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Doing an AC analysis in a time-varying circuit.

Alli

Hi every one :-)

I wanted to do a simulation on an oscillator but I couldn't find any tools in cadence for that. Basically what I want to do is :

Considering an oscillator which is oscillating. During the oscillation I want to do a frequency domain transfer function (AC analysis). I need to linearize the circuit at several point in an oscillation period and find an AC transfer function at a single frequency from an input AC source to the output, and finally plot the magnitude of the transfer function in a period. Basically I want to simulate how the magnitude of a transfer function at a specific frequency is changed during the time (Oscillation period.) 
The frequency which I need the transfer the function is not important it could be exactly at the oscillation frequency or even a little off.
I read about PAC & PXF and if I'm right none of them gives me what I need.
I would appreciate it, if you have any idea.
Parents

  • Dear Shawn,

    Thanks for your response and sorry If my question was not clear enough. Let me make an example in order to clarify my motivation and what I want to do.

    For example I want to plot the impedance of one node of oscillator during one period and see how it's changing during one period of oscillation. Basically I need to know the instantaneous input impedance of a node of oscillation at a fixed frequency.

    To make it more clear, for a simple case I want to plot the gm of the transistor during the oscillation period. For this special case although I can use transient but for a general case which the node has some reactance, I couldn't find any solution. 

    BTW, I don't care about the phase of the impedance, what I want is only to know how the magnitude of an impedance is changing during a period.

    Also, I found a to simulation method, but It's a little tricky. I connect a DC source series to an inductor (which is like forcing the DC node voltages) to each node and define the DC value such that it's equal to it's transient counterpart and run the AC analysis, but the problem is that for each point I have to update the DC values, although It gives me what I want :-).

    If you have any other idea or can help me to make it automatic it would be a great help.

    Thanks,

    Ali

Reply

  • Dear Shawn,

    Thanks for your response and sorry If my question was not clear enough. Let me make an example in order to clarify my motivation and what I want to do.

    For example I want to plot the impedance of one node of oscillator during one period and see how it's changing during one period of oscillation. Basically I need to know the instantaneous input impedance of a node of oscillation at a fixed frequency.

    To make it more clear, for a simple case I want to plot the gm of the transistor during the oscillation period. For this special case although I can use transient but for a general case which the node has some reactance, I couldn't find any solution. 

    BTW, I don't care about the phase of the impedance, what I want is only to know how the magnitude of an impedance is changing during a period.

    Also, I found a to simulation method, but It's a little tricky. I connect a DC source series to an inductor (which is like forcing the DC node voltages) to each node and define the DC value such that it's equal to it's transient counterpart and run the AC analysis, but the problem is that for each point I have to update the DC values, although It gives me what I want :-).

    If you have any other idea or can help me to make it automatic it would be a great help.

    Thanks,

    Ali

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