The figure shows how to use an operational circuit as a voltage divider. The circuit is from a Radio Electronics magazine from June 1986. The reference voltage is given by a zener diode.
This circuit was obtained from an American 80's documentation. The balanced mixer can be shown in...
This circuit was found in a 90s Electronic Engineering. The quadruple operational amplifier can be...
I found this circuit in an English publication from 1989. This configuration can be mounted with...