A 1.6-GS/s 12-bit return-to-zero GaAs RF DAC for multiple Nyquist operation

A 12-bit 1.6-GS/s digital-to-analog converter (DAC) implemented with 4-μm² GaAs HBT process is presented. Return-to-zero (RZ) current switches are added to current steering DAC for high-frequency wideband applications to achieve 800-MHz bandwidth at first and second Nyquist band without the need for a reverse sinc equalization filter in wideband transmitter application. The RZ circuit also improves spectral purity by screening the switching noise from the analog output during data transition. Measured performance shows two-tone third-order harmonic distortion of -70 dB at 1.5-GHz output frequency, clocked at 1.6 GHz. Reliable interface with CMOS logic IC is guaranteed with the inclusion of a four-clock-deep FIFO circuit. The DAC dissipates 1.2 W at -5 V when sampled with 1.6-GHz clock, with typical output voltage swing of 1.2 V_PP.