rfmems
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Description of the circuit
1, LDO+push pull VCO 2, LDO output biases VCO, inductor center tap feedbacks to LDO inputA, inputB is reference voltage 3, LDO: differential current mirror load amp.+miller compensated pmos
Objective
To simulate the LDO stability when the VCO is running in steady state.
Problem
The circuit is mulit-loop, LDO feedback, miller compensation. There is no way to cut all the loops at once. So I put the probe at LDO feedback path (from inductor center tap to LDO inputA). But I got strange results from simulation. Simulated gain drops to 0dB from DC to 100Hz, and then slowly increases to peak 40dB at 50KHz. Phase margin also started from 0 at DC and increases to 90 at 50KHz.
Comparing dc/tran+stb VS. pss/pstb, the simulation results are similar when freq>100KHz, but below that, pss+pstb makes no sense to me.
Question
1, I guess multi-loop circuit stability simulation is out of pstb's capbility, but did anyone have luck with that issue?
2, If it is not possible to simulate with pstb, is there a solution to this kind of stability simulation?
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