This paper discusses the improvement in the third-order intermodulation product (IM3) performance obtainable from RF and microwave amplifiers by two alternative injection techniques. The first is the addition to the amplifier input of the second harmonics of the input spectrum and the second is the addition to the amplifier input of the difference frequencies between the spectral components of the input signal. Both techniques are considered in theory, by simulation and in practice. Both techniques give useful improvements in two-tone IM3 performance. The second harmonic technique reduced the IM3 level by 43 dB in an amplifier at 835 MHz. The difference-frequency technique gave a reduction of 48 dB in an amplifier at 880 MHz. The difference-frequency technique also gives a greater improvement for complex spectra signals.

/pdf/improvement-of-third-order-intermodulation-product-of-rf-and-2k3az1c7na.pdf

Improvement of third-order intermodulation product of RF and microwave amplifiers by injection

Since DC-offsets can have a large, negative impact on the performance of direct-conversion receivers, it is important to determine the offset performance of a given design. This article discusses one technique that can be used to characterize and measure dc-offsets in DCR circuit applications. DC-offsets are a primary concern in the design of DCRs and must be characterized in determining the performance of a particular receiver design. By measuring the dc level at the output of a DCR front-end in separate steps, the source of the offsets - device mismatches, LO self-mixing, and second order nonlinearities - can be resolved.

http://venividiwiki.ee.virginia.edu/mediawiki/images/9/93/DCR_Raman.pdf

DC offsets in direct-conversion receivers: characterization and implications

In this paper, an extensive study on the intermodulation distortion and the linearity of gate-material-engineered cylindrical-gate MOSFET (GME CGT MOSFET) has been done, and the influence of technology variations such as channel length and gate material workfunction variations is explored using an ATLAS 3-D device simulator. The simulation results reveal that the GME CGT MOSFET design displays a significant enhancement in the device's linearity and intermodulation distortion performance in terms of the figure-of-merit metrics VIP2, VIP3, IIP3, and IMD3 and the higher order transconductance coefficients gm1, gm2, and gm3. The results are, thus, useful for optimizing the device bias point for RFIC design with higher efficiency and better linearity performance.

An Investigation of Linearity Performance and Intermodulation Distortion of GME CGT MOSFET for RFIC Design

This paper presents a highly linear differential cascode CMOS power amplifier (PA) with gate bias circuits in Common Source (CS) and Common Gate (CG) amplifiers. The proposed Class-D bias circuit at the gate of a CS amplifier injects a reshaped envelope signal only when the envelope signal is above a certain threshold voltage. This improves the linearity of the PA without significantly degrading the efficiency in a high-power region. In addition, the proposed bias circuit at the gate of a CG amplifier controls the second-order nonlinear components to improve the linearity and to reduce the sideband (IMD or ACLR) asymmetry, simultaneously. A single-stage PA including the bias circuits was fabricated using a 0.18-μ m CMOS process, with an integrated passive device (IPD) transmission line transformer (TLT). With a 3.5 V supply, the measurements show that 26.8 dBm with 43.3% PAE at -37 dBc ACLR (5 MHz offset) and 27.8 dBm with 45.8% PAE at -33 dBc ACLR (5 MHz offset) at 1.85 GHz under 3GPP WCDMA test without digital pre-distortions.

Integrated Bias Circuits of RF CMOS Cascode Power Amplifier for Linearity Enhancement

This article reviews the main parts of a software-defined radio (SDR) to emphasize several possible implementations of both receivers and transmitters. We describe solutions for testing and characterizing these types of devices. SDRs typically operate in both the analog and the digital domains, thus mixed-domain instrumentation is necessary to carry out testing. We first give a short overview of several architectures for SDR receiver front ends. Then, several possible architectures for transmitter front ends are described. We discuss methods that can be used to improve amplifier efficiency. Instrumentation currently available in the commercial market that allows the characterization of such types of transceivers is presented.

Designing and Testing Software-Defined Radios

Applications of direct frequency-conversion techniques have been rapidly getting attention of radio designers worldwide. This paper focuses on bringing out key implementation challenges of direct conversion receivers and transmitters targeted for different second- and third-generation mobile phone standards like global system for mobile communication, code division multiple access (cdmaOne and CDMA 2000), and wide-band code division multiple access. Techniques and tradeoffs to arrive at optimal implementation are highlighted. Some of the commercially available application-specific integrated circuits that are based on direct conversion architecture and their salient features are summarized.

Direct conversion radio for digital mobile phones-design issues, status, and trends

This paper describes a novel technique for reducing the third order intermodulation (IMD) product and ACPR levels in HBT power amplifiers. This technique is based on the dynamic control of the injection/feedback of the second harmonic frequency signal to the amplifier. For a cellular frequency HBT MMIC power amplifier, a reduction of 44 dB in the 3rd order IMD level is measured at 28 dBm output power. By controlling the phase and amplitude of the injected/fedback second harmonic, a total rejection of IMD products over a wide dynamic range of input power is achieved without any change in the fundamental signal levels. The ACPR for CDMA system (IS-98 standard) over a 30 kHz bandwidth with /spl plusmn/900 KHz offset shows a 6 dB improvement. No degradation in the CDMA signal quality factor (/spl rho/) and PAE (40%) are observed. To the best of our knowledge this is the first application of this technique to HBT power amplifiers.

IMD elimination and CPR improvement for an 800 MHz HBT MMIC power amplifier

This presentation will give an overview of the design issues related to the implementation of direct conversion receiver for mobile phones, provide the current status and discuss future trends.

F. Ali

Papers

Improvement of third-order intermodulation product of RF and microwave amplifiers by injection

Direct conversion radio for digital mobile phones-design issues, status, and trends

IMD elimination and CPR improvement for an 800 MHz HBT MMIC power amplifier

Direct conversion receiver design for mobile phone systems - challenges, status and trends

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