Tone signal detection circuit for detecting tone signals

Tone signal detection circuit for a receiving circuit for detecting at least one tone signal of predetermined tone signal frequency (fE) which is contained in a received analog input signal, comprising a reference signal generator (41) for generating an analog converter reference signal which consists of a reference DC (VrefDC) and a periodic reference AC (VrefAC) having a variable fundamental frequency (fG), which is superimposed on the reference DC, an analog/digital converter (11) for converting the analog input signal into a digital data stream in dependence on the analog converter reference signal (Vref); and comprising a digital control circuit (20) which adjusts the variable fundamental frequency (fG) of the reference signal (Vref) generated by the reference signal generator (42) in accordance with the predetermined tone signal frequencies (fG) of the tone signals to be detected and evaluates the digital data stream output by the digital analog/digital converter (11) for detecting a data pattern corresponding to the tone signal.