A digitally modulated mm-Wave cartesian beamforming transmitter with quadrature spatial combining

With fast-growing demand for high-speed mobile communications and highly saturated spectral usage below 10GHz, mm-Wave frequency bands are emerging as the key playground for future high-data-rate wireless standards. Recent years have witnessed vast technology development on V-band (60GHz) Wireless Personal Area Networks (WPAN) and E-band (80GHz) point-to-point cellular backhauls. However, existing integrated CMOS mm-Wave solutions have relatively poor energy efficiency, especially for the transmitter (TX). This is mainly due to the use of traditional Class-A Power Amplifiers (PAs) that provide good linearity but suffer from low efficiency. In addition, the efficiency of Class-A PAs drop dramatically at power back-offs, making these transmitters even less efficient when conveying non-constant envelope signals. State-of-the-art mm-Wave Class-A PAs show less than 5% efficiency at 6dB back-off [1,2].