Analysis and Design of High-Order QAM Direct-Modulation Transmitter for High-Speed Point-to-Point mm-Wave Wireless Links

A novel high-speed wireless transmitter (TX) architecture is presented that directly transforms incoming data bits into high-order 4
^M
-quadrature amplitude modulation (QAM) constellation by adding multiple quadrature phase shift keying (QPSK) signals with appropriate amplitude ratios. The costly high-speed digital-to-analog converters (DACs) in conventional TXs are thus completely avoided, resulting in a highly integrated solution amenable to ultra-high speeds and operating frequencies. Design tradeoffs are analyzed in detail. Based on this article, a TX prototype at 115-GHz carrier frequency implementing the 16QAM direct-modulation scheme is fabricated in a 180-nm SiGe BiCMOS process (f
_MAX
= 270 GHz). Wireless testing at a 20-cm distance with 25-dBi horn antennas on both transmitting and receiving side measures 20-Gb/s data rate with an error vector magnitude (EVM) of -15.8 dB and modulated output power of +1 dBm. The TX consumes 520 mW of power and occupies 3.17 mm
²
of active area.