FS6131

-150°

Frequency (f

-100°

0.1kHz

1kHz

10kHz

100kHz

Figure 9: Loop Nyquist Plot

A Nyquist plot of gain vs. amplitude is shown below.

45°

0°

315°

270°

225°

180°

135°

90°

0.2

0.4

0.6

0.8

1.0

Phase

Amplitude

1.2

Gain Margin

Phase

Margin

Figure 10: Loop Nyquist Plot

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

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