A novel digital-intensive hybrid transmitter (TX) architecture is presented, combining conventional inphase and quadrature (I/Q) with constrained phase modulation. The proposed architecture utilizes an RF-DAC with phase modulated RF clock and adjusted I/Q components. By incorporating phase modulation the quadrature component is kept small while the inphase component approaches the complex signal envelope. Compared to a digital-quadrature TX architecture this results in a significantly reduced average and peak RF-DAC cell utilization. Therefore, the RF-DAC can be operated in less backoff at higher average output power and drain efficiency. The phase modulation is constrained in order to relax the phase modulators system requirements. Compared to a digital polar TX architecture utilizing an RF digital phase-locked loop with two-point phase modulation, this results in reduced frequency modulation and digital-controlled oscillator tuning range requirements. In addition, the design effort is further shifted from analog to digital domain in order to better exploit the benefits of CMOS technology scaling. Index Terms-Wireless communication, digital polar transmitter, digital quadrature transmitter, hybrid polar-I/Q transmitter, phase modulation, quadrature modulation, RF digital-to-analog converter (RF-DAC), RF digital power amplifier (RF-DPA), RF digital phase-locked loop (RF-DPLL). I. INTRODUCTION W IRELESS transceivers for multi-band, multi-standard mobile handset applications operating in the sub-6 GHz range are usually implemented in ultra-deep

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