Why was the continuous-time VCO block discontinued in the Communications Toolbox, and what is the recommended way to model it for PLL/RF synthesizer design?

I am designing a PLL/frequency synthesizer for an RF transceiver, and for this application I require a continuous-time VCO to generate clean I/Q signals at the desired frequency through the PLL.

Previously, the Communications Toolbox included a continuous-time VCO block, but in recent releases it only provides square-wave VCOs. The Mixed-Signal Blockset has similar square-wave oscillators, which are not ideal for my RF modeling needs.

My questions are:

1. What is the recommended approach to realistically model a continuous-time VCO in Simulink for PLL and synthesizer applications?
2. If I use an analog filter after the square-wave VCO to approximate a sinusoid, will this introduce additional noise or artifacts?
3. If I design my own continuous-time VCO using a MATLAB Function block, is there a straightforward way to add phase noise (similar to the existing VCO block functionality), or do I need to manually implement mean/variance-based noise processes each time?

Any guidance, examples, or suggestions on how to best model a clean continuous-time VCO with realistic phase noise in current MATLAB/Simulink would be greatly appreciated.

Answer 1

[dpb]

I "know nuthink!" about the field, but the release notes for R2024a contain the following

VCO and PLL blocks have been removed

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These VCO and PLL blocks have been removed:

• Phase-Locked Loop (R2024a)
• Baseband PLL (R2024a)
• Charge Pump PLL (R2024a)
• Linearized Baseband PLL (R2024a)
• Continuous-Time VCO (R2024a)

To design voltage-controlled oscillators (VCOs) and phase-locked loops (PLLs), use the Phase-Locked Loops (R2024a) (Mixed-Signal Blockset) blocks.

[Humayun]

Thanks for your response. Yes, these blocks are removed by MATLAB but inorder to realistically model the frequency synthesizer i need to model a continous-time VCO but not sure where to add the phase noise from. By the way appreciate your response.

[dpb]

Sorry can't be of more help but I know nothing in the area to be able to infer how to use the replacement blocksets; looking at the documentation wasn't of help to me in seeing how to use the new toolset.

Do you have a model using the previous components? If so, my recommendation is to submit a support request to official Mathworks support requesting guidance in moving that model to the new toolbox.

Submit to Mathworks at <Product Support Page>