Costas Loop oscillates in ModelSim while locks in MATLAB!

Honored Contributor

11 years ago

Hello Mr Kazem,

I did the test you suggested... maybe results are disappointing.

These are all with a single tone input.

With a small amount of scaling... loop takes some time:

Without scaling:

I don't know if the latter gonna lock eventually. What to do now?

By the way, I found a bug in my code... the loop filter is clocked by a 50 MHz, and its input is the phase detector (multiplier) which in turn

has RRCs as input, the RRCs produce a sample every several clock cycles of the 50 MHz... I thought it would be the problem.

I made an enable port for the Loop Filter so it only works when a new sample comes out of the RRCs. However, nothing changed... but I think

this is how it should be.

** UPDATE **

This is the output of the loop filter for 1 ms.

I and Q are sinusoidal signals!! This never gonna lock!! :'(

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