We found this circuit in an old publication. The components used are rare today. Accuracy depends on the resistors in the input selection network. The circuit operates from 10 to 500 kHz.
This circuit with the 741 operational amplifier was found in the March 1995 issue of Electronics Now...
This circuit was found in a General Electric documentation from 1966. It uses discrete components...
We found this circuit in a French technical documentation from 1982. The circuit can be...