PLL question

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Hi, I have a 1GHz PLL and the voltage at the output of the phase detector + charge pump block is too high. Any ideas what may be wrong? thanks

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It probably means that the PLL cannot lock. There are a number of possibilities.

1. If the VCO is partially tuned by external components, they may be incorrect.

2. The loop divider is incorrectly programmed

3. The reference divider is incorrectly programmed.

4. If it a PLL with an external VCO, check that you have the loop polarity correct. This is used to correct for the tuning sense of the VCO. Some VCOs have high control input for high output frequency; others have low control input for high output frequency.

Many PLL chips have an output to monitor the the output of the loop divider or the reference divider to verify that those are at the correct frequencies. If your PLL has either of these outputs, it is worthwhile to use them.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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ok that gives me a starting point. Thanks for your suggestions,Jim. I will let you know what I find.