This circuit was found in Texas Instruments documentation from 1968. The transistors are from that time, admitting modern equivalents. The response ranges is from 20 to 20 000 Hz.
This circuit was found in Radio Electronics magazine from the 90's. The circuit is for small NiCad...
The XR2206 is not a common component today, but if you have one you can build this function...
This circuit is a four-quadrant multiplier using an LM3900. The circuit was found in the July 1988...