Low Intermodulation Distortion Research Articles

Comprehensive characterization of a high‐performance double heterojunction InGaAs pHEMT for linear power‐efficient amplifiers applications

AbstractThis article centers its attention on the phenomenon of electrostatics, linearity, analogue, and RF performance of a 0.5 μm × (2 × 100) μm double heterojunction AlGaAs/InGaAs/GaAs pHEMT using on‐wafer DC and RF measurements up to 50 GHz. With a high ION/IOFF ratio (1.21 × 107) and low subthreshold slope (72.7 mV/dec), a flat and high transconductance over a wide range of Vgs has been achieved for the tested device. Furthermore, the input intercept and higher‐order voltage intercept point both attained large values with low intermodulation and harmonic distortion. Regarding RF parameters, the intrinsic gain has been achieved up to 28 dB. The GBW up to 750 GHz was attained, with the highest fT and fmax values being 24.5 GHz and 99.3 GHz, respectively. Since the device has very low intrinsic capacitance, parameters like TFP, GFP, and GTFP also showed excellent results. The high intrinsic gain and TGF indicate ample potential of the device for use as an amplifier. Investigating the parameters reveals the device to have very good linearity and amplifying capability.

Linearity improvement in graded channel AlGaN/GaN HEMTs for high-speed applications

AlGaN HEMTs are popular devices for high-frequency applications. At higher frequencies, nonlinearity effects are major concerns and need serious attention. In this work, we have attempted to improve the linearity performance of graded channel Al x Ga1−x N/GaN HEMTs in comparison with abrupt channel GaN HEMTs through Technology Computer Aided (TCAD) simulation. In graded channel HEMTs, linearly grading of Al composition in the AlGaN layer, reduces the local carrier densities and provides improvement in the carrier saturation velocity. This provides an avenue to improve the overall linearity performance. A complete set of figures of merits (FOMs) such as and for both devices are presented. The simulation results have been calibrated with reported experimental results available in the literature. The graded devices are observed to have better transconductance (g m ) and drain current for gate voltages greater than −2 V. The drop in g m is reduced by nearly 50% at the higher gate-to-source voltages. Moreover, the RF figure of merits such as the current gain cutoff frequency (f T) and a maximum frequency of oscillation (f max) have been calculated for both devices. Due to the graded channel f T increases by 20% and f max becomes twice which makes it a better choice for high-voltage and high-power applications. The impact of interface trap and leakage current performance on the graded channel device are also reported. The cutoff frequency reduces by 25% with an increase in trap charge concentration from 9e17 cm−2 to 1e19 cm−2. Also, it has been found that the graded channel device shows better linearity and lower intermodulation distortion in comparison to the abrupt device which has been calculated from the linearity parameters. The high gate leakage current in the case of the graded channel device can be reduced by adding a thin GaN cap layer on the AlGaN channel which can be a future prospect of improving the performance of the graded GaN device.

Design and Analysis of a Hybrid-Type RF MEMS Phase Detector in X-Band.

In this paper, we have designed, analyzed, and characterized a hybrid-type MEMS device for X-band phase shift measurement. The signal related to a phase shift of the inputs is fractionally in-line coupled by a MEMS beam and delivered to a thermoelectric power sensor, where the phase is ultimately converted into DC voltage output. With the hybrid of the MEMS beam and the thermoelectric power sensor, both in-line detection process and phase-DC voltage conversion is reserved, which is a benefit for large power capacity, good linearity property, and high-level integration density. In order to get a deep insight into the physical mechanisms involved in the phase detection process, a comprehensive analysis model is presented. The beam is modeled as a precise RLC circuit component, where the capacitance is related to the input power. The fabrication is compatible with GaAs monolithic microwave integrated circuit (MMIC) technology. Experimental results show that return loss is smaller than −11.3 dB and isolation is better than −9.3 dB over X-band. Phase shift detection from 0 to 180 degrees is verified for a large power range of 200–1600 mW (23–32 dBm). The perfect linearity property of the phase-detection sensitivity is demonstrated in the same power range. Low intermodulation distortion is also confirmed through measurement. It is revealed from the comparison between this work and other published results in the literature that this presented hybrid-type structure shows superiorities in both power handling ability and phase-detection linearity. It can be adopted in medium power signal applications with a high level of integration.

Design of Wide-band Power Amplifier based on Power Combiner Technique with Low Intermodulation Distortion

RF power amplifiers are one of challenging blocks in designing radio frequency transceivers, this is due to non-linearity behavior of power amplifiers that leads to inter-modulation distortion. This paper presents the design of wide-band power amplifier which combined with parallel coupled line band pass filter at the input and output of power amplifier to allow the only required frequency band to pass through the power amplifier. Class-A topology and ATF-511P8 transistor are used in this design. Advanced Design System software used as a simulation tool to simulate the designed wide-band power amplifier. The simulation results showed an input return loss (S11) which less than -10dB, and gain (S21) is higher than 10 dB over the entire frequency band and considers as flat as well. The designed amplifier is stable over the bandwidth (K>1). Inter-modulation distortion is -56.919dBc which is less than -50dBc with 10dBm input power. The designed amplifier can be used for the microwave applications which include weather radar, satellite communication, wireless networking, mobile, and TV.

A 2.65 W high-fidelity filterless class D audio amplifier using multiple loop filters

The design of a 2.65 W, high-fidelity, filterless Class D audio amplifier in a standard 0.5 μm CMOS technology is proposed in this paper, where an architecture with multiple loop filters is utilized. This structure attenuates residual clock signals around the loop allowing very low total harmonic distortion (THD) and intermodulation distortion to be achieved in conjunction with high power supply rejection ratio (PSRR). The active area of this circuit is about 1.5 × 1.5 mm2. The THD + N is <0.03 % at 1 kHz input frequency and 100 mW output power. The PSRR is ?80 dB at 217 Hz and maximum output power at 10 % THD is 2.658 W. A Figure of merit is defined to estimate the excellent performance which can meet the demands of portable communication devices greatly.

Highly Linear Radio-Over-Fiber System Incorporating a Single-Drive Dual-Parallel Mach–Zehnder Modulator

We propose a highly linear radio-over-fiber system with low intermodulation distortion (IMD) using a single-drive dual-parallel Mach-Zehnder modulator (SD-DPMZM). The optical carrier is modulated in one of the two parallel modulators, while remaining unmodulated in the other one. There exists optimal working points for SD-DPMZM that makes its two kinds of origins of third-order IMD (IMD3) have opposite phase and equal intensity, and cancel each other; hence the output IMD3 is suppressed dramatically. Experimental results show that the proposed scheme can achieve a spurious-free dynamic range of up to 122.9 dB · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> , which is in agreement with the theoretical analysis. It is about 20 dB more than a conventional MZM. The error vector magnitude of the proposed scheme, for a 16-QAM 10-MSym/s signal centered at 4 GHz, is 1.94%.

Distortion Compensation for Thermal Memory Effect on InGaP/GaAs HBT Amplifier by Inserting RC-Ladder Circuit in Base Bias Circuit

An inter-modulation distortion (IMD) compensation method for thermal memory effect using a multistage RC-ladder circuit has been proposed. The IMD caused by the thermal memory effect on an InGaP/GaAs HBT amplifier was compensated for by inserting a multistage RC-ladder circuit in the base bias circuit of the amplifier. Since heat flux owing to self-heating in the transistor can be approximated with a multistage thermal RC-ladder circuit, the canceling of IMD by an additional electrical memory effect generated from the RC-ladder circuit is predicted. The memory effects cause asymmetrical characteristics between upper and lower IMD. The IMD caused by the memory effects is expressed as a vector sum of each origin. By adjusting an electrical reactance characteristic for sub-harmonics affected by the thermal memory effect in the amplifier circuit, the asymmetric characteristic is symmetrized. The parameters of the RC-ladder circuit were estimated so that the adjusted electrical reactance characteristic is reproduced in simulation. A fabricated InGaP/GaAs HBT amplifier with the thermal memory effect compensation circuit exhibited a symmetrized and suppressed IMD characteristics.

Microelectrical Mechanical Systems Switch for Designing Multi-Band Antenna

Problem statement: In this study Microelectrical Mechanical System (MEMS) switches were proposed to design a reconfigurable/multi-band antenna to replaced PIN diode switches or semiconductor switches due to lower insertion losses, good isolation, much lower intermodulation distortion, and lower power consumption. The antenna is able to operate at very high frequencies. Approach: A reconfigurable antenna that is capable to operate at several frequencies was proposed by introducing two adjacent patches along with main radiating patch and two MEMS switches. Parametric analysis of the size of the wing patches was done for finding optimum size. A comparative study was done for Alumina, SiN, GaAs and Teflon as MEMS bridge materials for finding better results in terms of return loss and number of bands. The design was performed by using 3D electromagnetic simulator HFSS considering ideal MEMS switches. Results: It was found that SiN as MEMS bridge material makes the antenna to operate at 16.76, 23.56 and 27.7 GHz in the &#34OFF&#34 states and operate at 20.9 and 21.91 GHz in the &#34ON&#34 states of MEMS switches. Conclusion/Recommendations: MEMS cantilever beam material played an important role for providing antenna to operate at multi-band frequencies. The proposed multiband/reconfigurable antenna can be implemented with easy fabrication process steps by the Sandwich method of fabrication.

Intermodulation Distortion in Epitaxial Y-Ba-Cu-O Thick Films and Multilayers

We report intermodulation distortion (IMD) in high-quality epitaxial YBa2Cu3O7-delta (YBCO) thick films and multilayers prepared by pulsed-laser deposition (PLD) using multiple targets. Two sets of films were prepared: single-layer and multilayer YBCO films in which a 20-nm-thick CeO2 inter layer is inserted between every 100-nm-thick YBCO layer. With increasing YBCO thickness from 200 nm to 1200 nm, single-layer films exhibited improvement of IMD, whereas multilayer films showed degradation of IMD. Similarly, YBCO crystalline quality in single-layer films was improved with increasing the thickness, while that in multi-layers films degraded. These results suggest that there is a strong correlation between crystalline quality and IMD for YBCO films. The comparison of experimental data with the theory of IMD suggests that improving crystalline quality is essential for YBCO films with thickness greater than 1 mum to achieve an intrinsic nonlinear behavior. PLD using multiple targets is a very useful method to grow thick YBCO films with high crystalline quality and low IMD.

A Single–Chip 10-Band WCDMA/HSDPA 4-Band GSM/EDGE SAW-less CMOS Receiver With DigRF 3G Interface and ${+}$90 dBm IIP2

This paper describes the design and performance of a 90 nm CMOS SAW-less receiver with DigRF interface that supports 10 WCDMA bands (I, II, III, IV, V, VI, VIII, IX, X, XI) and 4 GSM bands (GSM850, EGSM900, DCS1800, PCS1900). The receiver is part of a single-chip SAW-less transceiver reference platform IC for mass-market smartphones, which has been designed to meet Category 10 HSDPA (High Speed Downlink Packet Access) requirements. The novel receiver core consists of a single-stage transconductance amplifier (TCA) with large gain control range, a current commutating passive mixer enhanced for automatic on chip IIP2 calibration with 25% duty-cycle LO injection and threshold adjust, and current-input complex Direct Coupled Filter (DCF). The low noise TCAs are designed without inductive loads to save area. A self-contained on chip automatic IIP2 calibration system with algorithm routine, implemented in firmware, is used to optimize IIP2 performance. This topology eliminates the external LNA, inter-stage SAW filter and transimpedance amplifier (TZA) in conventional WCDMA designs and results in current drain and die area savings as well as improved noise. The 25% duty-cycle LO injection, with threshold adjustment, into a current driven passive double-balanced mixer results in 3 dB additional gain, lower noise figure and lower intermodulation distortion. Large signal blocking and 1/f noise performance are improved significantly by eliminating the 0 and 180deg LO signal crossover at the mixer. The full receiver achieves 2.2 dB/2.39 dB simplex/duplex NF (with - 24.5 dBm TX leakage), > 90 dBm complex two-tone IIP2, 60 dB gain and - 1/+ 5 dBm half/full-duplex image IIP3. The receiver core consumes only 15.1 mA from a 1.5 V supply.

480-Mbps, Bi-Directional, Ultra-Wideband Radio-Over-Fiber Transmission Using a 1308/1564-nm Reflective Electro-Absorption Transducer and Commercially Available VCSELs

We describe 480 Mbps, bi-directional ultra-wideband (UWB) radio signal transmission over 1 km of single-mode optical fiber. Key components are a highly linear, reflective electro absorption transducer (EAT) and commercially available 1308-nm and 1564-nm VCSELs with 4.8-GHz bandwidth. Detailed EAT and 1308-nm VCSEL distortion analyses and measurements are presented highlighting the low intermodulation and harmonic distortion necessary for typical -18-dB wireless channel error vector magnitudes (EVMs). Direct VCSEL modulation with Wimedia supported band group 1 (3.1-4.8 GHz) MB-OFDM UWB signals was modelled with VPItransmissionMaker, suggesting a minimum EVM of -18.733 dB at 0.4502 OMI. This was confirmed by 480 Mbps upstream and downstream EVM measurements over fiber of -21.4 dB or better. Fully functional, half-duplex, bi-directional data transfer was achieved with interlocked RF switches.

Power Supply Noise in Analog Audio Class D Amplifiers

A potential drawback of class D amplifiers (CDAs) is their relatively poor tolerance to power supply noise. It has been recently established by means of a linear model that the manifested nonlinearities due to the supply noise are the fundamental noise frequency component and second-order intermodulation components, qualified by the power supply rejection ratio (PSRR) and intermodulation distortion (IMD), respectively. In this paper, multidimensional Fourier series analysis is applied to open-loop, single-, and double-feedback pulsewidth modulation CDAs, and expressions for PSRR, IMD, and fold-back distortion (FBD) are derived. This analysis takes into account the nonlinear pulse modulation process (unaccounted for in the linear model), and all components of PSRR and IMD nonlinearities are hence modeled. It is shown that the first-harmonic PSRR and third-order IMD components, which are usually ignored in CDAs and linear amplifiers, are significant and that, under certain conditions, the third-order IMD components can be higher than the second-order IMD components. It is also shown that the loop gain should be high for high PSRR and low IMD. Furthermore, significant FBD can arise due to the intermodulation between the supply noise, the input signal, and the carrier, and interestingly, the FBD in closed-loop CDAs is more serious than that in open-loop CDAs. The analyses herein are verified by computer simulations and on the basis of measurements on a prototype CDA IC and on other hardware realizations.

5 GHz HTS power filters with TM-mode microstrip-disk resonators

For RF wireless applications, high-temperature superconducting (HTS) microwave power filters are desired to satisfy the requirements of higher power handling capability, lower intermodulation distortion (IMD), and dimensions that are more compact. In this report, we propose a 5 GHz HTS band bandpass filter (BPF) that has 2 dual-mode resonators using TM 11-mode microstrip-disk (MD) resonators and waveguide line for electromagnetic (EM) coupling between the MDs. The BPF sample with YBCO films on both sides of an MgO (1 0 0) substrate was fabricated, and their RF characteristics of the S parameters, the power, and 3rd IMD (IMD3) were examined. The filter sample exhibited an IMD3 value less than −70 dBc at 10 W input power, and was estimated the half volume of a conventional 4-pole MD BPF.

CATV/ROF transport systems based on −1 side mode injection-locked and optoelectronic feedback techniques

A directly modulated CATV/radio-on-fiber (ROF) transport system based on −1 side mode injection-locked and optoelectronic feedback techniques is proposed and demonstrated. Good performances of carrier-to-noise ratio (CNR), composite second-order (CSO) and composite triple beat (CTB) were obtained for the CATV band, as well as low third-order intermodulation distortion to carrier ratio (IMD3/C) and bit error rate (BER) values were achieved for the intelligence transport system (ITS) application. This demonstrated CATV/ROF transport system is a promising candidate for long-haul fiber transmission applications.

Intermodulation distortion measurements of MgB2 thin films grown by HPCVD

The two tone intermodulation distortion (IMD) arising in MgB2 thin films synthesized by hybrid physical-chemical vapour deposition (HPCVD) is studied in order to probe the influence of the two bands on the symmetry of the gap function. The measurements are carried out by using a dielectrically loaded copper cavity operating at 7 GHz. Microwave data on samples having critical temperatures above 41 K, very low resistivity values, and residual resistivity ratio larger than 10, are shown. The dependence of the nonlinear surface losses and of the third order intermodulation products on the power feeding the cavity and on the temperature is analyzed. At low power, IMD versus temperature data show the intrinsic s-wave behaviour expected for this compound

A vector intermodulation analyzer applied to behavioral modeling of nonlinear amplifiers with memory

A large signal vector intermodulation network analyzer with a dynamic range of 90 dB and phase resolution of better than 2/spl deg/ is reported. The analyzer is used in conjunction with a multislice behavioral model to characterize memory effects in three different RF power amplifiers: an MOSFET instrumentation amplifier, a multistage GaAs/silicon-based broadband microwave integrated-circuit amplifier, and an SiGe HBT monolithic-microwave integrated-circuit amplifier. The multislice behavioral model architecture builds on conventional single-tone AM-AM and AM-PM modeling extended to capture long-term memory effects that are characterized by asymmetric intermodulation distortion (IMD). Phase asymmetries of upper and lower IMD are captured. A systematic procedure for extracting the model is presented.

C-band GaAs FET power amplifiers with 70-W output power and 50% PAE for satellite communication use

This paper describes a successfully developed high-power and high-efficiency C-band GaAs FET amplifier for satellite communication systems. To realize high efficiency in a high-power amplifier, an HFET well-designed for high-power applications is developed, and precise design for an amplifier is carried out. The HFET employed achieves reduction in a gate leakage current while maintaining a high maximum drain current. For precise design of an amplifier, large-signal FET model parameters are extracted using pulsed I-V and S-parameter measurements. Based on this model, second harmonic impedances as well as fundamental impedances are determined for obtaining high efficiency and input- and output-matching circuits which are assembled in a compact package are designed to achieve a high-efficiency internally matched amplifier. As a result, the amplifier delivers a high saturated output power of 70 W and a high power-added efficiency of 51%. These characteristics are the record power performance in C-band in terms of simultaneous achievement of high power and high efficiency. A low third order intermodulation distortion of -35 dBc is also obtained at a drain voltage of 10 V.

Improving the linearity‐efficiency trade‐off in FET power amplifiers using large‐signal IMD sweet spots

AbstractIn this paper, a device‐level bias‐adaptation technique for improving the linearity‐efficiency trade‐off in Class‐B FET power amplifiers is introduced. The proposed approach uses the low‐current large‐signal intermodulation distortion sweet spot that appears below the VGS pinch‐off voltage as the bias point. A detailed characterization of the sweet‐spot evolution shows that a dynamic dual‐bias adjustment could guarantee, under strong input‐power level variations, low in‐band intermodulation distortion while the amplifier remains working around its highest efficiency value. The proposed technique is validated using an IS‐95 QPSK signal. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 327–331, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20132

Nonlinear response of Gb-Ba-Cu-O and Y-Ba-Cu-O microstrip resonators on sapphire

HF power-induced nonlinear effects, including the two-tone intermodulation distortion (IMD), were examined by using 2.3 GHz microstrip resonators prepared from double-sided YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) and GdBa/sub 2/Cu/sub 3/O/sub 7-x/ (GBCO) films on CeO/sub 2/ buffered sapphire. Both, the YBCO and the GBCO resonators exhibited similarly high performance with low IMD level. The third-order interception points varied linearly with temperature from P/sub TOI//spl ap/1500 W of the circulating power, P/sub circ/, at 4.2 K to P/sub TOI//spl ap/90 W at 77.4 K. The dependence of the IMD products on the P/sub circ//P/sub TOI/ ratio was found to be the same at all measurement temperatures. Similarly, the variation of the microwave surface resistance /spl Delta/R/sub S/ versus P/sub circ//P/sub TOI/ was found to be temperature-independent. The combination of these dependences provided a universal relation between the power of the IMD signals and /spl Delta/R/sub S/, which was exhibited by both YBCO and GBCO resonators in the entire examined temperature range.

Requirements for low intermodulation distortion in GaN-Al/sub x/Ga/sub 1-x/N high electron mobility transistors: a model assessment

A model analysis of the large-signal characteristics of GaN-Al/sub x/Ga/sub 1-x/N high-electron mobility transistors (HEMTs) with particular emphasis on intermodulation distortion (IMD) and the third-order intercept point. Since the nonlinearity depends critically on the carrier transport behavior, a Monte Carlo (MC) based numerical simulation scheme has been employed. The focus is to identify parameters and their interdependencies with a view of setting optimal limits for enhanced microwave performance. A case is made for increased mole fraction for the barrier layer, reducing the transit length, and introducing a thin AlN interfacial layer for suppressing real space transfer for enhancing the device performance. Finally, high-temperature predictions of the nonlinear behavior and IMD have been made, by carrying out the MC simulations at 600 K. In a process a favorable case is made for the GaN system as a potential candidate for microwave and RF applications at elevated temperatures.