520 Chapter10
Synthesizer Section
General PLL Troubleshooting
General PLL Troubleshooting
The synthesizer section relies heavily on phase-locked loops (PLL).
Typically, faulty PLLs are either locked at the wrong frequency or
unlocked. The information below applies to troubleshooting these two
classes of problems on a generalized PLL.
PLL Locked at Wrong Frequency
Numbers in the following text identify items in Figure 10-5 on page
521.
• Any frequency errors at reference (1) will be multiplied by N/M on
the PLL output.
• A sampler reference-frequency error (2) will be multiplied by its
harmonic on the PLL output.
• A mixer reference-frequency error (3) produces the identical error on
the PLL output.
• If divider input or output frequencies (4) are wrong, check for
incorrect divide numbers and data controlling the dividers.
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