Patent ID: 6944569

Claim:
An apparatus for generating an electronic test signal, comprising a user input control, a processor, a digital-to-analog output stage, a test signal output, a feedback input, and an analog-to-digital feedback input stage, wherein: a) the user input control is operable to allow a user to select the frequency domain characteristics of a desired electronic test signal including a user-defined set of amplitudes and phases of a fundamental frequency and one or more harmonic frequencies; b) the processor is arranged to receive from the user input control said user-defined set of amplitudes and phases and to generate from the user-defined set of amplitudes and phases an output set of amplitudes and phases for the fundamental frequency and one or more harmonic frequencies; c) the processor is arranged to convert the output set of amplitudes and phases into a first time domain set of amplitudes extending over at least one cycle of the fundamental frequency; d) the digital-to-analog output stage is arranged to receive from the processor the first time domain set of amplitudes and to generate therefrom an electronic test signal corresponding to the time domain set of amplitudes and to present said electronic test signal to the test signal output; e) the feedback signal input is operable to allow a user to feed back the electronic test signal into the analog-to-digital feedback input stage and to generate therefrom a feedback time domain set of amplitudes extending over at least one cycle of the fundamental frequency; f) the processor is arranged to receive the feedback time domain set of amplitudes and to generate from the feedback time domain set of amplitudes a feedback frequency domain set of amplitudes and phases for the fundamental frequency and one or more harmonic frequencies; and g) the processor is arranged to compare the feedback frequency domain set of amplitudes and phases with the user-defined set of amplitudes and phases, and when necessary to modify the output set of amplitudes and phases depending on said comparison in order to reduce any differences between the feedback frequency domain set of amplitudes and phases and the user-defined set of amplitudes and phases.