An area efficient low noise 100 Hz low-pass filter

A technique based on scaling a filter's capacitor currents to improve the noise performance of low frequency continuous-time filters is presented. Two 100 Hz low-pass filters have been implemented: a traditional low pass filter (as reference), and a filter utilizing the above mentioned current scaling technique. The two filters utilize approximately the same silicon area. The scaled filter implements the scaling by use of a MOS based current conveyor type CCII. Measurements indicate that the current scaled filter results in a noise improvement of approximately 5.5 dB over the reference filter when a class A/B biasing scheme is used in the current divider. Obtaining identical noise performance from the reference filter would require a 3.6 times larger filter capacitor. This would increase the reference filter's die area by 100%. Therefore, the current scaling technique allows filters with improved noise performance/dynamic range, given a fixed silicon area and a fixed power supply.