A low-distortion BiCMOS 7th-order Bessel filter operating at 2.5 V supply

This paper presents the design of a 7th-order continuous-time Bessel filter using a new low-voltage and highly-linear BiCMOS OTA. A high-gain and parasitic-insensitive integrator is obtained by using an active capacitor scheme. The filter has been fabricated in a 1 /spl mu/m, double-poly 6-GHz BiCMOS process. The filter is operated at 2.5 V supply and has a nominal -3 dB cut-off frequency set at 600 kHz. The inband group delay variation is less than 10 ns. The THD measured with a 100 kHz input signal is less than -49 dB for a 2 V/sub pp/ amplitude. The filter can be frequency tuned with an external resistor over almost a decade with a gain variation less than 0.2 dB. The dynamic range is about 77 dB. A CMRR of 53 dB in the passband is observed, thanks to a careful common-mode control strategy.