Stats

  • Locked Locked
  • Replies 2
  • Subscribers 126
  • Views 14828
  • Members are here 0
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

RX-Chain Noise Figure calculation with QPSS

Juanelin

Hi all,


I am currently simulating a receiver chain consistent of an LNA-Balun-Mixer combination using QPSS and QPNOISE as engines. My input port drives the LNA with a 50 Ohm impedance, while the output port serves as 100-Ohm load impedance to the mixer. So far, the gain of the complete Chain seems to correspond to the expectations (GAIN1+GAIN2+GAIN3) but the noise figure happens to be between around 3 dB higher than expected if I plug the single component gain/noise values into the Friis NF equation. I plot the NF using the "Noise Figure" option (SSB) under the QPNOISE results.

I was wondering if this 3 dB difference comes from the 100 Ohm output /50 Ohm input factor due to the single ended to differential conversion? So far I haven't found how the QPNOISE engine calculates the noise figure, but that would be my first guess. The receiver's building blocks are matched among them, 50 Ohm single ended, 100 Ohm for the differential ones, so I would discard at first instance any increase in the noise figure due to mismatch between components.


Any document or explanation would be greatly appreciated.


Thanks a lot,

Erick

Parents
  • Tawna
    Hi Erick,

    1. You didn't mention what version of IC software and what version of Spectre you are using.
    virtuoso -W
    spectre -W
    will give this information. If possible, use IC6.1.7 (latest ISR) and MMSIM 15.1 (latest ISR) from http://downloads.cadence.com .

    2. You mentioned that you are using qpss/qpnoise. Harmonic balance or Shooting Newton? Is the circuit strongly nonlinear (think square waves or more nonlinear)? Then use Shooting Newton. Otherwise use HB/HBnoise.

    3. It's difficult to say without seeing your design. I recommend contacting Cadence Support (http://support.cadence.com) to get help from the Application Engineer on Call.

    4. The Spectre and APS RF User Guide will give a lot of good information on how noise is calculated. I strongly recommend reviewing the noise chapter(s). There are several ways to access it:
    - type 'cdnshelp &' in your xterm
    - go to http://support.cadence.com and search for the Spectre and APS RF User Guide
    - In the hierarchy at <path_to_MMSIM>/lnx86/doc/spectreRF/spectreRF.pdf

    In Appendix A of the Spectreand APS RF User Guide, if I recall correctly, there is an example of a differential mixer that may help you with setup.

    best regards,
    Tawna
Reply
  • Tawna
    Hi Erick,

    1. You didn't mention what version of IC software and what version of Spectre you are using.
    virtuoso -W
    spectre -W
    will give this information. If possible, use IC6.1.7 (latest ISR) and MMSIM 15.1 (latest ISR) from http://downloads.cadence.com .

    2. You mentioned that you are using qpss/qpnoise. Harmonic balance or Shooting Newton? Is the circuit strongly nonlinear (think square waves or more nonlinear)? Then use Shooting Newton. Otherwise use HB/HBnoise.

    3. It's difficult to say without seeing your design. I recommend contacting Cadence Support (http://support.cadence.com) to get help from the Application Engineer on Call.

    4. The Spectre and APS RF User Guide will give a lot of good information on how noise is calculated. I strongly recommend reviewing the noise chapter(s). There are several ways to access it:
    - type 'cdnshelp &' in your xterm
    - go to http://support.cadence.com and search for the Spectre and APS RF User Guide
    - In the hierarchy at <path_to_MMSIM>/lnx86/doc/spectreRF/spectreRF.pdf

    In Appendix A of the Spectreand APS RF User Guide, if I recall correctly, there is an example of a differential mixer that may help you with setup.

    best regards,
    Tawna
Children
No Data

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.