Rafael Galhardo Vaz

TID in Flash-Based FPGA: Power Supply-Current Rise and Logic Function Mapping Effects in Propagation-Delay Degradation

We exposed a flash-based FPGA to radiation to measure variations in current, temperature, propagation-delay and duty-cycle in logic circuits. Propagation-delay degradations vary from 400% to 1100% before functional failure, according to circuit and logical mapping. Electrical simulations are carried out to study the difference of behavior in the degradation of different logic mappings.

TID in a Switched-Capacitor FPAA: Degradation and Partial Inactivity Windows Due to Compensating Effects in MOS Transistors

Results of irradiation experiments on a 0.6 μm switched-capacitor analog array indicate a sudden recovery of the FPAA performance degradation during the irradiation phase. The main parameter considered to check the performance of the device is the total harmonic distortion of the processed analog signals. The observed recovery is associated with the compensating effects of oxide and interface trapped charge in the NMOS transistors of the array in a particular window of the accumulated dose received by the device. Experimental results are discussed and simulations performed to confirm the hypotheses for the observed phenomenon.

Soft error rate in SRAM-based FPGAs under neutron-induced and TID effects

This paper presents new experimental results about the sensitivity of an SRAM-based FPGA under neutron-induced and total ionizing dose effects. Both effects are combined in a practical experiment composed of a set of eight isotropic emission material blocks for neutron irradiation and a gamma rays source for ionizing dose. The experiment was performed at Instituto de Estudos Avançados, São José dos Campos, Brazil. The soft error rate has been measured from counting the bit-flip rate of the configuration memory bits and the errors at the output of the design application. Current results have shown that the soft error rate increases under neutrons when the accumulation of ionizing radiation in the device also increases until the observed doses.

Influence of Alternate Biasing on TID Effects of Irradiated Mixed-Signal Programmable Arrays

This work investigates the influence of alternate biasing on TID effects in mixed-signal programmable devices. By reducing the time the device is biased when exposed to ionizing radiation, the severity of TID effects is also reduced, due to the increasing in the initial recombination of electron-hole pairs and the radiation induced charge neutralization effect. These effects are investigated considering a switched capacitor filter prototyped in a Field Programmable Analog Array. Eight samples of such device were exposed to gamma radiation while the devices were alternately biased, by repeatedly turning the power on and off, corresponding to different equivalent total biasing times and duty-cycles. Results show increase in radiation tolerance to the alternate biased devices, which is dependent also on the biasing duty-cycle. Considering this behavior, a novel system level radiation hardening technique, based on modular redundancy, associated to an alternate biasing scheme, is also proposed in this paper.

Impact of TID-induced threshold deviations in analog building-blocks of operational amplifiers

This paper presents an investigation on the performance of analog building-blocks of two counterpart architectures of Operational Amplifiers (with PMOS and NMOS differential amplifier as input stage) under cumulative radiation effects. This investigation is performed through Spice simulations, by injecting typical radiation-induced shifts in the threshold voltage of the transistors for the considered technology, a 0.5 µm standard CMOS process. Transient and DC (Direct Current) analysis are performed in differential and inverter stages of a simple two-stage operational amplifier. The linearity and voltage swing of both amplifier stages are evaluated, as well as, the effects on the bias current and the output offset voltage. Simulation results show that the NMOS differential amplifier architecture may have an improved robustness in radiation environments, if compared to its PMOS counterpart, when considering the typical behavior of MOS transistors under radiation.

Alternate Biasing Modular Redundancy: An alternative tolerance technique to cope with TID effects

In this work a novel radiation tolerance technique based on modular redundancy, associated to an alternated biasing scheme, is presented. The goal of this technique is to extend electronic systems lifetime in radiation environments for circuits that are susceptible to TID effects. In order to validate this technique, a board level prototype was built, considering an FPAA (Field Programmable Analog Array) as Device Under Test (DUT), to which the concept was applied. The prototype was exposed to Co60 gamma radiation with a dose rate of 1 krad(Si)/h. Results show that devices that are alternated biased are able to tolerate higher accumulated doses than the one that is permanently biased.

Evaluation of a mixed-signal design diversity system under radiation effects

In this work a data acquisition system, based on a design diversity redundant scheme, is tested under total ionizing dose effects. The data acquisition system is composed by three ADCs and two voters, implementing different levels of diversity (architectural and temporal). This system is implemented on a 130nm commercial mixed-signal programmable SoC (PSoC 5), from Cypress Semiconductor. The system was tested under 60Co gamma radiation with a dose rate of 1 krad(Si)/h reaching a total dose of 242 krad(Si). One of the system copies presented a significant degradation on its linearity during the irradiation, while the others kept the functionality with less severe degradation, evidencing the advantage of using diversity to improve resilience in mixed-signal redundant systems.

Measurements of radiation effects on a 4 Mb PSRAM memory

The results of a static test of total ionizing dose (TID) effects on an ISSI 4Mb PSRAM memory are reported in this work. The irradiation was performed at the IEAv’s Laboratory of Ionizing Radiation with 1.17 and 1.32 MeV gamma-rays from a 60Co source at a dose rate of 2.5 krad/h up to an accumulated dose of 215.7 krad. The TID threshold for bit flip found in this experiment was 52.5 krad. From a sampling of 4096 memory addresses it was estimated a bit flip rate of approximately 50% at an accumulated dose of 215.7 krad.

The prototype of a detector for monitoring the cosmic radiation neutron flux on ground

This work presents a comparison between the results of experimental tests and Monte Carlo simulations of the efficiency of a detector prototype for on-ground monitoring the cosmic radiation neutron flux. The experimental tests were made using one conventional 241Am-Be neutron source in several incidence angles and the results were compared to that ones obtained with a Monte Carlo simulation made with MCNPX Code.