We propose to develop the “Hoku ASIC”, a mixed-signal integrated circuit designed using a new method we call Element Level Adjustability (ELA). Most radiation robust mixed-signal integrated circuits utilize specific CMOS technologies and substrate strapping layout techniques to achieve high degrees of radiation robustness. In a mixed-signal IC, each of the transistors in the circuit play a specific role. The IC becomes dysfunctional after radiation exposure when the characteristics of one or more of the transistors changes and the affected transistors are no longer able to perform their intended role in the circuit at the intended level of performance. As a result, the circuit fails one or more specs. With autonomous ELA, each transistor may be isolated and tested during a calibration routine. If the transistor fails a designated test, its size (effective W/L) or bias condition can be modified until it is able to perform its intended role. By performing these calibrations during calibration periods and self-correcting the circuit as it is exposed to radiation, the resulting circuit can potentially function with a higher dose of radiation than otherwise possible without ELA.
Architecture, choice of technology, and transistor layout structure are elements that have been studied and compared for radiation robustness. We are developing a new general approach that may be suitable for improving the radiation hardness using a number of architectures, can be applied to any CMOS technology, and can be better suited to conventional layout techniques due to the higher density achievable as compared with ELT transistors. In the solicitation, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), charge-sensitive amplifiers, and readout integrated circuits for photomultipliers are identified as demonstration vehicles. In this proposal, we gear our description to ADCs but the concepts may be applied to other analog circuit blocks called out in the solicitation.
Our new method of ELA will be able to be applied to any analog or mixed-signal IC resulting in improved radiation hardness for a wide variety of applications required in space vehicles and their payloads. Our approach exploits the ease with which basic microprocessors can be implemented on ICs providing control, and the high transistor density allowed in even non-leading edge CMOS technologies.
Our new method of ELA will be able to be applied to any analog or mixed-signal IC resulting in improved radiation hardness for the large number of applications and environments where radiation-tolerant and/or radiation-resistant analog or mixed-signal ICs are required. Our approach develops design principles which can be exploited in even non-leading edge CMOS technologies.