It serves as a reference, since today we can have simpler and more compact solutions. This circuit is from an Electronics Experimenter Handbook from 1992. The integrated circuits are from that time.
This 3 and-a-half digit circuit was found in a Teledyne documentation from the 90s. The circuit uses...
We found this circuit in an English publication in 1976. The circuit is based on the use of a...
This filter of two transistors has the cutoff frequency determined by the formulas next to the...