This circuit is from a 1968 documentation using one of the first integrated circuits available at the time, the TAA370. The circuit is powered by 1.3 V using a 200 ohm handset.
Medium and high power partially burned can be used as diodes in a simple Power supply as shown in...
This 80's Exar circuit has a carrier detector for frequencies up to 500 kHz. The circuit uses a...
This is a circuit suggested by Linear Technology in a 1980s documentation. The integrated circuit is from...