SYclotron input stage

This is a circuit I came up with some years ago, based on the cross-coupled inverter; although at first glance, many people thing “cascode,” it isn’t. Note that the FETs are p-channel and configured as source followers. Each FET drives the cathode of one side and the grid of the other. Its great virtue is a low input capacitance, which I leveraged in the Equal Opportunity phono preamp design, published in Jan Didden’s excellent Linear Audio bookzine. Note that the figure he used in the blurb is NOT actually the EO topology!

Besides low input capacitance, it also has excellent common-mode and power supply rejection. This is an early version- I’ve made some improvements which greatly increase linearity and swing. I’m currently doing a more complete write-up on this circuit as a power amp input stage for AudioXpress.