This radiation-hardened, compact, low-power, quad 12-bit digital-to-analog converter (DAC) application specific integrated circuit (ASIC) incorporates science-driven features based on applications in a realistic space environment such as threshold setting, current bias circuits, and general-purpose DC voltage generation. It is based on a previous 10-bit DAC that exhibited excellent test results, presenting the possibility of a 12-bit design.

Figure 1. RHDAC12 packaged in 16-lead ceramic SOIC.
The RH-DAC12 addresses the need for spaceworthy, multi-channel data converters to reduce the size, mass, and power of instrument electronics. The main objective was to design, fabricate, and test such an ASIC that will enable and advance miniaturized instrument electronics. The development includes design and fabrication of prototype chips in a commercial CMOS (complementary metal-oxide semiconductor) process.

Figure 2. RH-DAC12 die photo.
Features include triple voted registers to mitigate single event upsets (SEUs), 500 krad total ionizing dose (TID) and single-event-latchup (SEL) linear energy transfer (LET) of 130 MeV cm2/mg, single-event-upset (SEU) LET of 104 MeV cm2/mg, single 3.3 V supply, pin-selectable I2C or SPI interface, monotonic design (no missing codes), wire bonding selectable outputs (unbuffered for capacitive loads, buffered for resistive loads, and buffered for large capacitive loads), output rail-to-rail input/output amplifier that can drive resistive loads down to 1 kilohm, and internal buffer/amplifier for top reference voltage. The ASIC accommodates multiple space-worthy packaging configurations such as 24/20/16-lead ceramic SOIC (small outline integrated circuit), and ceramic flatpack. Bias pins can be used to adjust OPAMP/OTA quiescent current.

The RH-DAC12 ASIC pushes the envelope of currently available space-worthy devices. A selectable serial interface (I2C or SPI) is particularly attractive, as it reduces wiring complexity and mass, particularly when distributing multiple devices across an instrument or system. To provide a point of comparison, the RHDAC12 device contains four channels with a footprint comparable to available single-channel radiation-hardened devices, greatly reducing the number of components and size, weight, and power (SWaP).

This work was done by George Suarez, Jeffrey DuMonthier, and Nikolaos Paschalidis of Goddard Space Flight Center. GSC-16989-1


NASA Tech Briefs Magazine

This article first appeared in the December, 2015 issue of NASA Tech Briefs Magazine.

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