Abstract: A system input is connected to a positive high voltage signal generator and a negative high voltage signal generator, the outputs of which are each connected to an output terminal via a photoconductor. The photoconductors are driven individually by an energizing circuit which has an input the sum of the system input and an attenuated signal fedback from the output terminal. For system inputs above a first predetermined level or below a second predetermined level, the appropriate photoconductor is rendered heavily conductive so that the output consists of the signal developed by the corresponding signal generator, which is proportional to the system input, less the small voltage drop which occurs across the photoconductor. For system inputs between the two predetermined levels, both high voltage signal generators deliver constant output signals and the energizing circuit reduces the conductivity of the appropriate photoconductor to produce the desired system output.

Abstract: A first operational amplifier feeds a DC signal to first and second inverter means which are operated in opposite senses of polarity and which convert the DC output signal of the first operational amplifier to first and second stepped-up differential AC voltages at the same predetermined synchronized frequency. These stepped-up voltages are then converted to corresponding first and second DC voltages. A second operational amplifier is connected to the output of the first operational amplifier which drives a LED-photoconductor circuit to provide further system gain.