A 5.4-mW 50-MHz 29.3-dBm-IIP3 Fourth-Order Low-Pass Filter

This paper presents a continuous-time 4
^th
-order low-pass filter with 50MHz cut-off frequency. The proposed two-stage opamps in the filter use push-pull output stage to enhance the in-band linearity. High linearity of +29.3dBm IIP3 is achieved at 30MHz. Simple R-C compensation is adopted for high unity-gain-bandwidth of the opamp. The R-C compensation elements in the output stage is also served as the second integrator of the biquad for power reduction. The low noise characteristics of the passive integrator improve the noise performance of the filter. The in-band output integrated noise is -61.7dBm. The SNR for a -41dB-THD is 72.1dB. This filter draws only 3mA from 1.8V supply voltage. The filter prototype has been fabricated in 180nm CMOS process. The achieved high figure-of-merit of 164.8dB.J
^-1
validates the good power efficiency of the filter.