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I am working on the design of a RF power amplifier. I want to use a feedback from the drain to gate. How can I determine the type of feedback (positive,negative) used. I am using a series RC feedback ? I am designing my circuit in cadence. If I use s-parameter simulation, which s parameter should I observe on the Smith Chart ?

Thank you, Yash

Yash
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  • What you will want to do is to make a power divider to direct part of your PA output in a feedback loop, if you want to drive the RF Output power Level. I think you will have to drive the Voltage level of your PA in regards of the target power output. On a personal note: Have you made the RF PA impedance matching? I'm designing my own PA and I'm stuck to the impedance matching. – Wireless Learning Feb 04 '22 at 10:19
  • Hi Lucas, thanks for the help. Yes I have worked on impedance matching. Actually this is my first project on IC design but will be happy to help you however I can. – Yash Feb 05 '22 at 11:57
  • Hi, I have opened a question, could you please have a look and tell me If you have encountered such problems. I'm trying to make the impedance matching using S-Parameters. I searched online for reference and guidelines but find none that help me with my problems. The question : https://electronics.stackexchange.com/questions/606139/s-parameters-power-amplifier-impedance-matching – Wireless Learning Feb 07 '22 at 08:54

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Could you please add :

  • Amplifier reference
  • Frequencies of operation
  • Required output power level

If you want to observe the gain part of your amplifier you want to look at the S21. If you are not familiar with S-Parameters, they are read like this : Sxy is the power level + phase of an excitation injected at y observed at x. In this case you inject something at the port 1 and you have (hopefully) more at the port 2.

You should look at power divider, depending on your frequency of operation it can be made with discrete components or with copper traces directly on your PCBs. The idea is to take a small part of your output, rectify it to have a DC voltage proportional to your output power. Then make a feedback loop to your DC power supply.

Good luck !

Wireless Learning
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    Many thanks for your response. I looked at your question through the link you posted above. I am still a rookie in IC design and it is beyond my scope as your circuit is way too advanced. Also, I am working alone and do not have experienced colleagues to help you out. I am sorry. Wishing you good luck with your project. – Yash Feb 08 '22 at 03:07
  • No problem, don't hesitate if I can be of any help to you I will be glad to help you. – Wireless Learning Feb 08 '22 at 07:43