Tx Leakage Canceller Research Articles

A Low-Noise and Fast-Settling UHF RFID Receiver With Digitally Controlled Leakage Cancellation

UHF RFID reader suffers from a strong transmitter (Tx) leakage signal coupled to a receiver (Rx), especially for an area-compact single-antenna implementation. Then, several Tx leakage cancellation schemes have been developed not to saturate the Rx and to minimize the performance degradation. This brief proposes a UHF RFID reader Rx with a low noise performance and a fast settling time by employing a digitally controlled leakage cancellation method in both passive and active realizations. A digitally-controlled passive vector reflector enhances the Tx to Rx isolation ratio by providing the optimum load impedance. An active anti-leakage feedback loop adaptively tracks the time-varying leakage and generate the phase-inverted leakage replica to suppress the leakage. The prototype chip is fabricated in a CMOS 55 nm process and the area of the chip is 2.1 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.8$ </tex-math></inline-formula> mm. The passive leakage cancellation (PLC) with a vector reflector endures the 1 dBm leakage with a low Rx noise figure of 12.5 dB and 35.7 mW power consumption. The active leakage cancellation (ALC) with an anti-leakage feedback loop covers 6 dBm leakage with a fast settling time of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.6~\mu \text{s}$ </tex-math></inline-formula> and 58 mW power consumption.

A Frequency Selective Feedback Receiver for Multi‐Bands Operation

AbstractFor a frequency‐division duplex (FDD) wide‐band code‐division multiple‐access (WCDMA) system, transmit (TX) signal leakage at the receiver input degrades the receiver performance. To cancel this TX leakage, a frequency selective feedback was previously proposed, but it had an unpredictable feedback loop characteristic due to the uncertainty of the duplexer impedance. This paper presents a new method to achieve TX leakage cancellation regardless of the duplexer impedance. In addition, a local oscillator (LO) phase shift technique is proposed to apply this method for multi‐band. A receiver adopting these proposed techniques is implemented using a 0.18‐μm CMOS process to prove the concept. The measured TX attenuations of the high‐ and low‐band are 17‐dB and 20‐dB, respectively, and the measured noise Figure (NF) degradations of the high‐ and low‐band are 0.6‐dB and 0.5‐dB, respectively. The measurement results demonstrate effectiveness of the proposed techniques.

Quasi-Circulator Using an Asymmetric Coupler for Tx Leakage Cancellation

A quasi-circulator is proposed by using an asymmetric coupler with high isolation between the transmitting (Tx) and receiving (Rx) ports. The proposed quasi-circulator consists of quarter-wave transmission lines, which have unbalanced characteristic impedances and the terminated port, which is purposely unmatched with the reference impedance in the coupler. The port compensates for the asymmetric impedances of the coupler using the proposed design parameter. Because of its asymmetric structure and the usage of the unmatched port, the proposed circulator can be accurately designed to have high Tx–Rx isolation without increasing the signal losses in the Tx and Rx paths at the operating frequency. The proposed quasi-circulators show isolation improvements of 9.07 dB at 2.45 GHz and 7.95 dB at 24.125 GHz compared with conventional circulators using the symmetric couplers. The characteristic improvement of the proposed quasi-circulator was demonstrated by the increase of the detectable range of the 2.45 GHz Doppler radar sensor with the quasi-circulator.

Low-Noise Active Cancellation of Transmitter Leakage and Transmitter Noise in Broadband Wireless Receivers for FDD/Co-Existence

A technique for active cancellation of transmitter self-interference in wideband receivers is presented. The active TX leakage cancellation circuitry is embedded within a noise-cancelling low-noise transconductance amplifier (LNTA) so that the noise and the distortion of the cancellation circuitry are cancelled, resulting in a noise-cancelling, self-interference cancelling receiver (NC-SIC RX). A second-point cancellation of TX noise in the RX band is performed after the LNTA so that the noise impact of the second canceller is reduced. Theoretical analyses related to the benefits and limits of active self-interference cancellation as well as the simultaneous cancellation of the noise and distortion of the cancellation circuitry are presented. A 0.3-1.7 GHz receiver with the proposed active cancellation is implemented in 65 nm CMOS. The proposed scheme can cancel up to +2 dBm peak TX leakage at the receiver input. The triple beat at +2 dBm peak TX leakage is 68 dB and the effective IIP3 is +33 dBm, representing increases of 38 and 19 dB, respectively, over the receiver without cancellation. The associated increase in receiver NF is less than 0.8 dB. In addition, the scheme effectively suppresses TX noise in RX band by up to 13 dB. The technique can be more generally viewed as an active combining structure that has ideally no noise penalty and is able to handle large signals without generating distortion and can be applied to any scenario where a replica of an interference signal can be generated.

An LTCC multilayer packaged 24‐Ghz short‐range radar with an embeded Tx leakage canceller

AbstractThe high isolation performance of a Tx leakage canceller was demonstrated using low temperature cofired ceramics (LTCC) technology. The Tx‐to‐Rx isolation of −52 dB was achieved at 24.15 GHz. The parasitic effects of the Tx leakage canceller were studied for the purpose of reducing Tx leakage. A method involving the vertical stacking of a three‐dimensional LTCC packaging module and an FR‐4 substrate was developed, and a compact 24‐GHz quadrature Doppler radar front‐end module was fabricated. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:671–677, 2014

A compact 24 GHz quadrature Doppler radar with front-end MMIC

A compact 24 GHz quadrature Doppler radar front-end monolithic microwave integrated circuit (MMIC) with Tx leakage canceller is developed. The chip is 3 × 2 mm2 and the front-end module is 3 × 3 cm2. The MMIC consists of a 24 GHz voltage-controlled oscillator, a Tx leakage canceller and two mixers. The radar module can measure speeds as low as 2.5 mm/s, which corresponds to a 0.41 Hz Doppler shift. The quadrature topology enables the signs of a Doppler shift to be detected and obviates the null point problems.

A CMOS Transmitter Leakage Canceller for WCDMA Applications

A transmitter (TX) leakage canceller is proposed for improving the dynamic range of the receiver (RX) for wideband code division multiple access applications. A TX leakage canceller circuit in this paper is simple in implementation and has low noise figure (NF) contribution. It is a feed-forward canceller that samples a reference signal from the TX output and injects the amplitude-adjusted and phase-rotated signal to the RX chain. The canceller circuit is integrated with a low-noise amplifier and implemented in a 0.18-μm CMOS technology. A cancellation of 23 dB is achieved with only 10-mA current consumption increase and low NF increase.

A CMOS wideband LNA with low-loss integrated TX leakage canceller

A CMOS wideband LNA with low-loss integrated TX leakage canceller

24 GHz Balanced Doppler Radar Front-End With Tx Leakage Canceller for Antenna Impedance Variation and Mutual Coupling

A new balanced Doppler radar front-end architecture with Tx leakage canceller for antenna impedance variation and antenna mutual coupling is proposed. Consisting of two quadrature hybrids, two ring hybrids and 4-port feed antenna system, the proposed balanced structure achieves high transmit/receive (Tx/Rx) isolation stable to antenna impedance variation and antenna mutual coupling. The proposed 4-port feed antenna is configured by dual fed 2 × 1 patch array having 6.97 dBi and 5.65 dBi of measured Tx and Rx peak gain, respectively. In addition, the proposed architecture undergoes no power loss in both transmit and receive paths, and obtains the measured Tx/Rx isolation of more than 45 dB stable at 24 GHz regardless of the load variation. The proposed architecture that can determine the speed as low as 0.5 mm/s (0.078 Hz Doppler shift) is theoretically and experimentally analyzed for high isolation despite of antenna mismatch.

오토트랜스포머를 이용한 RFID용 CMOS 송신 누설 신호 제거기

본 논문에서는 UHF RFID 리더에서의 오토트랜스포머를 이용한 가변 송신 누설 신호 제거기를 제안하였다. 제안된 송신 누설 신호 제거기는 오토트랜스포머와 디지털 가변 캐패시터, 가변 저항, 보상 증폭기로 구성되었으며, 0.13 <TEX>${\mu}m$</TEX> 1-폴리 6-메탈 RF CMOS 공정을 사용하여 설계되었다. 시뮬레이션 결과, 제안된 구조는 송신단에서 수신단으로 신호가 전송될 때 55 dB 이상의 송신 누설 신호 제거도를 보이며, 2.5 dB의 수신 삽입 손실을 갖는다. 송신 누설 신호 제거 회로는 825 MHz에서 985 MHz까지 디지털 주파수 조정이 가능하며, CMOS 공정으로 집적될 수 있다. In this paper, a tunable integrated transmitter leakage canceller based on an autotransformer for ultra-high-frequency (UHF) RFID readers is presented. The proposed TX leakage canceller consists of an autotransformer, a digital tuning capacitor, a voltage controlled tuning resistor, and a compensating amplifier, and it is designed using 0.13 <TEX>${\mu}m$</TEX> 1-poly 6-metal RF CMOS process. The simulation results show that the proposed structure has over 55 dB rejection characteristic between a transmitter and a receiver and a 2.5 dB of the RX insertion loss. The TX leakage canceller can be digitally tuned from 825 MHz to 985 MHz with the tuning capacitor and it can be fully integrated.

24-GHz transceiver patch array front-end with a balanced Tx leakage canceller

A new 24-GHz transceiver patch array with a balanced Tx leakage canceller insensitive to antenna impedance variation and mutual coupling among ports is proposed. Consisting of two quadrature hybrids, two ring hybrids, and 4-port feed antenna, high transmit/receive (Tx/Rx) isolation is maintained regardless of antenna impedance variation and antenna mutual coupling. The proposed 4-port feed antenna is configured by dual fed 2x1 patch array having 6.12 and 5.06 dBi of measured Tx and Rx peak gain, respectively. In addition, the proposed architecture undergoes no power loss because of load termination (usually 50 Ω) in both transmit and receive paths. The proposed architecture obtains the measured Tx/Rx isolation of more than −40 dB stable at 24 GHz regardless of the antenna impedance variation. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:559–562, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25815

Transmitter and Receiver Isolation by Concentric Antenna Structure

A concentric antenna structure with transmitter (Tx) and receiver (Rx) isolation characteristic is proposed. For both cases that Tx and Rx use the same frequency or different frequencies, Tx leakage can be removed by the proposed antenna structure. The field couplings between antennas are mathematically presented and Tx leakage cancellation is theoretically examined. To theoretically verify the case that Tx and Rx use the same frequency, a set of 16 inverted-F antennas and a set of 4 inverted-F antennas are designed for Tx and Rx, respectively. For the case that Tx and Rx use different frequencies, a set of 4 monopole antennas is designed for Tx and Rx each. The measured result shows the Tx/Rx isolation characteristic of more than -50 dB.

A Circularly Polarized Balanced Radar Front-End With a Single Antenna for 24-GHz Radar Applications

In this paper, we propose a circularly polarized balanced radar front-end topology with a Tx leakage canceller. This radar is composed of a dual-orthogonal fed microstrip patch antenna, a 90deg delay line, a differential cross-coupled oscillator, two Lange couplers, a Wilkinson combiner, and a mixer. We implemented circularly polarized balanced Doppler radars by using a printed circuit board and InGaP/GaAs heterojunction bipolar transistor technologies. The front-end chip and module with antenna are 1 mm times 1 mm and 3 cm times 3 cm, respectively. The average Tx-to-Rx isolation is about 36 dB. This radar can measure speeds as low as 0.5 mm/s, which corresponds to a 0.076-Hz Doppler shift. The received signals of the circularly polarized balanced Doppler radar are about two times larger than those of a linearly polarized balanced Doppler radar due to the topology. This result occurs because the proposed radar has an intrinsic loss of only 3 dB in the receiving path.

TX Leakage Cancellation via a Micro Controller and High TX-to-RX Isolations Covering an UHF RFID Frequency Band of 908–914 MHz

A transmitter (TX) leakage cancellation scheme using a micro controller (MCU) is introduced. This letter highlights an adaptive anti-leakage signal generation via an MCU, which plays the key role in reducing the TX leakage signal level. High transmitter-to-receiver (TX-to-RX) isolation is verified with measurement results.

Adaptive TRX isolation scheme by using TX leakage canceller at variable frequency

AbstractThis article presents a TX leakage cancellation scheme for UHF RFID readers. A prototype is implemented on a UHF RFID reader board, which includes a circulator, directional coupler, microcontrol unit (MCU)‐controlled variable attenuator, and phase shifter. The difference between a conventional TX leakage canceller and this new one is that, reflected signals caused by mismatches between the front‐end and the antenna are included; in addition, high isolation is supplemented at variable frequencies. About 10% of the frequency range is recovered by the best suited parameter values that provide a predetermined process of MCU; and thus, peak isolation characteristics are constantly guaranteed at each center frequency by phase‐shifted signal generation that follows references stored in MCU. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2043–2045, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23592

A Quadrature Radar Topology With Tx Leakage Canceller for 24-GHz Radar Applications

A quadrature radar topology with a Tx leakage canceller is presented. The canceller is composed of four branch-line hybrid couplers, a 90deg delay line, and a Wilkinson combiner. It has high Tx-to-Rx isolation and wide bandwidth characteristics. The isolation is 35.27 dB at 24 GHz and does not drop below 30 dB over a 2-GHz bandwidth. Given that the isolation of the branch-line hybrid coupler is 21.5 dB, the enhancement of the isolation is expected to be 13.77 dB. A quadrature Doppler radar front-end with the canceller was implemented. The noise level in the mixer output is lower by 9 dB compared with that of a conventional quadrature radar. This radar can measure speed as low as 0.76 mm/s, which correspond to a 0.12-Hz Doppler shift. It is also able to detect signs of the Doppler shift from a moving target due to its quadrature topology.