A 77-dB-DR 0.65-mW 20-MHz 5th-Order Coupled Source Followers Based Low-Pass Filter

A compact coupled source followers (CSFs)-based low-pass filter (LPF) topology is presented with excellent power efficiency and high linearity. It synthesizes a 3 ^rd -order low-pass transfer function in a single stage that is comprised of two CSFs and three capacitors. It can also be configured to a 2 ^nd -order by disconnecting a capacitor. A 5 ^th -order LPF prototype is designed with a cascade of two proposed filter stages in a 0.18- $\mu \text {m}$ CMOS process. Operating under a 1.3-V supply voltage, the filter consumes 0.5-mA total current and achieves a −3 dB bandwidth of 20 MHz. A total harmonic distortion (THD) of −39.5 dBc at the output is measured with a +6.6 dBm (i.e., 1.35 $V_{{\text {pk}-\text {pk}}}$ ) 2-MHz input signal. The measured in-band 3 ^rd -order input interception point (IIP3) is +24.5 dBm. The resulting dynamic range (DR) at −40 dBc THD is 76.9 dB, with 15.3-nV $\surd $ Hz averaged in-band input-referred noise. The chip occupies an active area of 0.12 mm ² .