Method for automatic frequency adaptation of a filter in a closed loop

A signal processing device, comprising:

• a closed control loop with a first filter having a resonant frequency and a delta sigma modulator;
• and
• a frequency adaptation circuit receiving an output signal of the delta sigma modulator, determining a first noise spectrum of the output signal of the delta sigma modulator in a first frequency band and a second noise spectrum of the output signal of the delta sigma modulator in a second frequency band, the first frequency band and the second frequency band being arranged symmetrically with respect to a given frequency, comparing the first noise spectrum in the first frequency band with the second noise spectrum in the second frequency band, generating an adaptation signal that causes a frequency adaptation of the resonant frequency if the first noise spectrum differs from the second noise spectrum, and outputting the adaptation signal to a control input of the first filter for adapting the resonant frequency to the given frequency in response to the comparison result.

A circuit arrangement for reading a capacitive rotation rate sensor, comprising:

• a signal processing device including a closed control loop with a first filter having a resonant frequency and a delta sigma modulator, and a frequency adaptation circuit receiving an output signal of the delta sigma modulator, the frequency adaptation circuit determining a first noise spectrum of the output signal of the delta sigma modulator in a first frequency band and a second noise spectrum of the output signal of the delta sigma modulator in a second frequency band, the first frequency band and the second frequency band being arranged symmetrically with respect to a given frequency, comparing the first noise spectrum in the first frequency band with the second noise spectrum in the second frequency band, generating an adaptation signal that causes a frequency adaptation of the resonant frequency if the first noise spectrum differs from the second noise spectrum, and outputting the adaptation signal to a control input of the first filter for adapting the resonant frequency to the given frequency in response to the comparison result;
• and
• a control unit configured to calculate and output a rotation rate signal based on the output signal of the delta sigma modulator.