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.
In the figure we have a typical polarization circuit for MOSFETs with a high impedance...
Found ina 1970 American documentation this fast-reading circuit uses a photodiode. Transistors...
Found in a 1970's Radio Electronics, this circuit uses a triac to switch loads on the AC network. This...