Found in Motorola documentation from the 90's, this circuit has a high input impedance. The power supply must be symmetrical. The circuit can be implemented with modern operational amplifiers.
This circuit was found in a 1960 transistor manual from Sylvania. It measures the intensity of...
I found this circuit in an old Argentine publication from 1973. The components are no longer...
Found in Ferranti's 1969 documentation, this circuit can be mounted with a modern equivalent...