Cryogenic Evaluation of a Digital-to-Analog Converter for a Trapped-Ion Quantum Computer

This article presents a digital-to-analog converter (DAC) for shuttling operations in a trapped-ion quantum computer (TIQC) measured at 4.6 K. We provide an extensive analysis and comparison of measured characteristics at room temperature (RT) versus those at cryogenic temperature (CT), particularly focusing on the DAC’s static and dynamic behavior, as well as its noise performance. By making well-conceived analytical design choices, we show that the DAC’s performance at CT can match its performance at RT. This is achieved through sufficient design margins, the selection of suitable components, and the adjustment of biasing voltages. The investigated chip features a 12 bit, resistive R-2R ladder-based DAC, which also comprises an input buffer for the DAC’s reference voltage and a simplistic SPI to read the digital control words. Implemented in Infineon’s 130-nm bipolar-CMOS-DMOS (BCD) technology, the DAC consumes 1.1 mW from a 1.5 V power supply at RT. Its power consumption increases to around 1.5 mW at CT due to necessary biasing adjustments. The DAC’s linearity, characterized by its differential-nonlinearity (DNL) and integral-nonlinearity (INL), remains almost unchanged across temperatures, aligning with its spurious-free dynamic range (SFDR). The slew-rate (SR) decreases toward CT compared to RT. While the thermal noise floor also decreases, the low-frequency noise increases at CT. Overall, this leads to a slight decrease in the DAC’s noise performance at 4.6 K.