An electrical device comprises analog conversion circuitry having an input and an output. The electrical device is essentially provided for converting a first input signal within a first frequency range applied to the input to a first output signal within a second frequency range different from the first frequency range at the output. The electrical device further comprises a signal adding means for adding at least a portion of the first output signal as second input signal to the first input signal. The analog conversion circuitry is also capable of converting the second input signal, which is within the second frequency range, back to the first frequency range. Additionally, a characteristic deriving means is provided for deriving at least one characteristic of the electrical device from the frequency converted second input signal, which appears at the output of the analog conversion circuitry.