pll output is just single dc line and no oscillation

I have used "Integer N PLL with Single Modulus Prescaler" on simulink to simulate the PLL time domain output but it gives my single DC line as output and no oscillation. I thought my setting might be incorrect so I put the same setting for the pll video on matlab youtube channel but the result is the same

Answer 1

[Sudarsanan A K]

Hi Ahmad,

If you are observing a single DC line as the output in your Simulink PLL simulation without any oscillation, it likely means the PLL has successfully locked to the input signal. To troubleshoot and potentially observe transient behaviors or oscillations:

• Re-evaluate Initial Conditions: Adjust the simulation to start from a non-locked state or introduce a disturbance.
• Vary Input Signal Characteristics: Change the input signal's frequency or phase abruptly to challenge the PLL's locking mechanism.
• Adjust PLL Configuration: Fine-tune loop filter settings and VCO frequency range to modify the system's response time and stability.
• Verify Prescaler Configuration: Ensure the prescaler's division ratio is correctly set for the desired input frequency range.
• Employ Diagnostic Tools: Use simulation scopes to monitor various points within the PLL loop, providing insight into its behavior throughout the locking process.

Adjusting these factors should help in observing the expected oscillations or transient behaviors in your PLL simulation.

For a practical reference on designing and evaluating a simple PLL model in Simulink, you might find this example helpful:

https://mathworks.com/help/msblks/gs/DesignAndEvaluateSimplePLLModel.html

I hope this helps!

[ahmad jadery]

thanks Sudarsanan A K for your reply

i applaied your suggessts but no oscillation yet