Interference Mitigation in Reconfigurable RF Transceivers
At radio frequencies, there has been significant interest in the conception of a single radio that can be reconfigured dynamically in software to function across multiple standards, frequency bands and applications. The challenge associated with a truly reconfigurable radio is not in the design of the RF integrated circuit, but rather is in the front-end filters. Conventional radios employ front-end electro-acoustic filters to eliminate out-of-band interference, but these filters cannot be tuned across frequency bands and applications. While tunable filter technologies are under investigation, they exhibit higher loss and consequently are designed to exhibit less filtering to keep loss in check. As a result, the RF transceiver IC in a reconfigurable radio must operate under significantly higher interference levels. Furthermore, as we move towards highly-integrated radios in small form factors, the biggest source of interference in radio receivers are other transmitters in the same platform, whether it is a transmitter (TX) sharing an antenna with the receiver (RX) through a duplexer for frequency-division-duplex (FDD) applications or simply other transmitters whose antennas couple to the antenna of the receiver in question. To mitigate this self-interference problem, CoSMIC lab has developed novel interference cancellation techniques within reconfigurable transmitters and receivers. We developed a novel low-noise active self-interference cancellation technique that is able to cancel >0dBm transmitter leakage at the input of a wideband receiver with theoretically no addition of noise or distortion. This is accomplished by embedding the cancellation circuitry within a wideband noise- and distortion-cancelling low-noise amplifier, resulting in a Noise-and-Leakage Canceling Receiver (NLC-RX). The technique was also extended to cancel transmitter noise in the receiver band in addition to transmitter leakage. A 0.3-1.7GHz blocker-tolerant noise- and leakage-canceling 65nm CMOS receiver employing this technique was recently reported by our group [1]. The receiver achieves a triple beat at +2dBm peak TX leakage of 68dB and an effective IIP3 under TX leakage of +33dBm, representing increases of 38dB and 19dB respectively over the performance in the absence of cancellation [1],[2]. This represents the state of the art for linearity in CMOS receivers in the presence of modulated self-interference.
In addition, on the topic of on-chip tunable higher-order filters, our group has investigated N-path filters as a mean of realizing highly-linear, high-Q tunable on-chip filters. The original N-path filter topology only results in a second-order filtering profile which may not be sufficient for many applications. Recent research efforts to realize higher-order N-path filter responses have relied on the incorporation of active circuitry in the filter topology, where the power handling/linearity is limited to that of the active circuitry.
CoSMIC lab has developed a design methodology using only passive elements to synthesize N-path filters of arbitrary order and type. The methodology extends known filter synthesis techniques for LC filters to N-path implementations. A 600-850MHz 6th-order 65nm CMOS prototype has been designed and fabricated based on this methodology by our group which is reported in [3]. The filter achieves 35% tuning range with loss varying from 4.7-6.2dB and bandwidth ranging from 9-15MHz, in-band (IB)/out-of-band (OOB) P1dB of 1dBm/+14dBm and an IB/OOB IIP3 of +7dBm/+17.5dBm.
[1] Jin Zhou, Peter R. Kinget and Harish Krishnaswamy, "A Blocker-Resilient Wideband Receiver with Low-Noise Active Two-Point Cancellation of >0dBm TX Leakage and TX Noise in RX Band for FDD/Co-Existence," in 2014 IEEE ISSCC Dig. Tech. Papers, pp. 352-353, Feb. 2014.
[2] Jin Zhou, Peter R. Kinget and Harish Krishnaswamy, "Low-Noise Active Cancellation of Transmitter Leakage and Transmitter Noise in Broadband Wireless Receivers for FDD/Co-Existence," invited and submitted to IEEE Journal of Solid-State Circuits.
[3] Negar Reiskarimian and Harish Krishnaswamy, "Design of all-passive higher-order CMOS N-path filters," in 2015 IEEE Radio Frequency Integrated Circuits Symposium (RFIC), vol., no., pp.83-86, May 2015.
CoSMIC lab has developed a design methodology using only passive elements to synthesize N-path filters of arbitrary order and type. The methodology extends known filter synthesis techniques for LC filters to N-path implementations. A 600-850MHz 6th-order 65nm CMOS prototype has been designed and fabricated based on this methodology by our group which is reported in [3]. The filter achieves 35% tuning range with loss varying from 4.7-6.2dB and bandwidth ranging from 9-15MHz, in-band (IB)/out-of-band (OOB) P1dB of 1dBm/+14dBm and an IB/OOB IIP3 of +7dBm/+17.5dBm.
[1] Jin Zhou, Peter R. Kinget and Harish Krishnaswamy, "A Blocker-Resilient Wideband Receiver with Low-Noise Active Two-Point Cancellation of >0dBm TX Leakage and TX Noise in RX Band for FDD/Co-Existence," in 2014 IEEE ISSCC Dig. Tech. Papers, pp. 352-353, Feb. 2014.
[2] Jin Zhou, Peter R. Kinget and Harish Krishnaswamy, "Low-Noise Active Cancellation of Transmitter Leakage and Transmitter Noise in Broadband Wireless Receivers for FDD/Co-Existence," invited and submitted to IEEE Journal of Solid-State Circuits.
[3] Negar Reiskarimian and Harish Krishnaswamy, "Design of all-passive higher-order CMOS N-path filters," in 2015 IEEE Radio Frequency Integrated Circuits Symposium (RFIC), vol., no., pp.83-86, May 2015.
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