How could I sim. VCO + Mixer + LNA in spectre ?

Discussion in 'Cadence' started by smartchi, Nov 2, 2003.

  1. smartchi

    smartchi Guest

    Dear all,

    I have a question about the spectre simulation method of the VCO + Mixer
    + LNA. I hope anyone could help me.

    Actually, I have successfully simulated the VCO and Mixer+LNA
    separatedly using the spectre. Which is using the special function, such as
    pss, pxf or pnoise etc, to simulated the phase noise, oscillating frequency
    in the VCO and 1dB compression point, iip3 or power gain in the Mixer+LNA.

    However, how could I simulate the overall circuit, VCO+Mixer+LNA, to get
    the simulation result such as 1dB compression point, iip3, noise figure

    Best Regards,

    smartchi, Nov 2, 2003
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  2. You're going to have difficulty simulating the VCO+Mixer+LNA with a large signal
    input to the LNA. That's because whilst PSS can run in both driven and
    non-driven (i.e. oscillator) modes, in both cases it needs to simulate over 1 period
    of the beat frequency of all the frequencies. With a driven input, and a free-running
    oscillator, the beat frequency is chaotic - a small change in the oscillator frequency
    can mean a huge change in the beat frequency - so you'd never get it to lock
    onto the PSS fundamental.

    You can simulate a small signal input to the LNA (because you then only have
    the oscillator frequency to contend with). However, that won't enable you to measure
    1dB compression point or IIP3 (but you could measure the noise figure).

    So, the best bet is to characterize the VCO, and then replace it with a
    behavioural model of an oscillator (for example, osc from rfLib). Then the
    circuit becomes driven, and you can then simulate it with either PSS or QPSS
    (depending on how the frequencies turn out).


    Andrew Beckett, Nov 8, 2003
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