This is the basic configuration of an operational amplifier sample & hold circuit. The FET and transistor are commonly used. The circuit is from an 80's documentation.
Details of the coil of this two-transistor generative receiver were not given. We found it in a...
This very high input impedance circuit is suggested by Texas Instruments. The circuit can be...
This circuit from an 80's publication also features low input capacitance. FET can be a modern...