Semiconductor Devices: JFET Cascode Amplifier

A JFET cascode amplifier is a combination of a common source stage feeding a common gate stage. It is configured using a single drain current bias path for both devices, thus the circuit is not much larger than an ordinary common source amplifier. The cascode arrangement reduces the impact of the Miller effect, and tends to produce a higher upper break frequency than a simple common source stage.

Please note, there is a small error at 22:50 due to sloppy cut-and-paste on my part. The output network equation shows the capacitance as Cgd Millerized. This is not true. The actual value is just Cgd because it's a common gate configuration. In this case the difference is a matter of just a few tenths of a picofarad and it does not impact the accuracy of the overall result. Sorry about that, chief.

References: Semiconductor Devices: Theory and Application/2E; Chapter 17, section 3.

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