EL4585C
Horizontal Genlock 8 F
SC
Applications Information
Choosing External Components
1 To choose LC VCO components first pick the
desired operating frequency For our example
we will use 28 636MHz with an H-sync fre-
quency of 15 734kHz
2 Choose a reasonable inductor value (1-5mH
works well) We choose 3 3mH
3 Calculate C
T
needed to produce F
OSC
1
F
OSC
e
2
q
0
LC
T
1
1
e
e
9 4pF
C
T
e
4
q
2
F
2
L 4
q
2
(28 636e6)
2
(3 3e
b
6)
2 5V
4 From the varactor data sheet find C
V
e
23pF for our
the desired lock voltage C
V
SMV1204-12 for example
5 C
2
should be about 10C
V
so we choose
C
2
e
220pF for our example
6 Calculate C
1
Since
C
T
e
then
C
1
e
C
2
C
T
C
V
(C
2
C
v
)
b
(C
2
C
T
)
b
(C
T
C
V
)
C
1
C
2
C
V
(C
1
C
2
)
a
(C
1
C
V
)
a
(C
2
C
V
)
4585 – 10
Typical LC VCO
LC VCO Component Values (Approximate)
Frequency
(MHz)
26 602
27 0
29 5
35 468
21 476
24 546
28 636
L1
(mH)
33
33
27
22
47
39
33
C1
(pF)
22
21
22
16
26
22
17
C2
(pF)
220
220
220
220
220
220
220
Note Use shielded inductors for optimum performance
Typical Xtal VCO
For our example C
1
e
17pF (A trim cap may be
used for fine tuning ) Examples for each frequen-
cy using the internal divider follow
4585 – 11
8
ELANTEC [ ELANTEC SEMICONDUCTOR ]
