BG9 - Classic Current Feedback Amplifier with DC servo

  • BG9 - first run

    BG9 - first run

  • PCB top view

    PCB top view

  • Schematic

    Schematic

  • FFT at 1kHz

    FFT at 1kHz

  • FFT at 5kHz

    FFT at 5kHz

  • FFT - IMD test

    FFT - IMD test

  • AC analysis

    AC analysis

I have to made a new revision of my very old project to correct few bugs and make some improvements. I decided to make this project with SMD components. Double die transistors (2x NPN, 2x PNP, NPN/PNP) are practically available only in SMD package. Small footprint, short PCB traces, very good thermal coupling, no VIA's inductance gives a lot of advantages over THT components. BG9 is a very classic and commonly used current feedback amplifier topology. In this design I have simplified VAS current mirror (one transistor removed) so the part of the current mirror forms LED biased cascode of the voltage stage. This gives a few components less and a bit higher output swing. The measurements confirm the strength of the CFA topology, simple, fast and furious. 

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