Audio Electronics - Cascodes, Folded Cascodes, and Current Mirrors (Part 3)

For those readers following the fascinating article series by Morty Tarr on "Cascodes, Folded Cascodes, and Current Mirrors," this final article in the series contains an additional section with important aspects of amplifier design. In the first two parts of this article series, Tarr discussed the technical merits of cascodes and related circuits. This useful addendum covers a simple test circuit for matching FET devices, the fascinating story of the Blowtorch Line Stage design, and additional notes on inverting and non-inverting amplifier stages and integrators. This article was originally published in audioXpress, December 2021.

In Part 1 of this three-part article about circuit topologies that are used to provide specific functions for an amplifier design, the author discussed cascodes and folded cascodes. In this Part 2, he focuses on current mirrors and line stages. As the author writes, “As designers, we have many devices to choose from. Some devices are ideally suited to certain tasks. Other tasks require performance that is difficult to achieve. While many excellent devices exist today, ideal devices do not exist, except maybe in Spice simulations.” This article was originally published in audioXpress, October 2021.

For this audio electronics article, Morty Tarr wrote a fascinating exploration of circuit topologies that are used to provide specific functions for an amplifier design. Cascodes, folded cascodes, and current mirrors are some of these topologies, intended to improve the performance of the devices, but which also add complications. In the first of a three-part series, the author discusses cascodes and folded cascodes, useful to improve high-frequency response and device linearity.