Dynamic biasing in SiGe HBT for wideband step envelope tracking power amplifiers

Abstract

This article investigates the use of reconfigurable class-AB power amplifiers in wideband step envelope tracking (SET) architectures. The experimental results are related to a SiGe-HBT power-device prototype in which a dynamic switching capability has been integrated. The SET architecture is complemented by a digital predistortion algorithm and the resulting structure (circuit plus algorithm) is analyzed at system level. As a result, the SiGe prototype is capable to provide 20 dBm total output power with EVM 5 5.1%. In the case of 802.11g and WCDMA signals the proposed approach gives a relative average PAE enhancement in excess of 46% with respect to traditional class-AB RF power amplifiers.

Power amplifier architectures with discrete power control for high average efficiency

“…In any case this behavior is present also in the measurements taken on the PA2 stand-alone (see), consequently can't be attribute to mutual interaction between the two PAs. This behavior, along with the difference in gain, estimated in 2.5 dB from suggested the use of a digital predistortion unit in order have a sufficient linearity; this unit was implemented adopting the same architecture used in [3]. The resulting look-up-table for the two states suitable to linearize the entire system, thus taking into account also the SPDT nonlinearities as well as the interaction of the two PAs, are reported in Fig.…”

“…When "on" they singularly operate as a class-AB amplifier, while when "off" they are seen as a parasitic load in parallel to the base and to the collector of the active HBT section. The PA schematic is reported in Fig.1, the detailed description of this circuit is given in [3]. The number of "on" transistors is adjusted in response to changes in the required instantaneous output power, while the collector current density is kept constant to maintain the power gain constant in each rHBT state.…”

“…Power supply control schemes offer the greatest potential of high average efficiency operation for high PAR signals [2]. In [3] we investigate experimentally the capability of a class-AB PA based on a reconfigurable HBT in SiGe technology suitable for step envelope tracking architecture, where the dynamic power control was performed at the envelope domain.…”