A Nevv Method of Third-Order Intermodulation Reduction in Nonlinear Microwave Systems

Third-order intermodulation distortion (IMD (3)) of some microwave systems has been analyzed using Vollterra series. In this paper, theoretical results which have been calculated with a nonlinear FET model show that third-order intermodulation prodgcts of two input signals at f/sub 1/ and f/sub 2/ can be reduced by several orders of magnitude (in fact, theoretically, IMD (3) should be reduced to zero), with a low-frequency feedback at f/sub 1/- f/sub 2/, when the amplitude and the phase of this feedback are correctly chosen. To verify this prediction, a circuit has been realized and measurements have been made on a one-stage FET amplifier. First results confirm our analysis. Experimental measurements show a 12-dB decrease of intermodulation products with our method.     

An MMAC C-band FET feedback power amplifier

A feedback power amplifier using miniaturized microwave active circuit (MMAC) technology was developed for satellite C-band applications. This design demonstrates that a strong negative feedback can be implemented in the microwave frequencies to improve amplifier linearity and output power over a 750 MHz bandwidth. The amplifier provides a third-order intermodulation distortion improvement of 7 to 9 dB across the band at backoff, compared to results obtained using the conventional approach without feedback. The theory, proof-of-concept experiment, design, and MMAC implementation of the feedback amplifier are presented     

A highly linear 125-MHz CMOS switched-resistor programmable-gain amplifier

A highly linear programmable-gain amplifier (PGA) is fabricated using a 0.35-/spl mu/m CMOS technology. High linearity and constant wide bandwidth are achieved by using a high-gain amplifier with low input impedance and resistor-network feedback. The voltage gain is varied by digitally controlling the input switched resistors. The distortion of a switched resistor has been analyzed using the Volterra series. The PGA has a voltage gain varying from 0 to 19 dB, while maintaining a constant bandwidth of 125 MHz. The third-order intermodulation distortion is -86dB at 10 MHz. The circuit dissipates 21 mW from a 3.3-V supply.     

Third-order intermodulation distortion in microwave amplifier

Third-order intermodulation distortions of a microwave GaAs f.e.t. amplifier are analysed using a simple nonlinear model for the device. If the amplifier has strong feedback at low frequencies, the second-order interactions may dominate and degrade the third-order distortions. Solutions are presented to eliminate this distortion degradation. The analysis is very well substantiated by measurements.     

Theoretical Analysis of Intermodulation Distortion of Reflection-Type IMPATT Amplifiers

The basic equations for a reflection-type IMPATT amplifier are used to derive expressions for the output when the amplifier is driven by a multifrequency input signal. The third-order intermodulation distortion is expressed and graphically presented for various diode, circuit, and signal parameters. The results provide a guideline for designing amplifiers with minimum intermodulation distortion or prescribed distortion level.     

Dynamic Theory of Intermodulation Distortion

This paper studies the third-order intermodulation distortion of signals in a reflection amplifier that are separated by an appreciable fraction of the bandwidth. This large separation of input signals requires taking account of the energy interchange between diode and circuit. A theory of intermodulation distortion accounting for this interaction is developed for large-order nonlinearities. Previous analyses of this problem have been limited to small nonlinearities and small separation of the input signals. Experimental verification of the theory developed here is demonstrated for an IMPATT diode reflection amplifier as a function of power level and tone separation.     

A 100-MHz CMOS wide-band IF amplifier

When the data rates of communication systems increase, wideband IF amplifiers are needed. It is also possible to use a single wideband intermediate frequency (IF) amplifier for a radio band with several narrow-band channels of varying strengths. The linearity is then critical, if intermodulation products are not to disturb weak channels. We try to find a topology for this new amplifier application, suitable for integration in a standard CMOS process. To get low distortion, we use an output stage with high linearity, which is further linearized by feedback in a double-nested Miller configuration. A 0.8-μm standard CMOS IF amplifier design with low distortion up to 20 MHz is presented     

一种改进型免滤波D类音频放大器的设计

本文描述了一种基于华虹NEC0.35μmBCD工艺的改进型免滤波D类音频放大器。这种创新的结构基于归一化脉冲宽度调制技术,通过对回路滤波的输出信号进行合理的采样与保持,同时采用迟滞比较和反馈回路控制技术,很好地解决了传统脉宽调制方法中对于互调失真抑制能力较差的问题。     

Measurement technique for characterizing memory effects in RF poweramplifiers

Memory effects are defined as changes in the amplitude and phase of distortion components caused by changes in modulation frequency. These are particularly important in cancelling linearizer systems, e.g., when distortion is reduced by similar distortion in the opposite phase. This paper begins by describing electrical and electrothermal causes for memory effects. A three-tone test setup is then constructed to measure the phase of third-order intermodulation distortion products. This paper also presents the measured results for a bipolar junction transistor and a MESFET amplifier     

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.     

A 0.02% THD and 80 dB PSRR filterless class D amplifier with direct lithium battery hookup in mobile application

This paper presents a fully integrated CMOS filterless class D amplifier that can directly hook up lithium battery in mobile application The proposed amplifier embodies a 2-order feedback path architecture instead of direct feedback of output to input of the integrator to decrease the high frequency intermodulation distortion associated with direct feedback and eliminate the integrator input common mode disturbance from the output in ternary modulation. The prototype class D amplifier realized in 0.35μm digital technology achieves a THD+N of 0.02% when delivering 400 mW to an 8Ω load from V_DD=3.6 V. The PSRR of the prototype class D amplifier is 80 dB at 217 Hz. Furthermore a filterless method that can eliminate the external LC filter is employed which offers great advantages of saving PCB space and lowering system cost. In addition the prototype class D amplifier can operate in large voltage range with V_DD range from 2.5 to 4.2 V in mobile application. The total area of the amplifier is 1.7 mm².     

前馈系统中辅助放大器非线性分析

前馈系统中由于信号对消环路失配,导致在辅助功放输入端载波信号无法完全对消,辅助放大器的再次非线性失真会影响整个系统的失真。本文研究了残余载波信号再次产生的互调失真对整个系统线性化指标的影响,并给出了系统性能与电路参数和幅度、相位失配的关系式,通过这个关系式可以计算出要达到特定载波互调比时所需器件的最低指标要求。     

基于ADS平台不对称Doherty功率放大器的仿真设计

为在高线性的前提下提高WCDMA基站系统中功率放大器的效率,仿真设计了一款工作于2.14 GHz频段不对称功率驱动的Doherty功率放大器。基于ADS平台,采用MRF6S21140H LDMOS晶体管,通过优化载波放大器和峰值放大器的栅极偏置电压改善三阶互调失真(IMD3),同时通过调节输入功率分配比例改善由于峰值放大器对载波放大器牵引不足导致的失配问题,从而改善不对称Doherty功率放大器的输出性能。仿真结果表明,当载波放大器的栅极偏置电压为2.84 V,峰值放大器的栅极偏置电压为0.85 V并且输入功率比例为1:2.3,输出功率为44 dBm时其功率附加效率(PAE)为24.21%,IMD3为-44.46 dBc,和传统AB类平衡功率放大器相比PAE提高了8.58%,IMD3改善了6.98 dBc。     

A wide-band ultralinear amplifier from 3 to 300 MHz

The design of a low-distortion, wide-band amplifier with 75-/spl Omega/ input and output impedances is described. Simultaneous shunt and series feedback is used and design equations are derived for terminal impedances, forward gain, loop gain, and noise figure. The advantages of a Darlington connection for low distortion are described. For 0-dBm signal levels, the amplifier achieves third-order intermodulation products of -88 dB relative to the carrier at 300 MHz and 12 channel cross-modulation (CM) of -77 dB at channel 13.     

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.     

Highly linear RF amplifier design: theoretical analysis and experimental study

In this article, a high frequency amplifier design method based on the negative impedance compensation has been demonstrated analytically and experimentally. An effective nonlinear model has been used to simulate the harmonic distortion and intermodulation distortion factors in amplifier design. The simulation and measurement results show that, with this proposed technique, high linearity and high gain accuracy can be achieved. The proposed method is particularly suitable for linearisation of RF/microwave amplifiers with low open–loop gain.     

Experimental performance of an adaptive digital linearized poweramplifier [for cellular telephony]

Amplification of linear modulation schemes, (which exhibit fluctuating envelopes), by high power amplifiers invariably leads to the generation of distortion and intermodulation products. Recent theoretical work has suggested that a complex gain predistorter may be employed to linearize a nonlinear power amplifier. The authors present experimental results demonstrating that a reduction in out-of-band spectra in excess of 20 dB may be achieved by employing digital feedback and a complex gain predistorter     

Linearisation of microwave power amplifiers using active feedback networks

A new technique for linearising microwave power amplifiers is presented. Analytical and experimental results show that the intermodulation distortion in power amplifiers can be seriously reduced when active feedback networks are employed.     

Intermodulation nulling in HEMT common source amplifiers

A new model of the second- and third-order intermodulation products from HEMT and MESFET small-signal amplifiers, resulting from nonlinear drain-source current has been proposed in our previous publications. Based on this model, intermodulation nulling conditions in terms of the Taylor series coefficients, hence in terms of bias, have been investigated. This paper now examines the load dependence of the second- and third-order intermodulation products in HEMT small-signal common source amplifiers. Intermodulation nulling conditions are proposed and validated. This is useful in designing a high performance amplifier by calculation of optimum load for minimum distortion and studying distortion generation as a function of circuit topology     

Calculating the CSO/CTB spectrum of CATV amplifiers and opticalreceivers

The discrete CSO/CTB intermodulation distortion has a big influence on the CATV net quality. This article describes a new method to calculate the composite second order (CSO) and composite triple beat (CTB) intermodulation distortion spectrum for the full frequency range of a coaxial cable CATV amplifier for any input frequency plan. The calculation takes into account the output level ripple and preemphasis, using frequency dependent intermodulation coefficients. These coefficients have been established through CSO/CTB measurements on multichannel test systems for standard frequency plans at 5-8 intermodulation frequencies or on distortion arrays for the two (three) oscillator measuring test system. The defined intermodulation coefficients are unrelated to the frequency plan and the input/output level ripple. It is also possible to calculate the CSO/CTB spectrum caused by analogue channels within digital QAM channels. The results equally apply to optical CATV receivers. Simulation results have been verified using extensive data from multichannel measurement systems