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 $2.4 \times$ and the symbol error rate (SER) by $4.5 \times$, demonstrating its suitability for high-efficiency and reliable signal transmission.