Docent lecture Gregor Lasser, Microwave Electronics Laboratory

Abstract: 

The most basic amplification circuit that we use since the advent of electronics – the common emitter, common source, or common cathode amplifier – is fundamentally limited in amplification due to an internal coupling capacitance that can be found in any practical device, independent of its technology. This drain to gate capacitance (for field effect transistors) acts as a negative feedback path, generally reduces the voltage gain of an amplifier, but can also lead to circuit instability and oscillation. This talk will discuss the negative effects of this capacitance, and explain different approaches how external circuitry can be used to cancel this capacitance – effectively neutralizing it. The talk will also outline how neutralization became popular in vacuum tube circuits, was re-developed for CMOS ICs and was recently applied to GaN devices, increasing the gain of microwave amplifiers.