig.29, use
Fig.31 to obtain 2f_L and then use this to calculate f_min.
1997 Nov 25
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