Two-Tone and Nine-Tone Excitations in Future Adaptive Predistorted Linearised Basestation Amplifiers of Cellular Radio

Linearisation of a radio basestation amplifier using a third order, a fifth order and a seventh order predistortion scheme is studied. Adaptive predistortion using a third order predistorter improved the amplifier intermodulation distortion (IMD) by between 6.4 dB and 33 dB from the third IMD power level (i.e., maximum power amplitude variation of the IMD), provided by the raw amplifier, as measured by a two tone test. The variation in improvement is due to changes in the input power level. Improvement increases as the input power is backed off from the 1 dB compression point. A fifth order predistorter will give an IMD improvement of 8.7 dB and 48.4 dB if properly adjusted. A seventh order predistorter (with the fifth complex coefficient fixed to zero) will show the best performance, particularly throughout a window (approximately from 1.5 dB to 3 dB away from the 1 dB compression point). The IMD improvement throughout this window within the high input range measures between 9.1 dB to 21.7 dB over that achieved with a fifth order predistorter. For a nine-tone test (with uniformly distributed random phase), a third order predistorter will hardly improve the worst IMD power level, provided by the raw amplifier. A fifth order predistorter, if properly adapted will give an IMD improvement of between 8.8 dB and 41.5 dB from the worst IMD level while a seventh order predistorter will give a close performance to that of a fifth order one. Fixing the predistorter coefficients enables a comparative study of the IMD power level improvement between 5th order fixed and adaptive predistorters, for a nine-tone excitation. A 5th order predistorter with its coefficients fixed to those values obtained for optimum IMD level at a backed-off power input value of 8.5 dB from the 1 dB compression point is found to maintain an IMD power variation better than 55 dB from fundamental power level, throughout the input range, up to the backed-off value.     

A 60-W Multicarrier WCDMA Power Amplifier Using an RF Predistorter

In this brief, we present a 60-W power amplifier that is linearized using an RF predistorter for multicarrier wideband code-division multiple-access (WCDMA) applications. The proposed RF predistorter is fully composed of RF or analog circuits, and it has a moderate memory effect compensation capability using a delayed third-order intermodulation (IM3) component path. It also includes the IM5 generation circuits and a compact IM3 generator that is capable of autocanceling for the fundamental component. The proposed RF predistorter was implemented and applied to a 60-W high-power WCDMA amplifier. For a four-carrier downlink WCDMA signal, the RF predistorter improved the adjacent channel leakage power ratio at a 5-MHz offset by 6.19 dB at an average output power of 48 dBm. The total efficiency of the system is as high as 13.6% at the same output power level. At an output power level of 60 W, the linearized power amplifier complies with the linearity specification of the WCDMA system.     

一种基于双查找表自适应预失真结构的射频功率放大器线性化方法

同其它使用简单函数实现数据查找表索引的自适应预失真结构不同，本文采用专门的地址查找表来实现数据查找表索引，组成了双查找表结构的自适应预失真器。仿真结果表明，采用本文方法可以使得射频功率放大器对相邻信道的干扰得到25dB以上的性能改善。     

Performance optimization of radio-on-fiber systems employing erbium doped fiber amplifier for optical single sideband signals considering intermodulation distortion

The performances of radio on fiber (RoF) systems with a dual-electrode Mach-Zehnder modulator and an erbium-doped fiber amplifier (EDFA) are optimized by numerical equations including the third order intermodulation (IM3) as well as amplified spontaneous emission (ASE) noise. We investigate a signal-to-noise-and-distortion ratio (SNDR) considering fiber dispersion with respect to an input signal power and an EDFA gain in both noise-dominant and third order intermodulation (IM3)-dominant cases. We also verify that the numerical analysis results are well matched with those of a commercial simulator, VPItransmissionMaker. In the analysis results, the optimum input signal power for the maximum SNDR of a RoF system with EDFA was reduced over 8 dB compared with that without EDFA. The dramatic reduction of IM3 power at a receiver was resulted from this decrement of input signal power. Thus, the maximum SNDR of the system with EDFA was obtained over 17 dB at 40 km fiber compared with that of the system without EDFA. In addition, the results showed that the SNDR was efficiently improved by EDFA in the noise-dominant case, while the SNDR improvement was negligible by EDFA in the IM3 dominant case.     

Amplifier linearization using a digital predistorter with fastadaptation and low memory requirements

A method is described for linearizing a power amplifier by predistorting its input. It is particularly well suited to baseband implementation with digital signal processor hardware. In comparison with the most powerful previously published predistorter, it requires four orders of magnitude less memory, reduces convergence time by over three orders of magnitude, eliminates reconvergence time following a channel switch, and eliminates the need for a phase shifter in the feedback path. The predistorter structure is described. Its ability to suppress intermodulation products using only a small table is demonstrated. The effect of predistorter nonidealities (especially limited table size) on the power amplifier's output are analyzed. A fast adaptation algorithm is introduced     

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     

Linearization of receivers using envelope signal injection

This paper presents a new linearization method for receivers employing envelope signal injection. In this technique, the third-order intermodulation distortion (IM3), at the output of a mixer in IF band, is cancelled by injecting the envelope of the RF input signal to both the low noise amplifier (LNA) and the mixer. By properly adjusting the amplitude and polarity of the injected envelope signal, up to 40-dB improvement of the IM3 and 11-dB improvement of the IM5 is obtained in a two tone test with 100-kHz separation at 1.9GHz. This method operates very well over a wide range of power up to the 1-dB compression point of the receiver. The noise performance of the receiver under this linearization technique is also investigated. The noise floor at the output of the receiver is increased by 0.8 dB only when the system is optimized for linearity.     

New predistortion linearizer using low-frequency even-orderintermodulation components

We present two types of new predistortion linearizers using low-frequency even-order components. One adopts an in-phase and quadrature balanced modulator as a generator of the third-order intermodulation (IM3) and fifth-order intermodulation (IM5) components and the other adopts a double-balanced diode mixer. Both types are very compact and could independently control the amplitudes and phases of the intermodulation (IM) components. We have analyzed the delay mismatch effect of these predistortion circuits. The result shows that the IM5 components are twice as sensitive than the third ones. Two types of predistorters are implemented and tested at the International Mobile Telecommunications-2000 band. Two tone test results show that the IM3 cancellation is about 23-25 dB and the IM5 is cancelled by about 12-20 dB for both cases. The adjacent channel power ratio is improved by over 11 dB at the broad-band CDMA signal with a chip rate of 4.096 Mc/s, and this improvement is maintained through a broad range of output power level     

A distortion control technique for achieving high power efficiency in an HPA array

This paper proposes a new technique for reducing the intermodulation (IM) distortion products in a high-power amplifier (HPA) array. The proposed technique dissolves the relations between carriers and IMs by applying IM phase control. As a result, IMs are distributed to all the output ports in the array, and the carrier power to intermodulation power ratio (C/IM) of the HPA array can be increased. The improvement in CI/M is as high as 10log N dB, where N is the number of HPAs. Newly developed even-order distortion implemented intermodulation distortion controllers (EODICs) are used to achieve the IM phase control. A test carried out using a four-parallel HPA array with EODICs confirms that the technique noticeably improves C/IM and demonstrates its validity.     

Linearization of mixers using predistortion and envelope signal injection

This letter presents a new linearization method for mixers employing predistortion and envelope signal injection. In this technique the third order intermodulation distortion (IM3), at the output of a mixer in IF band, was cancelled by using a diode predistortor and injecting the envelope of the RF input signal to both the predistortor and the mixer. By properly adjusting the amplitude and polarity of the injected envelope signal, up to 26 dB improvement of the IM3 is obtained in a two tone test with 100 kHz separation at 1.9 GHz. This method operates very well over a wide range of output power up to the 1 dB compression point of the mixer.     

Highly Linear Predistortion Power Amplifiers With Phase-Controlled Error Generator

A simple predistortion technique to cancel the fifth-order intermodulation (IM5) as well as third-order intermodulation (IM3) components using a third-order predistorter (PD) is represented. The IM3 and IM5 components are cancelled out simultaneously by their same magnitude and phase difference in the PD and power amplifier (PA). Moreover, this phase difference is controlled by using the phase-controlled error generator in the PD. For experimental verification, a third-order PD has been implemented and tested in a 30-W class-AB PA at the wide-band code division multiple access (WCDMA) band of 2.11-2.17GHz. Two-tone test results show that significant cancellation of the IM3 and IM5 components can be obtained. For a four-carrier WCDMA application, significant adjacent channel leakage ratio improvement is achieved over a wide range of output power levels     

Broadband analogue predistortion using a distortion generator based on two-stage RF mixer topology

An analogue predistorter using a distortion generator based on a two-stage radio frequency mixer topology is presented. The proposed distortion generator achieves fundamental signal cancellation without using a signal cancellation loop or a resonant circuit, thus it generates an error signal that predominantly consists of unwanted intermodulation distortion (IMD). Measurements are performed using multi-tones, WLAN- and Terrestrial Trunked Radio (TETRA)-modulated signals. Distortion generator provides high levels of IMD and achieves more than 40 dB fundamental signal cancellation across a bandwidth of 120 MHz. A proof-of-concept predistorter was constructed to validate the usefulness of the proposed distortion generator, which achieves up to 15 dB suppression of IMD and adjacent channel power ratio at the output of a power amplifier. Distortion generator and predistorter gave similar results at multiple frequencies between 920 MHz and 2 GHz, with different test signals having bandwidths ranging from 25 kHz to 120 MHz.     

Intermodulation in multiple fixed beam distributed amplifier phased array antenna systems

In the recent development of phased array/distributed amplifier systems for application to mobile satellite or thin route communication systems, the intermodulation (IM) generated by the element amplifiers is spatially dispersed in such a way that some of the IM radiated energy falls outside the intended beam area. In addition, some of the IM falling inside the beam area has frequencies different from the carriers intended for that area. It is known that for fixed beam systems with frequency reuse, an average IM noise reduction of several dB can be realized. In the specific case under investigation, of four beams, nine frequencies and 12 carriers (1-33 frequency reuse factor), an IM improvement of about 2-0 dB is realized. The improvement in carrier-to-IM-noise ratio can be applied to increase system capacity, or for given capacity it can be used to reduce RF power amplifier back-off, which can be translated into a reduction of spacecraft prime power requirement. The considerable advantage gained from the multiple beam distributed amplifier approach makes it worthwhile to explore the workings of such a system and other benefits it may offer. One of the benefits is a common RF power pool for all carriers and beams, and the other is the spatial dispersion of intermodulation (IM). A satellite multiple beam pattern and the spatial dispersion of IM products are shown in Figure 1.     

Polynomial 2.1 GHz RF predistorter IC with envelope injection output

This paper presents the structure, test setup and measured results of a polynomial RF predistorter IC fabricated in a 0.35 μm SiGe BiCMOS process. The predistorter is designed for the base station WCDMA band at 2.1 GHz. The predistortion signal is generated by a 5th-degree complex polynomial. Also a squared envelope is generated that can be used as a baseband injection signal to cancel 2nd-order distortion that typically causes memory effects. The performance of the predistorter was measured by driving a three-stage discrete power amplifier chain by a 2-tone test and a 3.84 MHz wide 3GPP WCDMA modulated signal. The 2-tone test showed more than 20 dB IM3 cancellation and the WCDMA signal’s ACPR was improved by 8 dB.     

Intermodulation distortion in high dynamic range microwavefiber-optic links with linearized modulators

Linearization of integrated optic intensity modulators significantly reduces the two-tone intermodulation distortion. The resulting intermodulation distortion produced by these modulators then varies as the input power to the fifth-order link system, the overall intermodulation product is a combination of third-order and higher-order terms. The authors determine the dynamic range of a cascaded microwave network consisting of a preamplifier, a high-dynamic-range fiber-optic link with a highly linear modulator, and a postamplifier. An expression is found that relates the intermodulation power at the output to the relative suppression from the signal level. As an example, a hypothetical 10-GHz low-distortion fiber-optic link that has a dynamic range of 125 dB in a bandwidth of 1 Hz is cascaded with various preamplifiers, and it is shown that the dynamic range of the system is reduced by as much as 20 dB, depending on the third-order intercept of the amplifier     

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.     

宽带系统中有记忆大功率功放的数字预失真器研究

针对高峰均比的宽带输入信号,提出了一套联合峰均比抑制技术和基带自适应预失真技术的数字预失真器设计方案,并仿真了峰值抵消算法和自适应预失真算法.结果表明对于峰均比为8.4 dB的输入信号,经过1.5 dB的削峰处理后,预失真器改善带外频谱抑制27 dB,非常有效地补偿了功放的非线性失真,提高了功放效率,对发射机功放线性化技术有一定的实用价值.     

简洁构型与馈电的宽带双极化金属锥阵列天线北大核心CSCD

本文提出了一种宽带双极化金属锥阵列天线。该阵列天线以传统的旋转体天线结构为主体,通过在锥体底部开设四道正交的直通槽,以便在锥状单元内部形成可与地板间构成匹配谐振腔的开放式空腔结构。在阵列中,任意两个相邻的锥状单元之间可形成类似于Vivaldi天线的辐射缝隙结构。馈电采用同轴馈电方式,探针无弯折结构,金属锥体无弯折过孔。每个金属锥状单元独立,可极大简化加工、装配和维护过程。该天线具有两个正交极化,分别由左右和前后相邻单元构成。仿真结果表明,在频率范围为2～8GHz内,阵列大部分有源VSWR小于2,小部分端口有源VSWR小于2.5 (相对带宽为120%)。     

A highly linear CMOS Gm-C bandpass filter with on-chipfrequency tuning

A fourteenth-order CMOS transconductance-C (G_m-C) bandpass filter with on-chip automatic frequency tuning is described. By using highly linear G_m-C integrators, the filter achieves 75 dB dynamic range over 700 kHz noise bandwidth. The measured intermodulation distortion (IM3) @ 600 kHz for a 4 V_pp input signal is only -61 dB. On-chip automatic frequency tuning provides more than 300% center frequency range (i.e., 165-505 kHz) of the filter with ±1% frequency accuracy. The 0.7-μm CMOS filter measures 4.8 mm ² and consumes 70 mW from a single 5 V power supply     

Highest efficiency, linear X-band performance using InP DHBTs - 48%PAE at 30 dB C/IM3

InP single heterojunction bipolar transistors have previously demonstrated 5-10 dB lower third-order intermodulation products (IM3) compared to GaAs heterojunction bipolar transistors (HBTs) under low voltage (2 V) operation. This paper reports excellent single-tone and two-tone X-band operation, including high two-tone power-added efficiency (PAE), on linear InP double heterojunction bipolar transistors (DHBTs) operated at V_ce=4 V. The InP DHBT demonstrated a 30 dB carrier to third-order intermodulation product (C/IM3) output power ratio simultaneously with 48% two-tone PAE. This is the highest known efficiency of an X-band device under linear (30 dB C/IM3) operation. This is especially significant for microwave power amplifiers for satellite communication transmitters, where lower intermodulation distortion is normally accomplished by backing off in RF drive and output power, thus sacrificing PAE performance