MOSFET-C filter, with low excess noise and accurate automatic tuning

Continuous-time integrated filters having a maximum dynamic range at the audio-frequency range are obtained using MOSFET-C filters. Using MOSFET-C filters in combination with a well-designed BiCMOS amplifier, the detrimental influence of 1/f noise can practically be eliminated and the filter noise is completely determined by the unavoidable thermal noise of the filter resistors. A 98-dB dynamic range (total harmonic distortion<0.3%) is obtained in a fifth-order Butterworth low-pass filter, while the overall 1/f noise corner frequency is limited to 250 Hz. Automatic adjustment of the filter cutoff frequency is performed using a novel all-silicon automatic tuning system that, compared with traditional automatic tuning systems, has reduced overhead circuitry