A Self-Calibrated Cryogenic Current Cell for 4.2 K Current Steering D/A Converters

This brief presents a cryogenic CMOS unit current cell operating from room temperature down to 4.2 K, and it is primarily designed for low temperature current steering (CS) D/A converters (DACs). A novel structure along with an analog calibration technique is proposed in designing the cell that helps it to overcome low temperature induced nonlinear and mismatch effects. Due to the flexible configuration of the cell architecture, it can be used in both LSB and MSB parts of a partially-segmented CS DAC. The current cell retains its 4-bit precision level from 300 K down to 4.2 K, and drives a 50 Omega load to 6.8 mV in 600 ps rise time. A 6-bit converter utilizing the cell achieves differential and integral nonlinearity of 0.17 LSB and 0.33 LSB, respectively, while its average power consumption is <3.2 mW from a 3 V power supply. It is fabricated using a commercial 0.5 mu m single poly three metal silicon-on-sapphire CMOS process.