A center- frequency measurement method for fine-tuning in an analog CMOS Gm/C filter

In this paper, a novel center frequency measurement method in an analog CMOS Gm/C band-pass filter is introduced. The purposed method is based on the measurement of stepresponse damping oscillation period which is related to over-shoot and under-shoot time difference of filter. This time difference is converted to a PWM (Pulse Width Modulated) control signal for filter automatic fine-tuning system. HSPICE simulation results in a 1MHz analog CMOS Gm/C band-pass filter are given. This new method has two advantages, First, it uses an easier to make, step test signal, instead of an exact single frequency sine test signal which is more difficult to make. Second, a simple and small analog hardware is used. It is more suitable for high-Q filters. The major drawback of our method is lower measurement accuracy in medium and low quality-factor filters.