The electrical test circuit (5) comprises a first input (51) for receiving a test signal of an integrated circuit (4), a second input (52) for receiving a control signal and a third input (53) for receiving a normalized reference signal, particularly one that is formed to be synchronous with the test signal. Using a control device (55) of the electrical test circuit (5), the deviation and/or the amplitude and/or the phase of the reference signal and/or of the test signal can be varied. A measuring device (56) generates, by subtracting the reference signal from the test signal, a difference signal which is output via an output (54).