Do you want to introduce other methods to achieve a voltage controlled resistance, so that i can check them out?

PWM, by switching the ground end of a resistor at an ultrasonic frequency and low-pass filtering the result?
I haven't seen this method used in published circuits and I haven't tried this in the real world, but simulation looks promising -


Edit:
The three waveforms are for respective different PWM pulse widths.

 

 

The traditional circuit for creating a DAC (Digital to Analog Converter) was to create an R-2R ladder of resitrors to convert a digital value into an analog value by means of controlling the total resistance of the ladder. I should point out this technique works best on a silicon die, and is less likely to be used with discrete parts. I is however possible to construct.

 

thanks a loteverybody.
I will check them out next!