This circuit was found in ancient American documentation. Equivalent operational amplifiers can be used. The power supply must be symmetrical. The circuit provides an average output.
The figure below shows an AC transconductance amplifier with the National Semiconductor LM3900. The...
This common circuit using operational amplifiers was found in the 1993 issue of Radio Electronics Special...
This circuit provides a voltage at the output only when the input voltage exceeds a value that...