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Regarding SP simulation for phase shifter (phase interpolator)

Jay815
Dear all,

I would like to ask a question about S-Parameter (SP) simulation for phase shifter (phase interpolator) design. I am designing a 10GHz phase shifter using I/Q interpolation (so called, Cartesian phase shifter or phase rotator). In order to see the phase shift, I ran a transient simulation and it worked as expected.

However, when I ran a SP simulation, here is some simulation information,

  1. There are two phase shifters: One’s output is reference and the other’s output is phase shifted.
  2. The input port (port#1) generates an I signal, and the output ports (port#2 and port#3) are connected to output LC loads of two phase shifters. (Of course, I have one more input port for Q signal generation)
  3. In order to see the phase difference of two phase shifter outputs, I checked the phases of S21 and S31. However, the phase difference between S21 and S31 is almost zero, which is not what I expected.

Hence, I am wondering if I cannot see the phase difference of the phase interpolation circuit with SP simulation or not. If it is possible, I am wondering what I did wrong.

For your information, when I designed a LC passive phase shifter, a SP simulation in the same manner worked fine.

Could you please advise?

Thank you so much!

Regards,

Jay
  • I would like to add one more thing. When I ran an AC simulation, the output phase difference of the two phase shifters was what I expected. So I might conclude AC and transient simulation work. However, I am still wondering why SP simulation does not work. Could anyone give an advice? Thank you!

    -Jay

  • Jay,

    I don't think there's any way to specify a phase shift on a port for s-parameter analysis. The only parameters on the port you have to control the phase are the phase parameter (which along with the mag parameter specify the size of the AC input - this is only used for ac analysis - there's also pacphase which is used in the pac, hbac and qpac analyses), and the sinephase parameter which is only used in time-varying analyses (e.g. tran).

    So that's why it doesn't work - it's not a bug, but since you're not injecting a signal in sp analysis, I'm not sure it really makes sense.

    Regards,

    Andrew.

  • Hi Andrew,

    I greatly appreciate your comment!

    Based on your comment, I may understand the reason and would like to make sure with you. In order to apply Q-phase signal, I set “Port properties > Source type: sine, Phase for Sinusoid 1:90”. But this 90deg signal is only for transient analysis not for SP analysis. Am I correct?

    Actually, I ran this simulation to make sure my future measurement setup. I will test the phase shifter with a vector network analyzer (VNA), i.e. phase difference between two S21 (one is input-to-phase shifter output, the other is input-to-reference). Since I/Q signals are internally generated on a chip, I think this measurement is feasible with a VNA. I would also like to ask your opinion about this measurement plan. Could you please advise?

    Thank you so much for your help!

    Regards,

    Jay

  • Jay,

    For the first question, the "phase for Sinusoid" is only relevant when you are generating a sinusoid - so in large signal analyses such as tran. For sp analysis you are not generating a large signal sine wave, so this is not used.

    For the second question I am not the right person to ask - it's been a long time since I was last testing designs on the bench (18 years?) - apart from the odd hobby thing at home, and even then not sure I ever used a VNA.

    Regards,

    Andrew.

  • Andrew,

     

    Thank you very much for your help and quick answer! Now I came to know more about Spectre SP simulation. :)

     

    Regards,

    Jay

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