A Fully Integrated Optimal Modulation Bits-to-RF Digital Transmitter Using Time-Interleaved Multi-Subharmonic-Switching DPA

A fully integrated bits-to-RF transmitter featuring deep power back-off (PBO) enhancements is demonstrated, incorporating a time-interleaved multi-subharmonic-switching digital power amplifier (DPA) and a harmonic-rejection digital-to-phase converter (DPC). This architecture also employs a non-uniform Optimal Modulation (OM) constellation to enhance the transmission error rate. The system implemented in 65 nm CMOS achieves 58.1% peak power-added efficiency (PAE) and 52% peak system efficiency (SE) with 22.7 dBm peak output power, using 2.6 and 1.3 V VDDs. Dynamic measurements of a 64-point OM constellation achieved 23.1% PAE and 19.4% SE at 16.9 dBm average output power, while maintaining an EVM of -29.9 dB at 1.5 GHz carrier frequency. Compared to standard QAM, the proposed OM scheme reduces the bit error rate (BER) by 2.4× and the symbol error rate (SER) by 4.5×, demonstrating its suitability for high-efficiency and reliable signal transmission.