Analysis and Design of N-Path Filter Offset Tuning in a 0.7–2.7-GHz Receiver Front-End

Abstract

N-path techniques have become a popular candidate alternative to external pre-selection filtering in wireless receivers. Their main attraction lies in enabling tunable on-chip high-filters, with straightforward migration from one CMOS node to another. However, parasitic capacitance at the N-path filter input offsets the bandpass response from the desired center frequency in wideband circuits. In this paper, we focus on an LNA-first receiver and show that the offset at the LNA output varies in magnitude depending on LNA and filter load impedance properties. An offset-tuning approach is then evaluated for its effects on receiver gain and noise and to obtain design guidelines. We propose a digitally controllable implementation that preserves front-end gain and linearity, with a small penalty on receiver NF. A programmable 0.7-2.7-GHz front-end in 40-nm CMOS verifies the functionality. At 1.7 GHz, the front-end has a gain of 37 dB, a NF of 5.2 dB, and an out-of-band IIP3 of 1 dBm. Mikko Kaltiokallio (S'07-M'13) received the M.Sc. degree in electrical engineering from the Helsinki University of Technology, Espoo, Finland, in 2006. In 2014 he received the D.Sc. degree in the same field at Aalto University, Espoo, Finland. From 2005 to 2013, he was with the Electronic Circuit Design Laboratory, Helsinki University of Technology and later Aalto University. Since 2013, he has been with the Nokia Corp. working with front-end circuits. His research interests lie in the wideband high-linearity radio front-ends, mixed-signal RF and baseband design, and quadrature and LO buffering circuits. Kari Stadius (S'95-M'03) received the M.Sc., Lic. Tech., and D.Sc. degrees in electrical engineering from the Helsinki University of Technology, Helsinki, Finland, in 1994, 1997 He is currently working as a staff scientist at the Department of Micro-and Nanosciences, Aalto University School of Electrical Engineering, Finland. His research interests include CMOS RF circuits for communications with special emphasis on frequency synthesis, analog and mixed-mode circuit design, and new emerging RF technologies such as graphene. He has authored or coauthored over 70 refereed journal and conference papers in the areas of analog and RF circuit design.Kimmo Koli (M'95) was born in Karuna, Finland, in 1964. He received his M.Sc., Licentiate in Technology, and D.Sc. degrees in electrical on audio and sensor interfaces and wireless tranceivers. From 2008 to 2013, he joined STMicroelectronics (later ST-NXP Wireless and ST-Ericsson) and is currently with Ericsson, Turku, Finland, focusing on RF design blocks for wireless applications.Dr. Koli has authored or coauthored over 40 journal articles and conference papers and holds several patents. He has served for several years as a member of the technical program committee of IEEE International Solid-State Circuits

Broadband Synthetic Transmission-Line N-Path Filter Design

“…(16)] matches the T-line N-path filter simulation well. The approaches as increases (15), as illustrated in Fig. 10.…”

“…The asymmetry of the passband in Fig. 9 of the T-line N-path filter arises from the second natural frequency occurring at a higher frequency offset than the first natural frequency and is predicted by (15). A comparison of a simulation of Fig.…”

“…Additionally, the traditional passive N-path filter's transfer function is generally limited to two poles, reducing the filter's effectiveness for spectrally near-by jammers. Moreover, the switch parasitic capacitance creates a frequency offset, shifting the peak bandpass response to a lower frequency [15]. Recent work has demonstrated higher order active gyrator N-path filter approaches [13], [14]; however, due to the active nature of the designs, the power handling is still limited by the compression of the gyrators composed of resistive feedback amplifiers.…”

A SAW-less receiver front-end with continuously variable bandwidth and enhanced blocker-filtering

“…Taking LTE for example, its channel bandwidth contains 1.5/3/5/10/15/20 MHz. The bandwidths of SAWless receiver front-end in previous works are either fixed [3,7,10,12,13,14] or can only be configured discretely which makes it difficult to achieve an accurate value [4,5,9,11,15]. Without precise RF channel selection, the adjacent channel interference could seriously degenerate the performance of SAW-less receiver.…”

Analysis of imperfections in N-phase high-Q band-pass filters

“…The function of N-path filters have also been mathematically verified by two schools of thought, one pertaining to linear time-variant analysis [2], [5], [6] and the other using impedance transformation property [4], [7]. N-path filtering has been widely used in modern transceivers, especially in the past two years [10]- [14]. However, there are three main drawbacks associated with N-path filters.…”