Intermodulation Distortion Analysis of MESFET Amplifiers Using the Volterra Series Representation

Third-order intermodulation distortion generated in a MESFET amplifer is analyzed by means of the Volterra series representation. A transistor model is used which enables direct analytical determination of the nonlinear elements from small-signal measurements. The four nonlinearities considered are the gate capacitance, transconductance, drain feedback capacitance, and output conductance. Volterra transfer functions are derived for a simplified model and closed-form expressions for the third-order intermodulation ratio and intercept point are determined. The equations show the dependence of distortion on frequency, terminating impedances, and transistor parameters. Principal sources of distortion are identified and the influence of device parameters and network terminations is investigated. Experimental verification on specific MESFET amplifiers, with 2-mu m and 1-mu m gate devices, comparing predicted and measured intermodulation products for various load conditions is presented.     

Optimization of Third-Order Intermodulation Product and Output Power from an X-Band MESFET Amplifier Using Volterra Series Analysis

A third-order analysis for accurately predicting large-signal power and intermodulation distortion performance for GaAs MESFET amplifiers is presented. The analysis is carried out for both single- and two-tone input signals using the Volterra series representation and is based only on small-signal measurements. Simple expressions for the nonlinear power gain frequency response, the output power, the gain compression factor, and the third-order intermodulation (IM/sub 3/) power are presented. The major sources of gain compression and intermodulation distortion are identified. Based on the developed nonlinear analysis in conjunction with the device nonlinear model, a systematic procedure for designing a MESFET amplifier under large-signal conditions for optimum output power and IM/sub 3/ performance is proposed. The method utilizes out of band computed matching compensation through a nonlinear model of the amplifier. The accuracy of the device large-signal and IM/sub 3/ distortion characterization and the practicability of the proposed method are illustrated through comparison between measured and predicted results.     

AlGaAs/GaAs HBT linearity characteristics

Communication systems require linear power amplifiers with high efficiency and very low intermodulation distortion. AlGaAs/GaAs heterojunction bipolar transistors (HBT's) were found to have very low intermodulation distortion in power operation. Two-tone tests were carried out on both common-emitter (CE) and common-base (CB) power HBT's. At 7 GHz, the CE HBT showed -20 dBc IM₃ (third-order intermodulation ratio) and 12% power added efficiency (PAE) per tone at the 1 dB gain compression point; IM₃ dropped to -30 dBc at 1.5 dB output power backoff. The CE HBT has lower intermodulation distortion than CB HBT. Load pull data were collected to aid the understanding of the intermodulation. Parameters of the Gummel-Poon model (as used in SPICE) were derived for HBT's based on dc data and small-signal S parameters at various bias points. The accuracy and validity of the model were confirmed by comparison to experimental two-tone results. SPICE predicts that the emitter and base resistances linearize the HBT and reduce the third-order intermodulation distortion. The excellent third-order intermodulation performance of the CE HBT makes it a very attractive choice for linear power amplifiers     

An amplifier linearization method based on a quadrature balanced structure

A quadrature balanced structure is presented for linearizing amplifiers. It works by reducing the most annoying distortion component: the third-order intermodulation. This arrangement has some advantages over the negative feedback method, which is prone to oscillations. It also has advantages over predistortion and feedforward linearization methods, as it is simpler and needs no adjustments. Theoretically, third-order intermodulation products would be totally eliminated when using the proposed arrangement. In practice, it was observed that, even with nonperfectly balanced amplifiers, the third-order intermodulation level was reduced up to 17 dB. The fifth-order intermodulation components were not reduced.     

Spatial separation of the third-order intermodulation for amplifier linearization

A quadrature balanced structure is presented for linearizing amplifiers. It works by routing the most annoying distortion component (the third-order intermodulation) to a port, while routing the useful information signals to a distinct port. This arrangement is not prone to oscillations as the negative feedback method is. It also has advantages over predistortion and feedforward linearization methods, as it is simpler and needs no adjustments. Theoretically, third-order intermodulation products would be totally eliminated when using the proposed arrangement. In practice, it was observed that, even with non-perfectly balanced amplifiers, the third-order intermodulation level was reduced up to 17?dB. The fifth-order intermodulation components were not reduced.     

Fiber Optic Intermodulation Distortion

In analog frequency-division multiplexed fiber optic systems, laser nonlinearities transfer energy between the different carriers, resulting in intermodulation distortion and interference. A third-order polynomial without memory is used to model the nonlinearity. The FM frequency-division multiplexed (FM/FDM) signal consists of a set of FM carriers at frequencies.N_{omega 0}, whereN = L, L + 1, L +2, ... , M. The video distortion introduced by the nonlinearity is determined for various types of second- and third-order intermodulation terms. The intermodulation distortion frequency spectrum is determined for FM signals with assumed Gaussian spectra.     

An analog compensation method for asymmetric IMD characteristics of power amplifier

The modulation frequency affects the asymmetric intermodulation distortion (IMD) products of a RF power amplifier. This effect reduces IMD cancellation performance of power amplifiers in connection with predistortion linearization. A phase extraction method to determine phase difference between upper and lower third-order IMD products and a phase compensation circuit using an envelope injection technique is proposed. The experimental results demonstrate a significant improvement in the third-order IMD cancellation performance.     

Inter modulation distortion analysis of cascaded MESFET amplifiers using Volterra series representation

The third-order intermodulation distortion generated in a two-stage cascaded amplifier is derived analytically by means of the Volterra series expansion, for non-linear systems with memory. A unilateral transistor model is used, which takes into account the three major non-linearities, the gate capacitance, the trans-conductance and the output conductance, in each stage of the amplifier. The Volterra transfer functions are determined for this transistor model and closed-form expressions for the intermodulation distortion ratio are given, where the terms with a contribution less than 1% have been neglected. The equations identify the principal sources of the distortion in the amplifier circuit and the influence of the transistor parameters and load impedance is investigated. The analysis of the two-stage cascaded amplifier gives a new insight into the intermodulation distortion behaviour and is discussed in detail at the end of the paper. The results obtained here are compared with those received for single-stage amplifiers.     

Nonlinear and Intermodulation Characteristics of Millimeter-Wave IMPATT Amplifiers

An analysis and experimental results of intermodulation distortion characteristics of millimeter-wave IMPATT amplifiers are presented. Design considerations for linear IMPATT amplifiers and tradeoffs between the small-signal gain and intermodulation distortion are discussed.     

Magnetic-Feedback-Based Predistortion Method for Low-Noise Amplifier Linearization

A predistortion method for CMOS low-noise amplifiers (LNAs) to be used in broadband wireless applications is presented. The method is based on the nulling of the third-order intermodulation distortion of the main amplifier by a highly nonlinear predistortion branch. Maximum nonlinearity product cancellation is ensured by a transformer feedback method. The technique improves linearity in a wide range of input power without significant gain and noise figure (NF) degradation. Simulation results on a 1-V LNA indicate a 10.3-dB improvement in the third-order input intercept point with a degradation of only 1 and 0.44 dB in amplifier gain and NF, respectively. The design is based on a 0.13-mum CMOS technology     

FM Nonlinearity Due to Harmonic Distortion in the Carrier Path

The intermodulation noise in FM transmission caused by harmonic distortion in the carrier path is calculated by deriving the second- and third-order terms of the distorted signal. Explicit relations are given in terms of filter delays, harmonic levels, and modulation transfer parameters.     

Nonlinear models for the intermodulation analysis of FET mixers

An accurate, detailed analysis program has been developed for intermodulation distortion (IMD) simulation of FET mixers. This program is very efficient at calculating the IMD from multiple RF inputs. We have proposed a simplified nonlinear model for IMD analysis of FET gate mixers. The accuracy of the simplified model has been verified experimentally using two different MESFET mixers and one HEMT mixer at X band. All the tests show good agreement between measured results and the calculated results for second- and third-order IMD. The simplified model is based on modeling the derivative of the device transconductance by a sum of a Gaussian function and a linear function of the gate voltage. Drain bias dependence is ignored. The advantage of this model is that it can be used for both MESFET and HEMT mixers, and its fitting parameters can be easily determined from a nonlinear characterization of the devices at low frequencies     

Multiple FM/FDM Carriers Through Nonlinear Amplifiers

For long haul transmissions using frequency-division multiple-access methods, several frequency-modulated carriers are transmitted over a common communications channel consisting of saturating amplifiers operated near saturation to maximize the system power efficiency. One of the problems caused by saturating high power amplifiers is intermodulation distortion, which is the subject of this paper. A simple computation method is introduced which is potentially useful in calculating intermodulation distortion effects of FDM/FM equal power carriers. Based on the results of the study, new and simple empirical expressions for the amplitudes of the single third-order intermodulation products are then presented and compared to previous theoretical and experimental results.     

Two-Tone Intermodulation in Diode Mixers

This paper explores, experimentally and theoretically, the problem of minimizing second- and third-order intermodulation distortion in diode mixers. A numerical technique is presented which can be used to calulate internrodulation levels with unprecedented accuracy, and it is used to identify circuit and diode parameters which maximize dynamic range. It is shown that intermorhdation distortion is minimized by using low diode junction capacitance and series resistance, short-circuit embedding impedances, and high local-oscillator level. It is also shown that certain conditions which may optimize conversion loss, such as image enhancement, may severely exacerbate intermodulation.     

Circuit Model for Characterizing the Nearly Linear Behavior of Avalanche Diodes in Amplifier Circuits

A nonlinear circuit model for avalanche diodes is proposed. The model was derived by assuming that the bias dependence of the elements in a known small-signal equivalent-circuit model for existing diodes arises in a manner consistent with the theory of an idealized "Read-type" device. The model contains a nonlinear RL branch, a controlled source, and a linear depletion capacitance. The model is used in the nearly linear sense to predict intermodulation distortion (IMD) and gain compression in avalanche diode amplifiers. Computed results for amplifiers with existing diodes are shown to be in good agreement with experiment.     

Accurately modeling the drain to source current in recessed gateP-HEMT devices

In this work, a continuous nonlinear model for the I_ds current source in recessed gate pseudomorphic HEMT heterostructures is proposed. A careful characterization of the DC, pulsed, and small-signal nonlinear distortion behaviour of this predominant nonlinearity has been employed in order to extract the model parameters. Being able to reproduce the current-voltage (I-V) behaviour as well as the higher order derivatives of the transconductance and output conductance, the equation is valid for an accurate control of the critical nonlinear distortion phenomena in HEMT applications. Comparisons between measured and simulated results prove its validity under both static and dynamic conditions for either large- or small-signal operation     

Intermodulation distortion improvement by active compensation in impatt amplifiers

The letter discusses how the intermodulation distortion in impatt diode amplifiers can be improved significantly by active compensation. Theoretical evaluation based on a large-signal impatt diode model predicts considerable improvement in the intermodulation behaviour; in particular, the improvement in the third-order intercept point is found to be in excess of 12 dB.     

晶体管非线性失真分析

本文从器件物理和结构上提出双极型晶体管非线性失真模型。模型包含8个参量:(1)有效基区展宽效应;(2)发射极电流集边效应;(3)基区电导调制效应;(4)发射结电阻的非线性效应;(5)发射结电容的非线性效应;(6)集电结电容的非线性效应;(7)寄生电容的非线性效应;(8)电流放大系数和雪崩倍增效应与电压的非线性关系。利用Taylor级数展开分析各模型参数,并编制了计算程序,定量计算了互调失真与工作频率、发射极条宽、基区宽度、发射极线电流密度,基区掺杂浓度等重要参数的关系。计算结果与实验结果基本吻合。     

Analysis of envelope signal injection for improvement of RF amplifier intermodulation distortion

Adaptive bias techniques based on envelope signal power detection have been proposed for linearity enhancement and dc current reduction in RF amplifiers. Experimental results show an improvement in amplifier linearity, although asymmetric intermodulation distortion (IMD) was observed. This work rigorously studies the effects of the envelope signal injection on amplifier distortion using the Volterra series formulations. The results intuitively explain the spectral regrowth asymmetry, and point to a design technique in which third-order IMD can be optimally cancelled. The theory was verified through comparison to measurement and simulation results.     

Improvement of intermodulation distortion in microwave m.e.s.f.e.t. amplifiers using gate-bias compensation

A simple technique is described for improving the intermodulation distortion performance of microwave m.e.s.f.e.t. amplifiers. The technique utilises transistor gate-bias compensation controlled by the input signal level of the amplifier. For a constant output power of 0 dBm, an improvement in third-order intermodulation distortion product of up to 10 dB has been observed. The advantages and limitations of the technique are discussed.