On the -3 dB Bandwidth of a 3-Pole Feedback Amplifier
Venkatnarayan Hariharan · 2024
Analysis of key metrics of higher-order feedback amplifiers is usually done using circuit simulations. It is well known that this activity doesn't lend itself well for hand-analysis, due to the intractable nature of the problem. In this paper, we scope down the problem to special cases of 3-pole systems and focus on one metric, viz. the -3 dB bandwidth. We present a closed-form analytical model for the bandwidth of a 3-pole feedback amplifier and identify the key governing ratios, and it's limits of accuracy are also discussed. The derivation of the model is presented, and it is validated versus a numerical solution by showing plots at several values of key governing parameters. It is also shown how this model is a large improvement over the first-order rule of GBWP (Gain Bandwidth Product) being constant, which in reality is applicable only to single-pole systems.