Found in American documentation from the 1980s, this circuit has a diode feedback. At the exit we have an indicator LED. The LM3900 is a transconductance operational amplifier.
This receiver for infrared remote control was found in the Philips Databook of 1990, The circuit...
Found in an English publication from the 1980s, this circuit uses components that are still common...
This circuit was found in Maxim's documentation from the 90's. The frequency of the circuit is...