Feedback Linearization of RF Power Amplifier for TETRA Standard

In wireless transmission systems, non-ideal response of different functional components along with power amplifier\u27s nonlinearity plays a major role in degrading the transmitter performance. Several parameters defines the performance of a wireless transmitter, such as adjacent channel power ratio (ACPR), error vector magnitude (EVM), spectral mask, etc., and the effect of non-ideal behaviour of the transmitter affects these parameters. For many standards these parameter specifications are defined such that the concern for transmitter linearization is very much relaxed. Standards like Terrestrial Trunked Radio (TETRA) specify strict regulation on these parameters. Therefore, the requirement of linearity is a great challenge for the design of the transmitter. Many linearization schemes is available for linearizing the nonlinear effect of a transmitter, and among those the Cartesian feedback technique is a well known concept for linearization of transmitter operating according to TETRA standard, as well as employing a narrowband operation. In our research, distortion effect of the transmitter has been analysed, and a practical demonstration of the linearization effect over distortion has been implemented using the Cartesian feedback concept

Feedback Linearization of RF Power Amplifier for TETRA Standard

In wireless transmission systems, non-ideal response of different functional components along with power amplifier’s nonlinearity plays a major role in degrading the transmitter performance.  Several parameters defines the performance of a wireless transmitter, such as adjacent channel power ratio (ACPR), error vector magnitude (EVM), spectral mask, etc., and the effect of non-ideal behaviour of the transmitter affects these parameters. For many standards these parameter specifications are defined such that the concern for transmitter linearization is very much relaxed. Standards like Terrestrial Trunked Radio (TETRA) specify strict regulation on these parameters. Therefore, the requirement of linearity is a great challenge for the design of the transmitter. Many linearization schemes is available for linearizing the nonlinear effect of a transmitter, and among those the Cartesian feedback technique is a well known concept for linearization of transmitter operating according to TETRA standard, as well as employing a narrowband operation. In our research, distortion effect of the transmitter has been analysed, and a practical demonstration of the linearization effect over distortion has been implemented using the Cartesian feedback concept

RF Power Amplifier Linearization in Professional Mobile Radio Communications Using Artificial Neural Networks

This paper is focused on the linearization of the radio frequency power amplifier of a professional digital handheld by means of an artificial neural network. The simplicity of the neural network that is used, together with the fact that a feedback path is unnecessary, makes this solution ideal to reduce both the cost of a handheld and its hardware complexity, while fully maintaining its performance. A compensation system is also needed to keep the linearization characteristics of the neural network stable against frequency, temperature, and voltage variations. The whole solution that comprises both the neural network and the compensation system has been implemented in the digital signal processor of a real handheld and afterward fully tested. It has proved to be satisfactory to meet the telecommunication standard requirements in all frequency, temperature, and voltage ranges under consideration while efficient to lower the computational cost of the handheld and to make its internal hardware simpler in comparison with other traditional linearization techniques. The results obtained demonstrate that a neural network can be used to linearize the power amplifiers that are used in transmitters of telecommunication equipment, leading to a significant reduction of both their hardware cost and complexity

Design of linear transmitters for wireless applications

Wireless standards for high data-rate communications typically employ complex modulation schemes that have large peak-to-average power ratios (PAPR), along with a significant bandwidth requirement. Transmitters for such applications often employ off-chip power amplifiers (PAs), that are typically operated in back-off, such that the peak output power is less than the output 1-dB compression point (P1dB), in order to minimize distortion. In mobile systems, architectures that can enhance the linearity of the transmit chain are highly attractive since these can reduce the PA's back-off requirement, which helps to enhance efficiency. In this dissertation, linearization techniques for mobile transmitters are explored. A Cartesian feedback-feedforward transmitter is proposed for linearity enhancement. The transmit path in the architecture is placed in a Cartesian feedback loop. The feedback error signal is applied to a Cartesian feedforward path for further linearity improvement. Linearity of the feedback-feedforward system is analyzed by using a Volterra series representation. System simulations using two-tone signals and modulated signals are also presented and are used to verify the linearity enhancement provided by the proposed architecture. A prototype transmitter IC that employs the Cartesian feedback-feedforward approach is implemented in a 0.13 μm CMOS process. Design considerations for critical transmitter circuits are discussed. A proof-of-concept Cartesian feedback-feedforward architecture that includes the prototype IC and external components is demonstrated. The implementation allows for a 8.7 dB improvement in the adjacent channel leakage ratio (ACLR), compared to an open-loop transmitter, for an output power of 16.6 dBm at 2.4 GHz while employing a 16-QAM LTE signal with 1.4 MHz bandwidth. The linearity of the Cartesian feedback-feedforward system is found to depend primarily on the loop gain of the Cartesian feedback and the linearity of the Cartesian feedforward path, which introduces a trade-off with power consumption. To enhance the linearity of the Cartesian feedback-feedforward transmitter even further within the Cartesian feedback loop, two modified Cartesian feedback-feedforward architectures are explored. System simulations show that both modified configurations can help to enhance linearity compared to the above Cartesian feedback-feedforward transmitter.Electrical and Computer Engineerin

RF Power Amplifier for TETRA Base Station

Lineaarisia tehovahvistimia tarvitaan järjestelmissä, joissa käytetään suureen spektritehokkuuteen pyrkiviä modulointimenetelmiä. Yksi tällaisista järjestelmistä on TETRA-järjestelmä (TErrestrial Trunked RAdio). Lineaariset tehovahvistimet ovat usein huonoja hyötysuhteeltaan. Siksi erilaisia linearisointimenetelmiä käytetään tehovahvistimien linearisointiin, jotta niiden hyötysuhdetta saadaan parannettua. Erilaisia linearisointimenetelmiä on esitelty tämän työn alkupuolella. Tämän työn tarkoituksena on tutkia LDMOS ja GaN tyyppisiä transistoreja ja niiden sopivuutta TETRA tukiaseman tehovahvistimiksi. Piirisimulaattoria apuna käyttäen LDMOS- ja GaN-transistorien tyypilliset ominaisuudet selvitetään ja annettujen vaatimusten mukaiset tehovahvistinkytkennät muodostetaan. Simulaatioista saatua tietoa hyödyntäen TETRA vahvistimen prototyyppi valmistetaan. Prototyyppivahvistin mitataan ja saatuja mittatuloksia verrataan simultaatiotuloksiin sekä TETRA-standardin asettamiin vaatimuksiin. Mittaustulosten perusteella LDMOS tyyppinen transistori on tutkituista transistoreista paras vaihtoehto TETRA-tehovahvistimeksi. Selvitys kuitenkin osoittaa, että jos GaN-transistorien hinta laskee, voivat ne tarjota varteen otettavan vaihtoehdon LDMOS-transistoreille TETRA-tukiasemakäyttöön.Linear power amplifiers are needed in systems, where spectrum efficient modulation methods are used. One of these systems is TETRA (TErrestrial Trunked RAdio). High linearity of power amplifier usually affects negatively its power efficiency. Therefore, different linearization methods are used to keep the power amplifier linear, while its efficiency is increased. Different linearization methods are presented in begining of this study. The scope of this thesis work is to study LDMOS and GaN transistor power amplifiers and select a suitable transistor to be used in the TETRA base station power amplifier. Using a circuit simulator, LDMOS and GaN transistor characteristics are analysed and power amplifier circuits are designed according the design specifications. Using the information derived from the simulations, a prototype of TETRA power amplifier is constructed. The constructed power amplifier circuit is then measured and the results are compared to simulation data and requirements of the TETRA standard. Based on the achieved measurement results, the LDMOS transistor is the most suitable choice to be used in TETRA power amplifier. However the study shows, that if the price of the GaN devices goes down, they may challenge LDMOS transistor, as they can offer wide frequency bandwidths with decent power efficiency and acceptable gain