EL4584C Elantec Semiconductor, Inc. (acquired by Intersil), EL4584C Datasheet - Page 10

• Manufacturer Part Number: EL4584C
• Description: Horizontal Genlock, 4FSC
• Manufacturer: Elantec Semiconductor, Inc. (acquired by Intersil)

The above oscillators are arranged as Colpitts os-
cillators and the structure is redrawn here to em-
phasize the split capacitance used in a Colpitts
oscillator It should be noted that this oscillator
configuration is just one of literally hundreds
possible and the configuration shown here does
not necessarily represent the best solution for all
applications Crystal manufacturers are very in-
formative sources on the design and use of oscil-
lators in a wide variety of applications and the
reader is encouraged to become familiar with
them
C
lates the control from the oscillator and V1 is the
primary control device C
than C
capability The frequency of oscillation is given
by
F
C
EL4584C
Horizontal Genlock 4 F
1
T
Xtal VCO Component Values (Approximate)
e
Frequency
is to adjust the center frequency C
e
2
(MHz)
13 301
13 5
14 75
17 734
10 738
12 273
14 318
(C
V
1
LC
1
C
so that V
2
T
)
a
Colpitts Oscillator
C
(C
1
C
1
1
C
2
(k )
300
300
300
300
300
300
300
C
R1
V
has maximum modulation
)
V
a
2
should be much larger
(C
2
C
(pF)
C1
V
15
15
15
15
15
15
15
)
SC
2
DC iso-
(uF)
C2
001
001
001
001
001
001
001
4584 – 12
10
Choosing Loop Filter
Components
The PLL VCO and loop filter can be described
as
Where
K
F(s)
K
N
It can be shown that for the loop filter shown
below
C
Where
filter damping factor
1 K
2 The loop bandwidth should be about H-sync
3 N
N
4 K
3
d
VCO
e
EL4584C
frequency 20 and the damping ratio should be
1 for optimum performance For our example
cy changes for each volt applied at the control
pin It is assumed (but probably isn’t) linear
about the lock point (2 5V) Its value depends
on the VCO configuration and the varactor
e
e
e
d
n
VCO
internal or external divisor
e
e
phase detector gain in A rad
H-SYNCfrequency
K
e
e
e
loop filter impedance in V A
910 from table 1
d
VCOfrequency
N
VCO gain in rad s V
K
n
15 734 kHz 20
represents how much the VCO frequen-
300
VCO
e
2
n
loop filter bandwidth and
A 2 rad
C
4
e
C
10
3
e
e
e
R
3
787 Hz
14 31818M
15 73426k
4 77e-5A rad for the
e
K
2N
d
K
VCO
5000 rad S
n
e
910
e
4584 – 13
loop