Apparatus for measuring a signal voltage including a current source with a control input on which said signal appears

An apparatus for measuring the voltage of a signal which is substantially sinusoidal comprising a source of operating voltage having first and second output terminals, first and second transistors each having emitter, collector and base terminals, a first resistor connecting the emitter terminal of said first transistor to the first output terminal of said source, the base terminal of said first transistor being adapted to receive signals to be measured, means for connecting the collector terminal of said second transistor directly to the second output terminal of said source, a second resistor connecting the collector terminal of said first transistor to the emitter terminal of said second transistor, a capacitor connecting the collector terminal of said first transistor to the base terminal of said second transistor, a current indicating means having one terminal connected to one of the output terminals of said source and having another terminal, phase inversion means having an input connected to the base of the second transistor and an output connected to the another terminal of said current indicating means, first unidirectional current conducting means having one terminal connected to the another terminal of said current indicating means and having a second terminal, and nonreactive means for directly connecting the second terminal of said first unidirectional current conducting means to the base terminal of said second transistor.