High-frequency fully-tuned CMOS transconductance-C filter

The improved design and evaluation of a continuous-time eight-order fully integrated CMOS transconductance-C bandpass filter for operation at 4 MHz are presented. A PLL (phase-locked loop) for frequency-tuning and a four-point amplitude-locking loop for Q-factor-tuning at the reflection zeros of the filter are implemented. The transfer characteristics were found to be essentially within specifications: less than 75 dB stopband attenuation and S/N (signal-to-noise) ratio and 0.5% harmonic distortion for 0.5 V/sub pp/ signal were observed. Offset of the transconductances was internally controlled by an offset-control loop to less than 4 mV.<>