High efficiency power amplifier for high frequency radio transmitters

Abstract

Abstract-Modern transmitters usually have to amplify and transmit complex communication signals with simultaneous envelope and phase modulation. Due to this property of the transmitted signal, linear power amplifiers (class A, B or AB) are usually employed as a solution for the power amplifier stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has high peak-to-average power ratio. The Kahn envelope elimination and restoration (EER) technique is used to enhance efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents solutions for the power supply that acts as the envelope amplifier and class E amplifier that is used as a nonlinear amplifier. The envelope amplifier is implemented as a multilevel converter in series with a linear regulator and can provide up to 100 W of peak power and reproduce sine wave of 2 MHz, while the implemented class E amplifier operates at 120 MHz with an efficiency near to 90%. The envelope amplifier and class E amplifier have been integrated in order to implement the Kahn's technique transmitter and series of experiments have been conducted in order to characterize the implemented transmitter.

Serial or parallel linear-assisted switching converter as envelope amplifier: Optimization and comparison

“…Another possibility for the envelope amplifier is to use a multilevel converter in series with a linear regulator [3,7] as it is shown in Figure 11. In this case, the linear regulator conducts the whole load current and the multilevel converter supplies the linear regulator with appropriate voltage levels in order to decrease the power losses in the linear regulator.…”

“…Techniques based on envelope tracking (ET) and envelope elimination and restoration (EER) have demonstrated their potential for next generation communication systems [1][2][3]. Both techniques have in common that it is necessary to modulate the supply voltage of the amplifier and it is done using an envelope amplifier (modulator) like in Figure 1.…”

“…In the state of the art there is a wide variety of solutions for the envelope amplifier depending on the power it has to process and the required bandwidt. In [4][5] solutions based on simple buck converter are proposed, while in [1][2][3][6][7][8] solution based on switching converter in parallel and series with a linear regulator are presented.…”

Cascode class-E power amplifier in 180/350 nm CMOS for EER system

“…Envelope elimination and restoration (EER) is a widespread technique [1,2,3] for amplification of nonconstant envelope modulated signals. Functional scheme of this system is shown on Fig.…”

High efficiency power amplifier based on envelope elimination and restoration technique

“…Figure 9 shows the implemented EER transmitter. In [16] the results of the efficiency measurements in the case of a simple AM modulation have been presented. It has been demonstrated that the efficiency of the implemented EER PA is significantly higher than the theoretical efficiency of the class B amplifier when the signals with high PAPR (Peak to Average Power Ratio) are transmitted.…”