A 77-dB-DR 0.65-mW 20-MHz 5th-Order Coupled Source Followers Based Low-Pass Filter
Yang Xu, Hang Hu, Jason Muhlestein, Un-Ku Moon
Abstract
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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order by disconnecting a capacitor. A 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -order LPF prototype is designed with a cascade of two proposed filter stages in a 0.18-μm 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pk-pk</sub> ) 2-MHz input signal. The measured in-band 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -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√Hz averaged in-band input-referred noise. The chip occupies an active area of 0.12 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .