el4584 Intersil Corporation, el4584 Datasheet - Page 10

• Manufacturer Part Number: el4584
• Description: Horizontal Genlock, 4fsc
• Manufacturer: Intersil Corporation

Where:
It can be shown that for the loop filter shown below:
C
Where ϖ
factor.
N
We choose R
1. K
2. The loop bandwidth should be about H
3. N = 910 from table 1.
4. K
5. Now we can solve for C
6. Notice R
3
K
F(s) = loop filter impedance in V/A
K
N = internal or external divisor
=
=
d
VCO
frequency/20, and the damping ratio should be 1 for
optimum performance. For our example,
ϖ
for each volt applied at the control pin. It is assumed (but
probably is not) linear about the lock point (2.5V). Its
value depends on the VCO configuration and the varactor
transfer function C
bias control voltage, and C
Since F(V
VCO and measure K
such measurement are shown below. The slope of the
curve is determined by linear regression techniques and
equals K
should be large, around 100k, and can be adjusted to
compensate for any static phase error Tθ at lock, but if
made too large, will slow loop response. If R
smaller, Tθ (see timing diagrams) increases, and if R
----------------------------------------------------------
H SYNCfrequency
= phase detector gain in A/rad
d
VCO
n
K
----------------------- - C
–
d
VCOfrequency
= 300µA/2πrad = 4.77e-5A/rad for the EL4584.
= 15.734kHz/20 = 787Hz≈5000rad/S.
Nω
K
= VCO gain in rad/s/V
n
VCO
represents how much the VCO frequency changes
= loop filter bandwidth, and ζ = loop filter damping
2
n
2
VCO
3
,
C
F
has little effect on the loop filter design. R
) is nonlinear, it is probably best to build the
OSC
= 30kΩ for convenience.
4
. For our example, K
=
vs V
C
------ - R
10
C
3
V
, LC VCO
,
= F(V
VCO
=
3
=
14.31818M
----------------------------- -
3
15.73426k
10
, C
----------------------- -
K
about 2.5V. The results of one
C
2Nξω
V
d
), where V
4
K
is varactor capacitance.
, and R
VCO
n
VCO
=
3
910
.
C
SYNC
= 6.05 Mrad/S/V.
is the reverse
2
is made
2
2
EL4584
Lock Time
Let = R
lock time. Decreasing T decreases damping and speeds up
loop response, but increases overshoot and thus increases
the number of hunting oscillations before lock. Critical
damping (ζ = 1) occurs at minimum lock time. Because
decreased damping also decreases loop stability, it is
sometimes desirable to design slightly overdamped (ζ > 1),
trading lock time for increased stability.
FREQUENCY
increases, Tθ decreases. For LDET to be low at lock,
|Tθ| < 50 ns. C
frequency noise from the charge pump.
13.301
17.734
10.738
12.273
14.318
(MHZ)
14.75
13.5
C
C
R
LC LOOP FILTER COMPONENTS (APPROXIMATE)
3
3
4
3
C
=
=
=
3
. As T increases, damping increases, but so does
K
----------------------- -
C
------ -
10
----------------------- -
K
2Nζω
d
d
3
Nω
FIGURE 7. TYPICAL LOOP FILTER
K
K
=
VCO
VCO
2
n
0.0001µF
n
(kΩ)
4
100
100
100
100
100
100
100
R
is used mainly to attenuate high
2
=
=
(
----------------------------------------------------- -
----------------------------------------------------- -
(
2 ( ) 910
4.77e 5
4.77e 5
(
(
910
–
–
(kΩ)
) 5000
R
30
30
33
39
22
27
30
) 1 ( ) 5000
(
3
) 6.05e6
) 6.05e6
(
(
(
)
2
)
)
)
0.01
0.01
0.01
0.01
0.01
0.01
0.01
(µF)
C
=
=
3
0.01µF
31.5kΩ
July 25, 2005
0.001
0.001
0.001
0.001
0.001
0.001
0.001
(µF)
C
FN7174.2
4