The circuit shown in the figure below is from the 1993 Linear Technology Applications. The operational ones used are uncommon and the use of equivalents can be analyzed.
We found this circuit in a technical documentation on the National Semiconductor LM3909. The...
This circuit was obtained from a 1986 Spanish magazine Resistor. The magazine no longer exists, but...
This circuit was found in old American documentation. The operational amplifiers are from the...