fs6131 AMI Semiconductor, Inc., fs6131 Datasheet - Page 9

• Manufacturer Part Number: fs6131
• Description: Fs6131-01g Programmable Line Lock Clock Generator Ic
• Manufacturer: AMI Semiconductor, Inc.

FS6131-01/FS6131-01g Programmable Line Lock Clock Generator IC
A Nyquist plot of gain vs. amplitude is shown below.
4.4 Voltage-Controlled Crystal Oscillator
The VCXO provides a tunable, low-jitter frequency reference for the rest of the FS6131 system components. Loading capacitance for
the crystal is internal to the device. No external components (other than the resonator itself) are required for operation of the VCXO.
The resonator loading capacitance is adjustable under register control. This feature permits factory coarse tuning of inexpensive
resonators to the necessary precision for digital video applications. Continuous fine-tuning of the VCXO frequency is accomplished by
varying the voltage on the XTUNE pin. The total change (from one extreme to the other) in effective loading capacitance is 1.5pF
nominal, and the effect is shown in Figure 11. The oscillator operates the crystal resonator in the parallel-resonant mode. Crystal
warping, or the "pulling" of the crystal oscillation frequency, is accomplished by altering the effective load capacitance presented to the
crystal by the oscillator circuit. The actual amount that changing the load capacitance alters the oscillator frequency will be dependent
on the characteristics of the crystal as well as the oscillator circuit itself.
The motional capacitance of the crystal (usually referred to by crystal manufacturers as C
and the load capacitance (C
determine the total warping capability of a crystal is
where C
Example: A crystal with the following parameters is used with the FS6131. The total coarse tuning range is:
AMI Semiconductor
www.amis.com
L1
and C
L2
are the two extremes of the applied load capacitance obtained from Table 11.
Specifications subject to change without notice
– Rev. 3.0, Jan. 08
L
) of the oscillator determine the warping capability of the crystal in the oscillator circuit. A simple formula to
Amplitude
180°
C
∆
Margin
Phase
∆
1
f
=0.02pF, C
f
=
(
135°
225°
ppm
0
2
.
02
×
(
Gain Margin
)
5
Figure 10: Loop Nyquist Plot
×
=
0
+
(
=5.0pF, C
22
2
22
×
.
66
C
.
66
(
C
9
1
×
−
) (
0
×
Phase
10
(
L1
+
270°
C
90°
=10.0pF, C
1.2
1.0
0.8
0.6
0.4
0.2
5
C
)
L
×
+
2
L
10
−
2
10
) (
C
×
6
)
L
=
1
C
)
L2
×
305
0
=22.66pF
+
10
C
ppm
6
L
45°
315°
1
)
1
), the static capacitance of the crystal (C
0°
Data Sheet
0
)