This circuit is from 1994 documentation by National Semiconductor. What it does is convert the square root of a voltage to a proportional frequency.
This interference rejection circuit for telegraphy was found in a 1980s documentation for radio...
This circuit was found in a 90s Popular Electronics. Both the coupler and the MOSFET can be of any...
This is a traditional oscillator configuration with an operational amplifier using a symmetrical power...