A Third-Order Quasi-Elliptic N-Path Filter With Enhanced Linearity Through Clock Boosting
Aravind Nagulu, Yi Zhuang, Mingyu Yuan, Sasank Garikapati, Harish Krishnaswamy
Abstract
N-path filters show promise to realize tunable, high-quality on-chip filters. However, N-path filters remain restricted to sub-2 GHz operation, low frequency selectivity, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\approx }0$ </tex-math></inline-formula> dBm power handling. We circumvent these issues through: 1) the concept of frequency-translational higher order N-path filters that uses baseband/intermediary-frequency nodes/resonators to break the trade-off between operating frequency and loss/power consumption; 2) a new complementary Nakagome-charge-pump-based clock booster circuit to enhance the power handling of the N-path filters; and 3) the usage of N-phase paths with overlapping local oscillator (LO’s) to enable a higher frequency of operation. When combined, these innovations have resulted in a higher order N-path band-pass filter that emulates the transmission profile of a third order elliptical bandpass filter (BPF) with two shunt resonators and two series resonators. Our prototype was implemented in a standard 65 nm CMOS process and operates across a wide frequency range of 1–5 GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${>}4 \times $ </tex-math></inline-formula> better than prior works). Measurements resulted in +8.8 dBm in-band <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$IP_{1\text {dB}}$ </tex-math></inline-formula> , +23 dBm in-band IIP3, +9.3 dBm out-of-band (OOB) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{1\text {dB}}$ </tex-math></inline-formula> , +36 dBm OOB IIP3, +15 dB selectivity one bandwidth away, and +24 dB OOB rejection at far out frequencies.