Linearization of Highly-Efficient Monolithic Class E SiGe Power Amplifiers with Envelope-Tracking (ET) and Envelope-Elimination-and-Restoration (EER) at 900MHz

Abstract

The linearization of highly efficient monolithic SiGe Class E power amplifiers (PAs) using both EnvelopeTracking (ET) and Envelope-Elimination-and-Restoration (EER) techniques has been studied at 900MHz. Without applying any linearization, the fully-integrated SiGe PAs achieve power-added efficiency (PAE) of 66% with no offchip matching. The overall PAE of an ET-linearized PA system is 45% at an output power of 20dBm for an 881MHz EDGE (Enhanced Data Rate for GSM Evolution) modulated signal. The ET-linearized PAs pass the stringent EDGE transmit spectrum mask, but the EER-linearized PAs do not. The PAE of the ET system is expected to reach~50% with further efficiency improvement on the envelope amplifier.

Design of highly-efficient wideband RF polar transmitters using the Envelope-Tracking technique

“…Switch-mode PAs are highly efficient but intrinsically nonlinear so they need to be linearized for non-constant envelope applications. Classical ET techniques have been applied mainly to current-mode PAs [14][15][16], however our recent work indicates that ET can be extended to the class E PAs and provide better linearization than EER [17][18]49]. Two principal sources of nonlinear distortion were mentioned by Raab for ET/EER systems, i.e., finite envelope bandwidth and differential delay between amplitude and RF signal [52].…”

“…The average PAE for class AB PA with high PAR signals, therefore, is quite poor and this is a major barrier for battery size reduction. It is possible, however, to achieve a significant improvement in wideband PAE using monolithic switch-mode PA by using envelope tracking (ET) [17][18]. For base station applications, this ET technique has proven to offer considerable reduction in heat dissipation for 3G, WiMAX and DVB transmitters [24,[34][35] Specifically, in ET-based large-signal polar transmitter, the voltage supplied to the final stage of the RF PA is changed dynamically, synchronized with the RF signal passing through the device to ensure that the PA remains saturated and efficient.…”

“…This is because the PA is "nearly saturated" but not always fully saturated as in the case of EER; 2. Lower sensitivity to timing mismatch between the RF vs. amplitude paths than EER [14,16,18]; 3. Lower bandwidth requirement for the envelope amplifier than that in the case of EER [14,16].…”

“…We have used somewhat similar design methodology for sub-optimal but fully-monolithic SiGe PAs and achieve 66% PAE at 900MHz and 62% at 2.4GHz [18,[48][49][50][51].…”

“…In the past, polar transmitters were mostly used for high-power base station applications to effectively reduce heat dissipation; however, they have recently become very successful for wireless handset TX design in volume production due to their significant better efficiency and lower cost [5][6][7][8][9][10][11][12][13]. One latest development is to apply the Envelope-Tracking (ET) technique to implement monolithic large-signal polar transmitters for wireless applications, as excellent system efficiency and linearity has been demonstrated, which is the focus of this paper [14][15][16][17][18][19]. We will begin our discussions of ET-based polar transmitters by briefly reviewing some state-of-the-art monolithic RF polar transmitters for handset applications next.…”