This circuit was found in Siliconix documentation from the 1980s. Equivalent operational amplifiers can be used and the output current is very low.
This configuration of the 1980s uses NAND A-type CMOS ports, which have a linear response with...
The LEDs act as diodes, so if good they will show the same characteristic curve. Arrangment shown...
I found this circuit in an English magazine from July 1982. The circuit is still viable by using...