Low order filter circuit having frequency correction function, frequency correction method for the low order filter circuit, and high order filter circuit

A low order filter circuit having a frequency correction function, including:

• a second order filter unit for receiving an inputted signal and filtering the inputted signal to retrieve a predetermined band signal and output the predetermined band signal;
• an analog-to-digital converter (ADC) having a first working status and a second working status, for detecting a peak of the predetermined band signal from the second order filter unit and digitalizing the peak when the ADC is in the first working status, and for detecting and converting the predetermined band signal from the second order filter unit to a digital signal and outputting the digital signal when the ADC is in the second working status;
• and
• a digital correction unit for comparing the digitalized peak with a default value and generating a comparison result, and according to the comparison result, the digital correction unit generating a frequency control signal and a working status control signal and sending them as feedbacks respectively to the second order filter unit for adjusting its working frequency and to the ADC for switching its working status, wherein the digital correction unit includes:
• a register unit for storing the digitalized peak;
• a comparison unit for comparing the digitalized peak with the default value and generating a comparison result;
• a control unit for generating the working status control signal and a counting mode control signal according to the comparison result from the comparison unit;
• and
• a counting unit for performing forward or backward counting according to the counting mode control signal from the control unit to generate the frequency control signal.