Feedforward Amplifier Research Articles

Prediction of inter-modulation rejection values for the first and second adjacent channels in feed-forward linearised microwave amplifiers using closed-form expressions

Feed-forward is one of the main methods for linearising microwave power amplifiers. The level of inter-modulation rejection (IMR) values can be predicted by appropriate modelling of the feed-forward microwave amplifier. Here, we have presented closed form expressions, which can be used for predicting the IMR for the first and second adjacent channels. Fifth- and third-order nonlinear models have been used for the main and error amplifiers, respectively. The predicted values have been verified using ADS simulator and a MATLAB program.

Doherty Feed-Forward Amplifier Performance Using a Novel Crest Factor Reduction Technique

This letter describes a novel iterative crest factor reduction (CFR) technique applied to a Doherty feedforward linear power amplifier (DFFLPA). This novel CFR technique is based on repeated peak cancellations and uses a scaling factor to reduce complexity. According to our results, only three iterations result in over 4-dB reduction for a two carrier WCDMA signal. Experimental results demonstrate that the proposed algorithm was able to enhance the DFFLPA system efficiency from 11.5% to 18.3%

An Improved Design of Feed-forward Power Amplifier

An Improved Design of Feed-forward Power Amplifier

Useful Characteristics for Controlling the Cancellation Performance and Center Frequency of a Linearization Loop

The cancellation performance of a linearization loop is limited by the degree of an amplitude imbalance and a phase imbalance. A delay mismatch causes a phase variation as a function of frequency. Therefore, the cancellation performance and linearization bandwidth are limited by a delay mismatch. The expression for the effects of an amplitude imbalance, a phase imbalance, and a delay mismatch on the characteristics of a linearization loop is derived and analyzed. The simulation results are compared with the results obtained by means of using a commercial simulation tool and the exact agreement is reported. The derived equation could be used in designing a linearization loop and predicting the cancellation performance of the linearization loop usefully. Some useful characteristics, known from the simulation results obtained by using the derived equation, of a linearization loop for designing and implementing feedforward amplifiers are described in detail.

Experimental optimization of the 2nd loop configuration for feedforward amplifiers in terms of their efficiency and linearity

In this paper, we report the results of the experimental optimization of the 2nd-loop configuration for feedforward amplifiers in terms of their efficiency and linearity. We consider two parameters in the 2nd-loop of a feedforward amplifier: (i) the size ratio between the main and error amplifiers and (ii) the coupling factor of the error signal coupler. Experiments are performed using a multicarrier down-link WCDMA signal under various configurations. The measured data, which are normalized with respect to the overall power capacity of the main and error amplifiers, show that, among the different 2nd-loop configurations, the best compromised efficiency (13.4%) at a given adjacent channel leakage ratio (ACLR) level (−50 dBc) is observed for a size ratio of around 3.0 and a coupling factor of around 7.2 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 617–621, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21425

An adaptive feedforward amplifier under "Maximum Output" control method for UMTS downlink transmitters

An adaptive feedforward amplifier is implemented for a Universal Mobile Telecommunication System (UMTS) downlink channel (2110-2170 MHz). An exhaustive characterization of the space of solution has corroborated the feedforward theoretical behavior. As a result, an alternative adjustment method is proposed, called output, which entails maximizing a specific designed objective function. Besides this, an adaptive control system, based on distortion signal minimization architecture, has been fabricated in order to apply the designed method. The overall system performance achieves significant improvements such as 16.7 dB on the third-order intermodulation product, measured with a 5-MHz separated two-tone signal, 15 dB on the adjacent channel leakage ratio level and 2.7 dB on the output power level, both of them obtained with UMTS test model 1 (64 channels). The maximum output control method allows fulfilling any standard linearity specification while power efficiency is maximized so the desired tradeoff between linearity and efficiency is achieved.

Optimal Adaptation Methods and Class of Operation: Keys to Improving Feedforward Amplifier Power Efficiency

This paper studies the influences of two new adaptation methods and the class of main amplifier operation on the achievable power efficiency of the feedforward amplifier under typical design constraints. These two influences are weak for a two-tone driving signal, but they interact powerfully for a real-life high-stress signal, leading to optimal designs involving Class AB or even Class B main amplifiers, depending on the required output linearity. Assuming a code-division multiple-access signal, typical MESFETs, and an output linearity commonly used in mobile systems design, the new adaptation methods allowed relative efficiency improvements of 21% and 36% using main amplifiers biased near Class B and at Class B, respectively.

A highly efficient Doherty feedforward linear power amplifier for W-CDMA base-station applications

This paper presents a RF high-power Doherty amplifier for improving the efficiency of a 30-W feedforward linear amplifier used in wide-band code-division multiple-access (W-CDMA) base-station applications. A high-power Doherty amplifier using a single push-pull LDMOS field-effect transistor is proposed as the main amplifier of a feedforward linear amplifier. The peaking amplifier's compensation line and gate bias effects are analyzed at the 6-dB backoff point. From the experimental results of a forward-link one-carrier W-CDMA, a 2.2% power-added efficiency improvement at an adjacent channel leakage power ratio linearity of -60 dBc is achieved in comparison to a conventional feedforward class-AB amplifier.

A Study on Linearization of Intermodulation Distortion for WCDMA

A linear power amplifier is particularly emphasized on the system using a linear modulations, such as 16QAM and QPSK with pulse shaping, because intermodulation distortion which causes adjacent channel interference and co-channel interference is mostly generated in a nonlinear power amplifier. In this paper, parameters of a linearization loop, such as an amplitude imbalance, a phase imbalance and a delay mismatch, are briefly analyzed to get a specific cancellation performance and linearization bandwidth Experimental results are presented for IMT-2000 frequency band The center frequency of the feedforward amplifier is 2140MHz with 60MHz bandwidth When the average output power of feedforward amplifier is 20 Watt, the intermodulation cancellation performance is more than 28dB. In this case, the output power of feedforward amplifier reduced 3.5dB because of extra delay line loss and coupling loss. The feedforward amplifier efficiency is more than 7% for multicarrier signals.

Feedforward 선형 전력증폭기를 위한 에러증폭기의 구현 및 성능평가에 관한 연구

In this paper. We tested and fabricated the error amplifier for the 15 Watt linear power amplifier for the IMT-2000 baseband station. The error amplifier was comprised of subtractor for detecting intermodulation distortion, variable attenuator for control amplitude, variable phase shifter for control phase, low power amplifier and high power amplifier. This component was designed on the RO4350 substrate and integrated the aluminum case with active biasing circuit. For suppression of spurious, the through capacitance was used. The characteristics of error amplifier measured up to 45 dB gain, 0.66 dB gain flatness and -15 dB input return loss. Results of application to the 15 Watt feedforward Linear Power Amplifier, the error amplifier improved with 27 dB cancellation from 34 dBc to 61 dBc IM.

A robust feedforward compensation scheme for multistage operational transconductance amplifiers with no Miller capacitors

A multistage operational transconductance amplifier with a feedforward compensation scheme which does not use Miller capacitors is introduced. The compensation scheme uses the positive phase shift of left-half-plane (LHP) zeroes caused by the feedforward path to cancel the negative phase shift of poles to achieve a good phase margin. A two-stage path increases further the low frequency gain while a feedforward single-stage amplifier makes the circuit faster. The amplifier bandwidth is not compromised by the absence of the traditional pole-splitting effect of Miller compensation, resulting in a high-gain wideband amplifier. The capacitors of a capacitive amplifier using the proposed techniques can be varied more than a decade without significant settling time degradation. Experimental results for a prototype fabricated in an AMI 0.5-μm CMOS process show DC gain of around 90 dB and a 1% settling time of 15 ns for a load capacitor of 12 pF. The power supply used is ±1.25 V.

Optimization for error-canceling loop of the feedforward amplifier using a new system-level mathematical model

We present a system-level mathematical model to simulate the linearity of the feedforward amplifier. The model has fundamental and distortion signal sub-paths constructed from the data extracted by baseband system simulation. The calculated linearization performances using the model have been validated by comparison with the baseband system simulation results. From the calculated results, the optimum design of the error amplifier size and coupling factor of the output coupler for a down-link WCDMA signal with 16 data channels are provided to maximally achieve output linearity with a fixed power capacity of the amplifiers. Our data shows that the optimum size of the error amplifier is 0.45 times that of the main amplifier with the coupling factor of 5.5 dB.

Optimization of feedforward amplifier power efficiency on the basis of drive statistics

Among power amplifier linearization techniques, feedforward delivers the best performance, but at the cost of significant degradation in the amplifier's power efficiency. This paper details a procedure to design feedforward amplifiers for optimal DC-RF conversion efficiency. The procedure has the convenience of requiring only the power statistics of the driving signal, of being computationally efficient, and of lending itself to a highly intuitive graphical representation. The gains and normalized saturated output powers of the main and error amplifiers, as well as the various couplings, are optimized for a specified linearity and gain at the output of the system. The amplifier types and adaptation methods employed must be specified at the outset, but results are presented that begin to reveal the impact of these factors on efficiency and, thus, to demonstrate the investigative potential of the procedure.

Comments on "Improvement of broadband feedforward amplifier using photonic bandgap"

A number of technical facts were either claimed or implied in the letter by J. Yoon and C. Seo (see ibid., vol.11, no.11, p.450-2, Nov. 2001). Without clarification or supporting data, the claims presented could mislead the reader into drawing inaccurate conclusions regarding the performance increase of feed forward amplifiers due to the so-called photonic bandgap structure.

Carrier reuse with gain compression and feed-forward semiconductor optical amplifiers

The results of two techniques for optical carrier regeneration and wavelength reuse using semiconductor optical amplifiers (SOAs) are presented in this paper. The main objective is to recover an optical carrier by erasing its amplitude modulation. The first technique employs gain compression of deeply saturated SOAs. The second technique uses a feed-forward approach, where a delayed current signal is injected into the SOA with the same shape of the incoming optical pulse. The second technique could be capable to recover the optical carrier with less than 3-dB noise. However, it was observed that the SOA gain recovery time limits the maximum usable bit rate. Theoretical simulation showed good agreement with experimental results.

Broadband DSP based feedforward amplifier lineariser

The performance of the feedforward linearisation technique begins to degrade for signals with very wide bandwidths due to the non-ideal amplitude and phase frequency response of the components. By implementing part of the lineariser in a digital signal processor (DSP), a digital equaliser can be used to compensate for the nonideal behaviour and improve the cancellation in the first loop.

Improvement of broadband feedforward amplifier using photonic bandgap

In this paper, the photonic bandgap, the predistortion, and the secondary harmonic tuning are simultaneously employed in a feedforward amplifier to maximize the power added efficiency (PAE) and the operating bandwidth for in IMT-2000 band. In this case, the secondary harmonic tuning and the predistortion linearizer can cancel the second and the third harmonics, respectively. The PBG prevented any more harmonics appearing over 6 GHz. The feedforward amplifier was improved by 4%, and 15 dBc in the PAE and the IMD (intermodulation distortion), respectively. The operation bandwidth achieved was twice as wide as the conventional feedforward amplifier.

Optical regeneration using a feedforward semiconductor optical amplifier with chirp‐controlled filtering

AbstractOptical pulse regeneration and reshaping using nonlinear optical pulse amplification followed by a chirp‐controlled filtering is simulated. The nonlinear amplification and chirp control are obtained by feedforward current injection in a semiconductor optical amplifier. The nonlinear amplification provides pulse regeneration, and the controlled chirp, in association with an optical frequency discriminator, can be used to optimize the shape of several Gbit/s pulse streams. The simulator model has been confirmed experimentally using eye diagram techniques. In addition, the switching action of an optical semiconductor amplifier with a dynamically arbitrarily injected current can be simulated. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 438–442, 2001.

Microwave feed-forward low noise amplifier designforcellular base station

A novel, cellular base station, microwave amplifier network, utilising a feed-forward design is described. A low noise figure and high small signal linearity are simultaneously achieved. Encouraging results from both a theoretical analysis and a practical implementation are presented.

Design and characterization of a microwave feed-forward amplifier with improved wide-band distortion cancellation

A new approach to the design of a wide-band feed-forward amplifier (FFAMP) is presented in this paper. Phase equalizers are employed in an FFAMP to match the nonlinear delay/phase characteristics of the main and error amplifiers, improving phase balances within the cancellation loops and providing improvement in signal cancellations over a wide bandwidth. The proposed 1.7-1.9-GHz FFAMP was fabricated and characterized. The conventional FFAMP obtains an average of 15-dB third-order intermodulation (IM3) distortion cancellation over the whole bandwidth. With the phase equalizers, the proposed FFAMP achieves a further 6-dB reduction on IM3 level.