Multi-mode sub-Nyquist rate digital-to-analog conversion for direct waveform synthesis

This paper describes the sub-Nyquist rate digital-to-analog conversion technique for a direct waveform synthesis (DWS) transmitter. IEEE 802.22 TV band Cognitive Radio (CR) transmitter requires seamless frequency hoping and wide frequency coverage of 54 MHz-806 MHz. The proposed transmitter directly converts the digital baseband samples to RF frequencies in the target channels obviating the up-conversion mixer. The mostly-digital architecture of this transmitter features agile functionality support for Software Defined Radio (SDR) operation. A 10-bit 600-MS/s multi-mode DAC shapes the analog output spectrum envelope to enhance image spectrum located in the target channels and suppress other unwanted harmonics. Compared to Nyquist rate direct synthesis, this sub-Nyquist rate DWS architecture reduces both system complexity and power consumption by half.