Design of a 4-MHz analog integrated CMOStransconductance-C bandpass filter

A continuous-time eighth-order fully integrated CMOS transconductance-C bandpass filter is presented for operation at 4 MHz with 800 kHz bandwidth and 0.5 dB pass-band ripple. A phase-locked loop for frequency tuning and 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 1-dB passband attenuation, 75-dB stopband attenuation and S/N ratio, and 0.5% harmonic distortion for 0.5-V_p-p signal were observed. Offset of the transconductances was internally controlled by an offset-control loop to less than 4 mV. A temperature-insensitive transconductance design and the noise characteristics of the filter building blocks are also discussed