XR-2212_06 Datasheet, PDF (13/20 Pages) Exar Corporation – Precision Phase-Locked Loop

XR-2212
frequencies is desired, set f₀ to be at mid-point of the
desired range.
b) Choose timing resistor R₀ to be in the range of 15kW
to 100kW. This choice is arbitrary. R₀ can be fine
tuned with a series potentiometer, R_X.
c) Choose timing capacitor, C₀ from Figure 7 or
Equation 1.
d) Calculate R₁ to set tracking bandwidth (see
Figure 10 and design equation 5). If a range of output
frequencies are desired, set R₁ to get:
Df = f_max - f_min
If a single fixed output frequency is desired, set R₁ to
get:
Df = 0.1 f₀
e) Calculate C₁ to obtain desired loop damping. (See
design equation 4). For most applications, ς = 1/2 is
recommended, thus:
C₀ = NC₀/4
Note
All component values except R₀ can be rounded off to the
nearest standard value.
2
Input
Signal
0.1mF
4
Output
F1 = Nfs
V_CC
0.1mF
Phase
Detector
16
10
C₁
1 _VCC
9
7
%N
F_O= F1/N
5
1K
74LS90
or
Similar
VCO
R₁
12
14
13
R₀
C_O
11
0.1mF
6
8
Internal
Reference
Figure 12. Circuit Connection for Frequency Synthesizer
Rev. 2.10
13