We found this circuit in the Linear Applications Hanbook of the National Semiconductor in 1994. The semiconductors used are not very common today.
This TTL circuit for digital signals up to a few dozen megahertz was found in old documentation, but...
This circuit with an operational amplifier was found in the magazine Radio Electronics of...
This detector is from the 1990 Motorola Dataar Databook, but can be adapted to work with more...