A 28 GHz Single-Input Linear Chireix (SILC) Power Amplifier in 130 nm SiGe Technology

This article presents an integrated high-efficiency 28 GHz power amplifier (PA) employing a combination of Chireix outphasing and Doherty architectures in order to simultaneously achieve power back-off efficiency and linearity with a single RF input signal and no predistortion. The amplifier consists of a dual-input high-efficiency outphasing PA and a simple input network which serves as a power splitter and feeds the same signal to the inputs of the main and auxiliary PA cells that are biased in class-AB and class-C regions, respectively, similar to the Doherty architecture. The operation of the PA cells together with the Chireix combiner result in back-off efficiency enhancement plus systematic AM-AM and AM-PM variations which are used to correct the distortions caused by transistors, resulting in a linear response. The implemented PA demonstrates 19 dBm saturation power (Psat) with 34.4% peak power-added efficiency (PAE) and 6 dB back-off PAE of >23% at 27.5 GHz. The modulated signal performance using a 100 MHz 64QAM OFDM signal shows an average output power of 11.9 dBm with PAE >20%, EVM < 5%, and ACLR < -33 dBc without using predistortion.