Wideband Linearization of a Carrier Aggregation Transmitter Using Analog Signal Injection and 2-D Digital Predistortion

Abstract

We introduce a transmitter (TX) architecture and a linearization technique for concurrent transmission of two intraband noncontiguous carrier aggregation signals in the 5 GHz frequency band. The technique is based on low-power and narrowband analog signal injection to compensate for out-of-band (OOB) third-order intermodulation distortions (IMD3), together with 2-D digital predistortion to address error vector magnitude (EVM) degradation caused by in-band intermodulation and cross-modulation distortions. The hybrid analog-digital design enables wideband linearization over the entire third-order distortion bandwidth (BW) using practical sampling rate requirements from the digital-to-analog converter (DAC) and analog-to-digital converter (ADC). The system’s performance was evaluated using a class AB power amplifier implemented in the 180 nm CMOS technology and two VHT 802.11ac Wi-Fi signals with a 20 MHz modulation BW. The linearization technique achieves 7–12 dB cancellation of OOB IMD3 products along with 6–9 dB of in-band EVM correction at 8 dBm average output power over a BW of up to 1.2 GHz, with only 60 MHz BW requirement from the DACs and ADCs.