Derivative-free active-RC elliptic filter using cascade of biquads in 28 nm CMOS

A highly linear, 3rd order, active-RC low-pass elliptic filter with Variable Gain Amplifier (VGA) is presented. The new derivative-free biquad topology for an elliptic filter could be easily extended to a higher order filter using a cascade of biquads and it will have a zero capacitive spread when used along with a VGA. It is introduced to minimize the power consumption of an active-RC filter in a radio receiver. The combination of a filter+VGA provides a ripple of just 0.4 dB through 35 MHz pass-band and sharply attenuates out of band carriers by placing a zero at 50 MHz. A Filter+VGA together achieves an IIP3 of 29.91 dBm and integrated input referred noise of 44.96 μVrms consuming 54 mW. The proposed architecture is simulated using 28 nm CMOS technology and verified through extensive spectre simulations.