Gain Imbalance Research Articles

A 1-V Wideband Low-Power CMOS Active Differential Power Splitter for Wireless Communication

A 1-V wideband CMOS phase and power splitter (PPS) with an RLC network load and frequency compensation capacitor is proposed. Adopting the RLC network load and the frequency compensation capacitor, the gain and phase imbalances of the output can be improved and the wideband response can be achieved, respectively. Moreover, this architecture can not only offer high transfer power gain, but also adopts the tuning current source to overcome the power imbalance caused by process variation. An example with a differential phase condition (180deg) has been designed and fabricated. Based on our measured results, in the frequency range from 3.5 to 6 GHz, the phase error is less than 7deg and the power imbalance is less than 1.4 dB. For wireless local area network 802.11a applications in the frequency range from 5.15 to 5.35 GHz, the phase error is less than 0.6deg, and the power imbalances are less than 0.27 dB, respectively. In addition, the transfer power gain is 9.66 dB under the power consumption of 15 mW and 1-V supply voltage. This architecture is different from the passive PPS circuit, and it has the advantages of no conversion loss and a small chip area with 0.8 mm times 0.7 mm. Compared with the conventional active PPSs, such as using the GaAs and BiCMOS process, this architecture implemented by the TSMC 0.18-mum CMOS process is competitive in cost and possesses the characteristics of low voltage and low power, and it is more easily integrated and suitable for system-on-a-chip applications.

Improvement in the Linearity of a LINC Transmitter using Genetic Algorithms

This paper proposes an automatically-adjusted linearization method based on the well-known linearization technique LINC (Linear amplification using Nonlinear Components) applied to the base station transmitter. A correction method of the gain and phase imbalances between both amplifying branches in a LINC transmitter is proposed to reduce the adjacent channel interference. A simple architecture is designed to compensate the unmatching between both branches being the adjusting coefficients calculated by means of a genetic algorithm. Several nonidealities are included in the analysis to deal with a realistic model, such as quadrature modulator imbalances, reconstruction filters and quantization error.

Spurious Signal Rejection using Real-Time Imbalance Compensation in Direct Conversion Transmitter

Using the real time compensation architecture for the gain and phase imbalance, a novel method for the spurious signal rejection of a direct conversion transmitter is presented in this paper. By deriving the gain- and phase-based functions from spurious signals with the channel imbalance information, the gain and phase imbalance is determined independently and simultaneously. The spurious signal can be effectively reduced by the compensation of the estimated I/Q-channel imbalance.

A2×1LINC Transceiver for Enhanced Power Transmission in Wireless Systems

A2×1LINC transceiver based on linear amplification using nonlinear components (LINC) architecture for wireless systems applications is proposed. The layout of the new architecture is presented and the simulation results show that the overall power efficiency of this architecture is superior by more than 300% when compared with that of a regular LINC amplifier. Also the adjacent channel power ratio (ACPR) is lowered to−64.2dBc, compared to−26.1dBc for regular LINC, which improves the system immunity against complex gain imbalances between LINC branches.

Matching requirements in LINC transmitters for OFDM signals

This paper presents a complete analysis of the effect of mismatches in linear amplification with nonlinear components transmitters for orthogonal frequency-division multiplexing modulated signals. Gain and phase imbalances between the two amplification paths can severely degrade the linearity performance introducing both out-of-band spectral regrowth and in-band distortion. Analytical expressions are derived to readily evaluate the contribution of mismatches to the adjacent-channel power ratio and error vector magnitude of the transmitter. A direct evaluation of the matching requirements can thus be obtained from the linearity specifications, without the need of time-consuming simulations.

Dual-band sub-harmonic quadrature mixer using composite right∕left-handed transmission lines

A dual-band (DB) sub-harmonic quadrature mixer using composite right/left-handed (CRLH) transmission lines (TL) is presented. The CRLH-TLs are used to provide dual-bandwidth operation in the Wilkinson power dividers (WPDs), the ±45° delay line for in-phase/quadrature generation, and the sub-harmonically pumped mixers. Theory and implementation of the RF/LO DB-WPDs, the dual-passband dual-stopband (DPDS) shunt terminations, and the DB sub-harmonically pumped mixers (SHPMs) are presented. These DB microwave components for the DB quadrature mixer are detailed in individual sections with both simulated and measured performances. The DB-WPDs exhibit S21 and S31 larger than −3.95 dB, return losses larger than 12 dB, isolations larger than 16 dB, phase imbalance less than 2.15°, and gain imbalance less than 0.25 dB at each passband. The DPDS terminations demonstrate insertion loss larger than 16 dB at stopbands and less than 2.3 dB at passbands. The DB-SHPM shows 10 dB and 11.7 dB conversion loss in low- and high-frequency mixing schemes with good linearity. Local oscillator (LO) to radio frequency (RF) isolation larger than 30 dB is also measured in both frequency mixing schemes. The measured results of the DB quadrature mixer display output amplitude balance, orthogonal characteristic, and LO to RF isolation larger than 45 dB.

An Adaptive Digital Method of Imbalances Cancellation in LINC Transmitters

The linear amplification using nonlinear components (LINC) technique is a well-known power amplifier linearization method to reduce adjacent channel interference in a nonconstant envelope modulation system. Its major drawback is the inherent sensitivity to gain and phase imbalances between the two amplifier branches. In this paper, a novel full-digital base band method is described which corrects any gain and phase imbalances in LINC transmitters mainly due to the unmatching of the two amplifier paths. Amplifiers are characterized by a level-dependent complex gain using a memoryless model. The method uses adaptive signal processing techniques to obtain the optimal complex coefficient to adjust gain and phase imbalances. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator imbalances and loop delay. A computer simulation has been carried out to verify the method functionality.

Nonlinear Distortion Cancellation Using LINC Transmitters in OFDM Systems

The LInear amplification using Nonlinear Components (LINC) technique is a well-known power amplifier linearization method to reduce out-of-band interferences in a nonconstant envelope modulation system, such as Digital Video Broadcasting (DVB) system, which is based on a very sensitive to nonlinear distortions OFDM modulation scheme. The major drawback of LINC transmitters is the inherited sensitivity to gain and phase imbalances between the two amplifier branches. In this paper, a novel full-digital base band method, which corrects any gain and phase imbalances in LINC transmitters mainly due to the un-matching of the two amplifier paths, is described. Amplifiers are characterized by a level-dependent complex gain using a memoryless model. The method uses adaptive signal processing techniques to obtain the optimal complex coefficients to correct gain and phase imbalances. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator impairments. A computer simulation has been carried out to verify method functionality.

Efficient Compensation for Frequency-Dependent Errors in Analog Reconstruction Filters Used in IQ Modulators

In a direct-conversion transmitter system, the nonideal transfer characteristics of practical analog subsystems can have significant adverse effects on the performance of the transmitter system. While a significant body of research exists on correcting static errors (including gain imbalance, phase errors, and DC offsets) in the analog subsystems, relatively little attention has been paid to the impact of nonideal frequency-dependent characteristics in the analog reconstruction filters that are employed in direct-conversion structures. This paper presents a new computationally efficient and numerically robust method for automatic digital compensation for nonideal frequency-dependent characteristics in the signal reconstruction filters of a quadrature (IQ) modulator structure. The new compensation technique is used in conjunction with existing compensation approaches that compensate for static errors.

A Joint Scheme of AGC and Gain/Phase Mismatch Compensation for QPSK DCR

This paper presents a simple gain/phase blind compensation algorithm with an automatic gain control (AGC) function for the adoption of the AGC function and compensation for gain/phase imbalances in quadrature phase shift keying (QPSK) direct conversion receivers (DCRs). The AGC function is interactively operated with the compensation algorithm for gain/phase imbalances. By detecting the gain sum and difference values between the I-channel and Q-channel, the combined AGC and gain imbalance compensation algorithm provides a simpler DCR architecture.

Directional frequency and recording (DIFAR) sensors in seafloor recorders to locate calling bowhead whales during their fall migration.

Bowhead whales, Balaena mysticetus, migrate west during fall approximately 10-75 km off the north coast of Alaska, passing the petroleum developments around Prudhoe Bay. Oil production operations on an artificial island 5 km offshore create sounds heard by some whales. As part of an effort to assess whether migrating whales deflect farther offshore at times with high industrial noise, an acoustical approach was selected for localizing calling whales. The technique incorporated DIFAR (directional frequency and recording) sonobuoy techniques. An array of 11 DASARs (directional autonomous seafloor acoustic recorders) was built and installed with unit-to-unit separation of 5 km. When two or more DASARs detected the same call, the whale location was determined from the bearing intersections. This article describes the acoustic methods used to determine the locations of the calling bowhead whales and shows the types and precision of the data acquired. Calibration transmissions at GPS-measured times and locations provided measures of the individual DASAR clock drift and directional orientation. The standard error of the bearing measurements at distances of 3-4 km was approximately 1.35 degrees after corrections for gain imbalance in the two directional sensors. During 23 days in 2002, 10,587 bowhead calls were detected and 8383 were localized.

Arbitrary Dual-Band Components Using Composite Right/Left-Handed Transmission Lines

Arbitrary dual-band microstrip components using composite right/left-handed (CRLH) transmission lines (TLs) are presented. Theory, synthesis procedure, and implementation of the dual-band quarter-wave (/spl lambda//4) CRLH TL are presented. Arbitrary dual-band operation is achieved by the frequency offset and the phase slope of the CRLH TL. The frequency ratio of the two operating frequencies can be a noninteger. The dual-band /spl lambda//4 open/short-circuit stub, dual-band branch-line coupler (BLC), and dual-band rat-race coupler (RRC) are also demonstrated. The performances of these dual-band components are demonstrated by both simulated and measured results. Insertion loss is larger than 23 dB for the shunt /spl lambda//4 CRLH TL open-circuit stub and less than 0.25 dB for the shunt /spl lambda//4 CRLH TL short-circuit stub at each passband. The dual-band BLC exhibits S/sub 21/ and S/sub 31/ larger than -4.034 dB, return losses larger than 17 dB, isolations larger than 13 dB, phase differences 90/spl deg//spl plusmn/1.5/spl deg/, and gain imbalance less than 0.5 dB at each passband. The dual-band RRC exhibits S/sub 21/ and S/sub 31/ larger than -4.126 dB, return losses larger than 12 dB, isolations larger than 30 dB, phase difference 180/spl deg//spl plusmn/4/spl deg/, and gain imbalance less than 0.2 dB at each passband.

ABSOLUTE CALIBRATION OF THE ERS-2 SCATTEROMETER IN GYRO-LESS MODE USING TRANSPONDERS

The scatterometer on-board ERS-2, earth-observation satellite developed by the European Space Agency, is an active real aperture radar instrument designed to measure the backscatter coefficient 0 from the earth. Its main utility is to measure physical parameters such as wind speeds and directions over the sea surface. Due to malfunctions of the on-board gyroscopes and even though a new attitude and orbit control system is used, the yaw-orientation of the spacecraft still exhibits random variations from the nominal attitude. This unpredictable attitude requires re-developing the calibration chain of the scatterometer instrument. Distributed targets, such as the rain forest, are used to perform a relative calibration while transponders situated at known locations in Spain permit an absolute calibration of the instrument. The scope is to expose the obtained results and the improvements brought by the new chain regarding the absolute calibration. An analysis of the received echo with a sub-pixel resolution (better than the nominal resolution) allows getting accurate transponder localization. The localization error is used to determine, among other quantities, the antenna mounting angles errors. Since the signal emitted by the transponders is calibrated, radiometric calibration is also possible, including determination of a large set of parameters such as the absolute gain of each antenna. The raw data quality (such as DC offsets, gain imbalance, phase imbalance) and the spatial resolution are also computed

Comparison of EDFA Setups using either Adaptive Equalization Filters or Fixed gain-flattening Filters with Respect to Noise Figure

Residual gain variations of erbium-doped fiber amplifiers (EDFAs) based on passive filtering techniques can accumulate over the entire transmission length and impose limitations on the link length. To overcome this problem, adaptive equalization filters have been developed that can rectify gain imbalances within each amplifier or at specific locations within the link. It is shown that such filters can also help to improve the noise figures provided by standard amplifier setups significantly. However, the investigation also reveals that amplifiers using a reconfiguration stage that can be inserted into or dropped out of the optical path can provide similar noise performance, although their realization is much easier and less cost intensive.

Coherent combining of two Nd:YAG lasers in a Vernier-Michelson-type cavity

The coherent combining of two Nd:YAG lasers using a Vernier–Michelson-type cavity has been demonstrated. The spectral behaviour and the energetic performance are reported. We firstly show that the combining efficiency is not strongly spoilt by the gain imbalance between the two amplifying media, and secondly, that despite the interferometric nature of the cavity, the Vernier–Michelson laser can withstand environmental perturbations without alteration in output power.

Assessment of performance limitations of Pon retrodirective arrays

We examine the behavioral characteristics of Pon type heterodyne retrodirective arrays (RDAs) (see Pon, C.Y., IEEE Trans. Antenna Propagat., vol.12, p.176-80, 1966) and provide a simple, yet comprehensive, modeling equation that allows the retransmission response of the RDA to be determined. Using this modeling philosophy, the optimum array size required for a prespecified beam pointing error is determined. Then, deleterious effects, such as mixer-leakage, phase-conjugate circuit gain imbalance and cable phase error, that occur due to the presence of real components, are quantified experimentally for a four-element RDA. These are then correlated with theory. Specific recommendations on the permissible tolerances allowable for these parameters are given in order to assist design specification adherence. In addition, it is shown in theory, and confirmed by measurement, how radiation element aberration due to diffraction and mutual coupling can be used to enhance the azimuthal tracking response of the array. This paper allows the first comprehensive, practical, and theoretical appraisal of the design limitations that exist for this type of array. The insights provided by this paper should be of value to practicing antenna engineers.

EDFA-based DWDM lightwave transmission systems with end-to-end power and SNR equalization

An approximate analysis is presented which can be used to predict the performance of power and signal-to-noise ratio (SNR) equalization schemes when applied to dense wavelength-division multiplexing (DWDM) lightwave systems employing erbium-doped fiber amplifier (EDFA) cascades. Expressions are provided which relate the maximum number of amplifiers, EDFA gain imbalance, bit rate (R/sub b/), transmitter power, receiver dynamic range and number of channels. The relative advantages of these two equalization strategies are quantified by comparing the maximum number of amplifiers allowed by each scheme. It is shown that, while SNR equalization represents, on balance, the more desirable equalization strategy for future EDFA-based DWDM lightwave transmission systems, under certain conditions power equalization may be a better choice. When employing an APD receiver, for instance, power equalization can support 1.9 times more amplifiers than SNR equalization. However, when employing the more conventional preamplified PIN/FET receiver, SNR equalization can support 1.7 times more amplifiers than power equalization.

Polarization insensitive gain medium with hybrid strained quantum well

A polarization insensitive gain medium for optical amplifiers has been fabricated. The active layer is a structure with alternate tensile and compressive strain quantum wells. The waveguide is made into a taper with angled facets. In the experiment we found that the structure can suppress the lasing and decrease the polarization sensitivity. The gain imbalance between transverse electric and transverse magnetic gains is small, and 0.1 dB is obtained at a driving current of 100 mA . The full-width at half-maximum of amplified spontaneous emission is 40 nm within large current.

Calibration scheme for LINC transmitter

A simple calibration scheme for correction of the path imbalance in a LINC transmitter is presented. By properly exchanging two LINC vector components and controlling a downconversion loop. The gain and phase imbalance are characterised by the baseband DSP/SCS. The error effects of the imbalance are compensated by introducing a pre-distortion term. Simulation results demonstrate that this scheme is sufficient to suppress the out-of-band spectrum for wireless communications.

Gain/phase imbalance-minimization techniques for LINC transmitters

Two simple calibration schemes for the correction of the path imbalance in a linear amplification with nonlinear components (LINC) transmitter have been demonstrated. In the foreground algorithm, a baseband digital signal processor (DSP) evaluates the gain and phase imbalance with a set of calibration signals, while in the background algorithm, the imbalance is characterized by exchanging the two LINC vector components. In both cases, the compensation of the path imbalance is accomplished within the DSP by introducing a predistortion term. A prototype LINC system has been tested for CDMA IS-95 baseband input, and -38 and -35-dBc adjacent channel interference were achieved for the foreground and background schemes, respectively. The quadrature errors of the in-phase/quadrature modulators set a limit on the overall performance of both algorithms.