An auto-tuned apparatus for a band-pass filter (30), wherein, the generated reference signals having a frequency to be set are mixed in a mixer (60) with the output of the band-pass filter (30). These reference signals are also input to the band-pass filter. The direct current component of the output signal of mixer (60) are filtered in a low pass filter (61) and via A/D converter applied to the controll circuit (50).
This control circuit (50) controls via a motor driver (32) the motor (33) for tuning the band pass filter (30) in such a way that the center frequencies of the band-pass filter (30) agrees with the frequency of the reference signal in accordance with the said direct current component. The center frequency of the band-pass filter (30) can thus be adjusted automatically to the desired set value using a simple circuit construction and with a better precision than in the conventional embodiment.