Image Rejection Ratio Research Articles

ADAPTIVE COMPLEX FILTERS BASED TRANSMITTER IQ IMBALANCE REJECTION

This paper presents an efficient method for compensation of frequency-dependent (FD) transmitter In-phase Quadrature (IQ) imbalance. Proposed method compensates imbalance by exploiting indirect learning architecture (ILA) and complex filters whose coefficients are determined in an iterative process. Compensation performance is assessed after the method has been implemented in a Software Defined Radio (SDR) platform, capable of transmitting modulations at different central frequencies. Measured results demonstrate that the imbalance related images are reduced down to the noise floor. After applying the proposed IQ imbalance correction method, the transmitter image rejection ratio (IRR) is increased by 15dB in the case of an SDR transmitter operating at central frequency of 1.7 GHz. The ADC/DAC sampling rate is 61.44MS/s, while the signal bandwidth, for which the compensation is performed, is 30.72MHz. The advantage of the proposed method is low complexity in terms of a reduced number of coefficients. The method is generic and can be utilized for IQ imbalance compensation when wideband signals are transmitted.

A Microwave Photonic Channelized Receiver Based on Polarization-Division Multiplexing of Optical Signals

Aimed at the problems of optical frequency combs, such as their large number of comb lines, their high flatness, and their lack of ease in generating, as well as the fact that the channelization efficiency of the scheme based on optical frequency combs is low, we proposed a microwave photonic channelization receiver based on signal polarization multiplexing. Using two-line local optical frequency combs with different frequencies to demodulate the RF signal in the orthogonal polarization state, 16 sub-channels with a bandwidth of 1 GHz can be received simultaneously. The experimental results show that the image rejection ratio can reach 28 dB, and the third-order spurious-free dynamic range of the system can reach 96.8 dB·Hz2∕3. This scheme has the advantages of a large number of sub-channels and a high channelization efficiency; it has great application potential in broadband wireless communication, radar, and electronic warfare systems.

Multiplier-less Broadband and Linear Phase Digital Hilbert Transformers

The Hilbert transformation for generating the analytic signal or signal envelope is widely used in modern communication receivers, in radar and sonar systems. It introduces a 90∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$90^{\\circ }$$\\end{document} phase shift of the input signal. Since the impulse response of the ideal Hilbert transformer is non-causal, it must be approximated by an FIR or IIR filter. This paper shows results of novel algorithms for designing broadband digital IIR Hilbert transformers and its implementation. The designs employ Galerkin or collocation techniques. The transfer function of the Hilbert transformer is a rational polynomial of low order and exhibits approximately linear phase. The filters match the 90∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$90^{\\circ }$$\\end{document} phase shift requirement of Hilbert transformers almost perfectly and exhibit approximately constant group delay in the passband. The achieved image rejection ratio is typically larger than 50 dB. The quantization of the filter coefficients is realized by a Canonical Signed Digit (CSD) representation, reducing the hardware resources compared with two’s complement. The resulting filters are multiplier-less, which is crucial for high-speed signal processing and low power consumption. The design techniques and the CSD representation are realized in a MATLAB toolbox. The filters were moreover implemented in VHDL and SystemC. Additionally, a MATLAB tool for automatically generating a VHDL package containing the filter parameters has been implemented.

Frequency down-conversion system with image rejection using thin film lithium niobate parallel modulation phase-shifting structure

The frequency down-conversion system based on microwave photonics has been widely employed in radar, electronic warfare, and satellite communication systems. In this paper, we propose an image rejection frequency down-conversion system, wherein the phase modulator and phase shifter are integrated on thin film lithium niobate platform. The working principle is elucidated through the establishment of a theoretical model. Subsequently, the system successfully down-converts a 40 GHz radio frequency (RF) signal to a 5 GHz intermediate frequency signal, achieving an image rejection ratio of approximately 30 dB. Simultaneously, varying degrees of image rejection are observed for different RF signals. The system maintains robust image rejection performance across varying RF and image signal power, as well as different levels of input optical power.

A Hybrid Scheme for TX I/Q Imbalance Self-Calibration in a Direct-Conversion Transceiver

A generic transmitter (TX) I/Q imbalance self-calibration method, which was designed based on a hybrid analog and digital structure, is proposed in this paper. The whole calibration scheme was implemented using low-complexity digital–analog circuits based on a zero-force feedback loop. In order to eliminate the negative effect of local oscillator (LO) harmonics on the calibration, we used a variable-delay line (VDL) in the analog domain instead of the digital phase compensator. The prototype chip was fabricated within a 0.2∼5.0 GHz direct-conversion transmitter in a 65 nm CMOS process, and measurements found an image rejection ratio (IRR) of 65 dBc.

A 28 GHz Highly Linear Up-Conversion Mixer for 5G Cellular Communications

In this paper, we present a highly linear direct in-phase/quadrature (I/Q) up-conversion mixer for 5G millimeter-wave applications. To enhance the linearity of the mixer, we propose a complementary derivative superposition technique with pre-distortion. The proposed up-conversion mixer consists of a quadrature generator, LO buffer amplifiers, and an I/Q up-conversion mixer core and achieves an output third-order intercept point of 15.7 dBm and an output 1 dB compression point of 2 dBm at 27.6 GHz, while it consumes 15 mW at a supply voltage of 1 V. The conversion gain is 11.4 dB and the LO leakage and image rejection ratio are −56 dBc and 61 dB, respectively, in the measurement. The proposed I/Q up-conversion mixer is suitable for 5G cellular communication systems.

ALMA Band 9 upgrade: A feasibility study

We present the results of a study on the feasibility of upgrading the existing ALMA Band 9 receivers (602-720 GHz). In the current configuration, each receiver is a dual channel heterodyne system capable of detecting orthogonally polarized signals through the use of a wire grid and a compact arrangement of mirrors. The main goals of the study are the upgrade of the mixer architecture from Double-Sideband (DSB) to Sideband-separating (2SB), the extension of the IF and RF bandwidth, and the analysis of the possibilities of improving the polarimetric performance. We demonstrate the performance of 2SB mixers both in the lab and on-sky with the SEPIA660 receiver at APEX, which shows image rejection ratios exceeding 20 dB and can perform successful observations of several spectral lines close to the band edges. The same architecture in ALMA Band 9 would lead to an increase in the effective spectral sensitivity and a gain of a factor two in observation time. We set up also an electromagnetic model of the optics to simulate the polarization performance of the receivers, which is currently limited by the cross-polar level and the beam squint, i.e. pointing mismatch between the two polarizations. We present the results of the simulations compared to the measurements and we conclude that the use of a polarizing grid is the main responsible of the limitations.

Microwave photonic I/Q mixer for wideband frequency downconversion with serial electro-optical modulations.

In this paper, we propose a serial electro-optical (EO)-modulation-based microwave photonic in-phase and quadrature (I/Q) mixer and investigate its performance for wideband frequency downconversion. The proposed I/Q mixer uses two EO modulators and a programmable optical processor in a serially cascaded structure, which ensures good phase stability and flexibility to achieve high-performance broadband frequency downconversion. A proof-of-concept experiment is carried out in which the frequency downconversion of the RF signals in the range from 10 to 40 GHz is demonstrated with an average image rejection ratio of 38.66 dB. The spurious-free dynamic range (SFDR) measured at around 15 GHz is 86 dBc·Hz2/3. Based on this microwave photonic I/Q mixer, a broadband radar receiver is established and de-chirping of linearly frequency modulated (LFM) radar echoes with an instantaneous bandwidth of 8 GHz (10-18 GHz) is achieved. The results verify its feasibility for high-performance I/Q mixing in practical applications.

A S-band switchless bi-directional transceiver with a 52% fractional bandwidth in CMOS technology

This paper presents a bi-directional switchless wideband transceiver front-end for S-band multi-functional digital array system. In an S-band digital array system, a silicon-based RF front-end module requires a high integration level, compact size, large bandwidth, and low power consumption features. A bi-directional switchless transceiver could provide a compact solution. However, the shared RF matching network in such a transceiver is crucial due to its influence on Rx sensitivity, Tx output power, TRx isolation, and bandwidth. This work proposes a compact π matching network for simultaneous broadband Rx noise matching, Tx power matching, and TRx isolation. Also, a double quadrature down-conversion architecture is proposed to improve image signal rejection in the whole S-band. Therefore, false detection in the S-band digital array can be avoided. Fabricated in a 0.18μm CMOS technology, this S-band transceiver occupies a silicon area of 3.2 × 2 mm2. In the Rx mode, the measured gain is 20.7–28 dB in 2–4 GHz at 25 °C. The RX noise figure is 9.5–11.5 dB, and the input 1-dB compression point is -11 dBm. In the Tx mode, the gain is 16.5–19.6 dB in 2–4 GHz at 25 °C, and Psat is 10.2 dBm. The RX bandwidth is 2–3.4 GHz, while that of Tx is 2–4 GHz. The corresponding fractional bandwidth is 52% and 67%, respectively. Furthermore, this transceiver shows an image rejection ratio of 28.9–41.4 dB suppression at the operation frequency band.

A 0.45‐V low‐power low‐noise amplifier using a wideband image‐rejection technology

AbstractA 0.45‐V low‐power wideband image‐rejection low‐noise amplifier (LNA) using Taiwan Semiconductor Manufacturing Company (TSMC) 0.18‐μm CMOS process has been proposed. The supply voltage, power consumption and chip area of the proposed LNA can be reduced using forward body biasing, folded cascode topology and a feedback capacitor. Moreover, a wideband gain‐enhancement‐and‐image‐rejection (WGEIR) circuit including a variable resonant LC tank and a common‐gate amplifier has been developed. The inductance of the variable resonant LC tank can enlarge the gain of the proposed LNA. The capacitance of the variable resonant LC tank can achieve the image rejection. Using the WGEIR circuit, gain enhancement and wideband image rejection can be achieved simultaneously. The variable inductors and capacitors are developed for suppressing wideband image signals and good image rejection ratio (IRR). The combination of the variable inductors and capacitors can achieve eight image‐reject frequencies under three control voltages. The proposed LNA shows the measured results including a 10‐dB power gain, a 3‐dB noise figure (NF) and a −11‐dBm input third‐order intercept point (IIP3) at 2.4 GHz, respectively. The measured IRR ranges from 18 to 23 dBc around 3.6–4.5 GHz, which is 900‐MHz image‐reject bandwidth. The measured proposed LNA using the mentioned techniques consumes 0.8‐mW power.

High cost-effective photonic assisted in-band interference cancellation scheme for centralized radio access network towards future 5G communication

A photonic-assisted scheme capable of self-interference cancellation (SIC) and image rejection mixing (IRM) is demonstrated to solve the intractable problem of in-band interference for in-band full duplex (IBFD) systems with high frequency and large bandwidth. In the proposed scheme, a single optical path configuration is constructed based on an integrated modulator applied as the main device. The SIC operation is implemented in the optical domain making it immune to the influence caused by fiber dispersion. Owing to the intermediate frequency (IF) signal amplitude regulation mechanism under the combined action of fiber dispersion induced phase and double sideband (DSB) modulation, the scheme can realize IRM without increasing the system complexity. Experimental results show that the 50 MHz 16-quadrature amplitude modulation (16-QAM) signal of interest (SOI) centered at different frequencies are down-converted to 2.5 GHz. The depth of SIC and image-rejection (IR) is over 35 dB and 25 dB after transmitted through a span of 10.1 km optical fiber. The received 16-QAM down-converted signal can be recovered with an error vector magnitude (EVM) which satisfies the requirement of 3GPP-specified EVM limit. The signal recovery performance, SIC depth and image rejection ratio (IRR) under different signal to interference ratio (SIR) is also investigated. In addition, a comparison of relevant literature with this scheme from the perspective of technical discussion is also presented. The proposed scheme can realize effective functional integration with compact structure, simple parameter tuning mechanism, improved stability and high cost-effectiveness to solve the in-band interference problem which is of great value to be applied in IBFD centralized radio access networks (CRAN) towards future 5G communication.

Photonics-Based Broadband Radar With Coherent Receiving for High-Resolution Detection

A microwave photonics radar with interference-suppressed high-resolution detection ability is proposed and experimentally demonstrated based on optical frequency quadrupling and coherent receiving de-chirping. Which is achieved by using a dual-parallel Mach-Zehnder modulator to perform base-band signal frequency quadrupling in transmitter, and an optical coherent receiver to realize balanced photonic in-phase/ quadrature (I/Q) de-chirping of the broadband radar echoes in receiver. Thanks to the frequency multiplication, a wideband radar transmitting signal can be generated with low speed electron devices. Meanwhile, interference-free detection by suppressing undesired common-mode interferences and image frequency could be achieved with balanced photonic I/Q de-chirping broadband radar echoes. In the experiment, a photonics-based K-band radar with a bandwidth of 8 GHz is demonstrated, corresponding to a resolution better than 2.0 cm. In addition, the balanced photonic I/Q de-chirping receiver achieves an image-rejection ratio of 40.4 dB. The proposed radar detection system is a promising candidate in interference-suppressed high-resolution radar application.

A Q-Band CMOS Image-Rejection Receiver Integrated with LO and Frequency Dividers

This paper presents a Q-band image-rejection receiver using a 65 nm CMOS technology. For a high image-rejection ratio (IMRR), the Q-band receiver employs the Hartley architecture which consists of a Q-band low-noise amplifier, two down-conversion mixers, a 90° hybrid coupler, and two IF baluns. In addition, a Q-band fundamental voltage-controlled oscillator (VCO) and a frequency divider chain divided by 256 are integrated into the receiver for LO. A charge injection technique is employed in the mixers to reduce the DC power while maintaining a high conversion gain and linearity. The VCO adopts a cross-coupled topology to secure stable oscillation with high output power in the Q-band. The frequency divider chain is composed of an injection-locked frequency divider (ILFD) and a multi-stage current-mode logic (CML) divider to achieve a high division ratio of 256, which facilitates the LO signal locking to an external phase-locked loop. An inductive peaking is employed in the ILFD to widen the locking range. The Q-band image-rejection receiver exhibits a peak conversion gain of 16.4 dB at 43 GHz. The IMRR is no less than 35.6 dBc at the IF frequencies from 1.5 to 5 GHz.

Investigation of phase modulation and propagation-route effect from unmatched large-scale structures for Doppler reflectometry measurement through 2D full-wave modeling

To interpret the common symmetric peaks caused by the large-scale structure in the complex S(f) spectrum from the heterodyne Doppler reflectometry (DR) measurement in EAST, a 2D circular-shaped O-mode full-wave model based on the finite-difference time-domain method is built. The scattering characteristics and the influences on the DR signal from various scales are investigated. When the structure is located around the cutoff layer, a moving radial or poloidal large-scale structure k θ ≲ k θ,match (k θ,match is the theoretic wavenumber of Bragg scattering) could both generate an oscillation phase term called ‘phase modulation’, and symmetrical peaks in the complex S(f) spectrum. It was found that the image-rejection ratio A −1/A +1 (A ±1 represents the amplitudes of ±1 order modulation peaks) could be a feasible indicator for experiment comparison. In the case when the structure is near the cutoff layer with the same arrangement as the experiment for the edge DR channel, the curve of A −1/A +1 versus k θ can be divided into three regions, weak asymmetrical range with k θ /k 0 ≲ 0.15 (k 0 is the vacuum wavenumber), harmonics range with 0.15 ≲ k θ /k 0 ≲ 0.4, and Bragg scattering range of 0.4 ≲ k θ /k 0 ≲ 0.7. In the case when the structure is located away from the cutoff layer, the final complex S(f) spectrum is the simple superimposing of modulation and Bragg scattering, and the modulation peaks have an amplitude response nearly proportional to the local density fluctuation, called the ‘propagation-route effect’. Under the H-mode experiment arrangement for the core DR, a critical fluctuation amplitude ∼ 1.3–4.1 ( refers to the pedestal large-scale structure amplitude and Amp(n e,Tur.@MSA) refers to turbulence amplitude at the main scattering area) is needed for the structure in the pedestal to be observed by the core DR measurement. The simulations are well consistent with the experimental results. These effects need to be carefully considered during the DR signal analyses as the injecting beam passes through the plasma region with large-scale structures.

Wideband 120-GHz CMOS I/Q Transmitter With Suppressed IMRR and LOFT for Wireless Short-Range High-Speed 6G IoT Applications

In this study, a wideband 120-GHz I/Q transmitter with suppressed image rejection ratio (IMRR) and LO feedthrough (LOFT) is presented using 40-nm complementary metal oxide semiconductor technology. For the up-conversion mixer, an NMOS/PMOS pair with resistive feedback is used during the transconductance stage to increase the input bandwidth with gain boosting, and a novel switching core without LO-RF coupling is used to suppress the LOFT effect. For the quadrature injection locked tripler, an I/Q calibration circuit is inserted to minimize the I/Q mismatch; accordingly, the measured IMRR is greatly improved. The peak conversion gain of the proposed transmitter was 10.8 dB, and the 3-dB gain bandwidth was 20 GHz. The measured IMD2 and IMD3 were above 40 dBc. Moreover, the IMRR was measured as 43.1 dBc, applying I/Q calibration. The measured LOFT was 33.7 dBc. The data rate of the proposed transmitter was measured up to 20 Gbps and at a distance of 5 cm. Subsequently, the error vector magnitudes were 13.4 dB for QPSK and -19.1 dB for 16-QAM modulation. It is expected that such wireless high-speed communication can be applied to wireless short range high-speed 6G IoT applications.

Quadrature Wilkinson power divider using cross-type short-circuited shunt stub for good amplitude and phase balance

This paper introduces a new design of a quadrature 3-dB power splitter using a quadrature Wilkinson power divider and a cross-type short-circuited shunt stub for printed circuit board (PCB) circuit design. For 3-dB power splitting and a relative 90° phase difference, several types of quadrature 3-dB power splitters are commonly used in RF and microwave applications, including Lange coupler, directional coupler, branch-line coupler, and quadrature Wilkinson power dividers. Among them, quadrature Wilkinson power dividers often utilize a Schiffman phase shifter and λ/4 short-circuited shunt stubs for compensation circuit.In this paper, the aforementioned schemes have been evaluated by image rejection ratio (IRR) bandwidth (BW) related to amplitude and phase imbalance property. The new design of the quadrature Wilkinson power divider adopting the proposed cross-type short-circuited shunt stub offers superior −25-dB IRR BW compared with other quadrature 3-dB power splitters in PCB fabrication. In measurement, the proposed quadrature Wilkinson power divider provided a −25-dB IRR BW of 3.50 GHz, operating at a center frequency of 9.5 GHz. The designed power splitter offered an operating frequency of 2.64 GHz, satisfying −25-dB IRR BW, 10-dB impedance BWs, and 20-dB isolation BW.

A 52-to-57 GHz CMOS Phase-Tunable Quadrature VCO Based on a Body Bias Control Technique

This paper presents a 52-to-57 GHz CMOS quadrature voltage-controlled oscillator (QVCO) with a novel I/Q phase tuning technique based on a body bias control method. The QVCO employs an in-phase injection-coupling (IPIC) network comprising four diode-connected FETs for the quadrature phase generation. The I/Q phase error is calibrated by controlling the body bias voltage offset of the QVCO’s four core FETs. This technique effectively covers a wide range of I/Q phase error between −13.4° and +10.7°. It also minimally induces the unwanted variations in the phase noise, current dissipation, and oscillation frequency, which were found to be only 0.4 dB, 0.07%, and 36 MHz, respectively. After the IPIC-QVCO, a phase-tunable two-stage LO buffer employing a 3-bit switched-capacitor bank was added for additional phase tuning, leading to the extension of the phase tuning range up to −22.7–+20.0°. The proposed QVCO is implemented in a 40 nm RF CMOS process. The measured results show that the QVCO covers a frequency band from 52.4 to 57.6 GHz while consuming 26.2 mW. The phase noise and the figure-of-merit of the QVCO are −91.8 dBc/Hz at 1 MHz offset and −172.4 dBc/Hz, respectively. We also realized a fully integrated 55 GHz quadrature RF transmitter employing the phase-tunable QVCO and LO generator. The effectiveness of the proposed phase-tunable LO generator was confirmed by verifying the image rejection ratio (IRR) calibration at the RF output.

A Novel 180–210 GHz Single Sideband Mixer Using Filtering Waveguide-Microstrip Transition Structure

In this letter, we proposed a novel 180–210 GHz single sideband (SSB) Schottky diode-based subharmonic mixer (SHM), which features in simpler structure and fabrication compared with existing methods. Image rejection of the 220–250 GHz upper sideband (USB), as well as impedance matching, was achieved by a filtering waveguide-microstrip transition structure at the radio frequency (RF) input, rather than using traditional waveguide filters. Eventually, the mixer was measured to show great performance, including a SSB conversion loss (CL) of 8–12 dB across the passband, and an image rejection ratio (IRR) of 15–35 dB.

A Digital Frequency-Dependent I/Q Imbalance and Group Delay Estimation and Compensation Modules for mmWave Single Carrier Baseband Transceivers

This paper proposes the estimation and compensation modules of digital frequency-dependent (FD) I/Q imbalance and group delay for single carrier (SC) mode with 15 Gbps throughput rate in the millimeter-wave (mmWave) band. The proposed compensation module of a digital recursive filter can mitigate FD I/Q imbalance effects caused by the -3 dB corner imbalance of the reconstruction and anti-aliasing filters of I/Q branches. The proposed recursive filter with the appropriate initial coefficients based on the result of Golay sequence estimation can shorten the convergence time and precisely acquire the desired coefficients. The average image rejection ratio (IRR) performance after compensating by the proposed module can be improved from 21.97 dB to 47.54 dB. Besides, the group delay distortion in reconstruction and anti-aliasing filters will cause intersymbol interference to distort the in-band signal. We employ a digital equalization filter with the filter coefficients derived from the correlation results based on the Golay sequence to compensate the in-band group delay distortion. After the proposed group delay is pre-compensation at TX, the system-level performance of error vector magnitude (EVM) performance is improved by 6.21 dB to -27.78 dB to satisfy the IEEE 802.11ad/ay requirement in 64-QAM mode. The inner RX BER performance with the FD I/Q imbalance and the group delay compensation modules can achieve 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at 23 dB and also satisfy the system requirement at SNR of required 25.52 dB. A four-times parallelism architecture is proposed to work at a clock rate of 625 MHz with 64-QAM mode. The gate count and power consumption of the proposed design are 154.4 K and 16.2 mW, respectively.

Broadband photonic-assisted microwave receiver with high cross-channel interference suppression and image rejection.

A broadband photonic-assisted microwave receiver with high cross-channel interference suppression and image rejection is proposed and experimentally demonstrated. At the input of the microwave receiver, a microwave signal is injected into an optoelectronic oscillator (OEO), which functions as a local oscillator (LO) to generate a low-phase noise LO signal as well as a photonic-assisted mixer to down-convert the input microwave signal to the intermediate frequency (IF). A microwave photonic filter (MPF), realized by the joint operation of a phase modulator (PM) in the OEO and a Fabry-Perot laser diode (FPLD), is used as a narrowband filter to select the IF signal. Thanks to the wide bandwidth of the photonic-assisted mixer and the wide frequency tunable range of the OEO, the microwave receiver can support broadband operation. The high cross-channel interference suppression and image rejection are enabled by the narrowband MPF. The system is evaluated experimentally. A broadband operation from 11.27 to 20.85 GHz is demonstrated. For a multi-channel microwave signal with a channel spacing of 2 GHz, a cross-channel interference suppression ratio of 21.95 dB and an image rejection ratio of 21.51 dB are realized. The spurious-free dynamic range (SFDR) of the receiver is also measured to be 98.25 dB·Hz2/3. The performance of the microwave receiver for multi-channel communications is also experimentally evaluated.