A 0.6mW 31MHz 4th-order low-pass filter with +29dBm IIP3 using self-coupled source follower based biquads in 0.18µm CMOS

Abstract

A highly compact low-pass filter (LPF) using self-coupled source follower based biquads is presented. The biquad cell synthesizes a 2nd-order low-pass transfer function in a single branch, using only two capacitors and a source follower with embedded local feedback for excellent linearity. A 4th-order Chebyshev LPF prototype is designed with a cascade of two biquads in 0.18μm CMOS, and occupies an active area of 0.1mm2. A cut-off frequency of 31MHz is measured with a stop-band rejection of 76dB. The prototype filter draws only 0.46mA current from a 1.35V supply, and achieves an in-band IIP3 of +29dBm. The averaged in-band input-referred noise is 22.8nV/√Hz, resulting in a dynamic range of 71dB.