This circuit simulates a resistor controlled by digital signals. We found it in American documentation from the 90s. The basic component is a CMOS 4016 or 4066 digital switch.
The gain of the operational amplifier shown in the figure depends on the feedback resistor,...
This circuit is from a 1970 publication. The time constant is given by 1.3R x C where R is the...
This commercial medium and short-wave radio was manufactured in Japan in the 60s. The circuit has...