EL4584C
Horizontal Genlock 4 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 14 31818 MHz with an H-sync fre-
quency of 15 734 kHz
2 Choose a reasonable inductor value (10–20mH
works well) We choose 15
mH
3 Calculate C
T
needed to produce F
OSC
F
OSC
e
C
T
e
1
2
q
0
LC
T
Typical LC VCO
4584 – 10
Figure 10
LC VCO Component Values (Approximate)
Frequency
(MHz)
13 301
13 5
14 75
17 734
10 738
12 273
14 318
L1
(mH)
15
15
12
12
22
18
15
C1
(pF)
18
17
18
10
20
17
14
C2
(pF)
220
220
220
220
220
220
220
1
1
e
e
8 2 pF
4
q
2
F
2
L 4
q
2
(14 318e6)
2
(15e
b
6)
2 5V
4 From the varactor data sheet find C
V
the desired lock voltage C
V
e
23 pF for our
SMV1204-12 for example
5 C
2
should be about 10C
V
so we choose
C
2
e
220 pF for our example
6 Calculate C
1
Since
C
1
C
2
C
V
C
T
e
(C
1
C
2
)
a
(C
1
C
V
)
a
(C
2
C
V
)
then
C
1
e
C
2
C
T
C
V
(C
2
C
V
)
b
(C
2
C
T
)
b
(C
T
C
V
)
Note Use shielded inductors for optimum performance
Typical Xtal VCO
For our example C
1
e
14 pF (A trim cap may be
used for fine tuning ) Examples for each frequen-
cy using the internal divider follow
Typical Application
Horizontal genlock provides clock for an analog
to digital converter digitizing analog video
4584 – 11
Figure 11
4584 – 18
9
ELANTEC [ ELANTEC SEMICONDUCTOR ]
