Undersampling Observation-Based Compact Digital Predistortion for Single-Chain Multiband and Wideband Direct-to-RF Transmitter

Modern wireless network operators are consistently looking for improvements in the wireless access infrastructure that minimize size, weight, and power. Therefore, compact multiband RF and wideband RF solutions offer an attractive role in forthcoming fifth generation networks. This paper presents a novel compact wideband RF transmitter architecture that is based upon an undersampled digital predistortion (DPD) methodology. The proposed architecture minimizes the required number of RF/analog components in the system by using RF-DAC-based direct RF sampling at the forward transmitter data path and one undersampled analog-to-digital conversion (ADC) with certain bandpass filters at the DPD sampling receiver path. Extensive experimental results validate that the DPD-enabled RF transmitter bandwidth can be significantly increased using the proposed multirate track-and-hold amplifiers architecture. Experimental tests achieved multiple GHz DPD bandwidths with satisfactory linearization performance via very compact sampling receiver that has one undersampled ADC. Particularly, we evaluated three application scenarios: 1) three-band carrier aggregated LTE signals (each one occupying 20-MHz instantaneous bandwidth), the linearization performance achieved 50-dBc adjacent channel power ratio (ACPR) with more than 1-GHz bandwidth using ADC running at 76.8 and 61.44 MSPS; 2) single-band LTE signal with continuous 100-MHz instantaneous bandwidth, the linearization performance achieved -48-dBc ACPR using 61.44-MSPS ADC; and 3) single-band LTE signal with continuous 20-MHz bandwidth at 4 GHz, the linearization performance achieved -54-dBc ACPR using 61.44-MSPS ADC.