Q-enhancement of a low-power gm-C bandpass filter for closed-loop sensor readout applications

In this paper, a Q-enhancement technique for gm-C biquadratic bandpass filters is discussed. The frequencies of the parasitic pole-zero pair of a low-transconductance OTA are altered with an additional compensation capacitor, which cancels the nonidealities of the resonator. The presented technique is used to design a resonator which fulfills the requirements on a loop-filter for closed-loop delta-sigma sensor readout applications. The high stability of the Q-factor against transconductance and center frequency tuning, as well as against process variations is discussed and demonstrated with transistor-level simulations. The designed resonator exhibits a 3-sigma worst-case Q-factor larger than 3600 at the nominal center frequency of 25 kHz and a Q-factor larger than 1000 over the tuning range from 13 kHz to 32 kHz.