A 10-Bit, 600 MS/s Multi-Mode Direct-Sampling DAC-Based Transmitter

This paper presents a 10-bit, 600 MS/s direct-sampling sub-Nyquist rate DAC-based frequency-agile wideband transmitter for IEEE 802.22 cognitive radio applications in the VHF/UHF TV band (54 – 862 MHz). Multi-mode reconstruction using Gilbert cells, including non-return-to-zero, return-to-complement, and return-to-complement with reset, allows the DAC to utilize the image spectrum in the higher Nyquist zones for wideband direct synthesis. A two-dimensional decoder of the dynamic element matching is applied to reduce the correlated noise to the input signals. A multi-mode control signal generator uses a slack borrowing strategy to provide the transmitter’s zero frequency hopping time without interference between the three modes to improve the quality of service of the cognitive radio system. A low-power supply-regulated PLL and a divided-by-2 circuit generates quadrature DAC sampling clock signals of 600 MHz to ensure a SDR of > 70dB. The proposed transmitter is fabricated in 65 nm CMOS within an active area of 0.3 mm2, and it achieves a DNL of 0.12 LSB, an INL of 0.25 LSB, an SFDR of > 57 dBc, and IM3 of < −62 dBc in the TV band while consuming 19 mW.