BG9 - Classic Current Feedback Amplifier with DC servo
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.