Operational, RF, and Current Amplifiers and Their Ubiquity
Daniel B. Talbot · 2020
Operational amplifiers, inverting and non-inverting mode and the reason the latter exhibits better signal-to-noise ratio (SNR), and operational transconductance amplifiers (OTAs) and class-C and F high-efficiency amplifiers are explained in this chapter. Reciprocal networks allow input and output terminals to be swapped without consequence to gain in an op-amp application, but with a possible consequence to noise. A short-cut is presented using the Miller equation to “back-of envelope” calculate closed-loop gain. The Miller effect is useful for capacitor neutralization. Description of the transistor as either a current conveyor (grounded base or gate) or as a transconductance amplifier (grounded emitter or source) is provided. High bias current for improving SNR is discussed, with concomitant discussion of shot and resistor noise. Gyrators synthesize inductors. A high-frequency amplifier circuit is used that is a two-transistor Darlington with feedback. The circuit is modeled and analyzed. The current conveyor is discussed and its advantage for both high gain-bandwidth (GBW) and high dynamic range. By handling signal currents rather than voltages, one largely escapes the Miller effect. SPICE calculations of the linearity of the open-loop nature of a current conveyor and closed-loop nature of an op-amp are comapared. Cascode circuits are not immune from the Miller effect in layout.