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Question in Amplifier Presicion Lab ： Low THD+N Design

Wesley Huang
Expert 1030 points

Other Parts Discussed in Thread: BUF634A

HI Team,

 

According to the video in LOW THD+N 3: “composite amplifiers can be a great way to decrease output stage distortion. When you place a buffer in the feedback loop of another amplifier, this increases the amount of loop gain around the output stage”

 I want to know more specific information about the composite amplifier design as the video said. Do you have any reference design about this?

 

Best regards

Zhihong Huangs

  • 0
    Guru 48395 points

    Well that comment is actually a mistake - Using a buffer like the BUF634A does not add gain in the loop. It does often provide a higher output current, possibly more linear output stage - however, it also adds inside the loop delay which has to be accounted for in phase margin - 

    If you actually added an amplifier inside the loop, then yes the LoopGain is increased with the same phase margin concerns - one way to think about that is you have replaced the original output stage with maybe a higher power one operating at gain - the original amplifier has to work less possibly improving the HD performance kind of like creating a decompensated overall design from perhaps a unity gain stable front lend stage. 

  • 0 in reply to Michael Steffes
    Expert 1030 points

    HI Michael,

     

    Get this.

    Thanks for your reply.

    Best regards

    Zhihong Huangs