a programmable , low - current voltage source for small - signal electronic equipment , such as portable cellular telephones , is achievable by generating and applying a bias voltage and a reference voltage across a voltage divider circuit . consequently , a low - current output voltage is generated at the center junction of the voltage divider circuit . adjustment of the low - current output voltage level is accomplished by adjusting either the bias voltage level and / or the reference voltage level . the adjustment of the bias voltage level and / or the reference voltage level , in turn , is controlled by a programmable , microprocessor - based waveform generator .