Folded Cascode Regen

A regenerative radio circuit using cascode and folded cascode stages.

The K596 FET is from a capacitor microphone that you can find in discarded phone headphones. It conducts about 300uA when the gate voltage is zero.  To use a more conventional FET you can try various LEDs connected between the source and ground to find a good negative bias voltage.

An increase in current through the FET causes:

More current to flow through Q3 and less through Q2.

A decrease in current through the FET causes:

Less current to flow through Q3 and more through Q2.

A change of input voltage to a FET or BJT transistor causes a non-linear change in current through the device. With an excess response to an increase in voltage compared to a decrease.  Q2 and Q3 separate those responses making the output from Q2 more suitable for smooth control of regeneration (controlled positive feedback to the tuning LC circuit.)

The collector output of Q3 goes to a current mirror AM detector circuit.

This circuit is experimental only.