Can Simulink's behavioral RFModelPLL simulate phase noise variations caused by different output loads?

For a school project i want to simulate the phase noise of a oscillator and what happens to the phase noise when the oscillater has two unknown loads.

I have done simulations in simulink using the RFModelPLL. I also moddified this model so the PLL output has two 50 ohm loads conected. i also edited the load impedance to 25 ohm and 100 ohm. this didn't do anthing with the results.

Is it posible to simulate the impact that different loads have on the phase noise of the clock?

Is the RFModelPLL aa good choise to use to simulate this or is there a another moddel that i can use to simulate this?

thanks in advance

Answer 1

[Ritam]

What you’re observing is generally consistent with how many behavioural or system‑level PLL models operate. In such models, the phase noise behaviour is mainly governed by the reference source, loop dynamics, and the VCO noise profile, so changes in the external load may not directly reflect in the phase‑noise results.

That said, in practical implementations, load variations can influence phase noise indirectly through mechanisms such as:

1. Load pulling, where changes in load impedance slightly alter the effective resonator or tank loading and may result in small frequency or phase modulation.
2. AM‑to‑PM conversion, in which load‑dependent amplitude variations interact with nonlinearities and appear as phase noise.
3. Supply pushing or bias modulation, where changes in output loading affect current draw, which can couple into the VCO through supply or bias paths.
4. Output buffering, which is often intentionally used in real oscillators to reduce sensitivity to load variations and may mask these effects if modelled ideally.

If your goal is to explore these effects at a conceptual level, one possible workflow could be to introduce a simple load‑sensitivity mechanism into the existing model to represent weak load pulling or AM‑to‑PM coupling, rather than relying on ideal source behaviour. Another complementary approach might be to use the phase‑domain PLL modelling and phase‑noise measurement capabilities in Mixed‑Signal Blockset, which are well suited for studying how different noise sources are shaped by PLL dynamics.