Odair Lelis Goncalez

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.

Analyzing the Effects of TID in an Embedded System Running in a Flash-Based FPGA

This work analyzes the behavior of a designed embedded system composed of microprocessor, memories and SpaceWire (SpW) links under Total Ionizing Dose (TID) synthesized into a commercial flash-based FPGA from Actel. Two tests were performed: one the FPGA is configured just once at the beginning of the irradiation and the other the FPGA is reconfigured every 5 krad (Si). Results evaluate power supply current (Icc), temperature, function operation and performance degradation.

Investigating the effects of transient faults in Programmable Capacitor Arrays

In this work, the effects of transient faults in Programmable Capacitor Arrays (PCA) are investigated. Usually, PCA architectures are built from a set of binary-weighted capacitor branches, which can be connected in parallel. The connection of each branch to the terminals of the capacitor array is programmed through analog switches (usually transmission gates). Transient faults, potentially caused by radiation interaction with the silicon, or by the impact of strongly ionizing particles in sensitive nodes, may temporarily close a switch in the PCA, whose default state should be open. In this case, it may occur a charge sharing process, from the equivalent capacitor (programmed into the PCA) to the temporarily connected capacitor (due to the transient effect). Therefore, after the transient, the voltage stored in the equivalent capacitor may be reduced. This effect is investigated with spice simulations. The influence of the values of the capacitors and the sizing of the analog switches (and its control logic) in the magnitude of the charge sharing effect is also investigated. Finally, some possible design-level mitigation techniques are discussed.

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.

TID in a Mixed-Signal System-on-Chip: Analog Components Analysis and Clock Frequency Influence in Propagation-Delay Degradation

We exposed a mixed-signal system-on-chip to gamma radiation in order to measure variations in current, temperature and propagation-delay in its components, such as configurable array, embedded analog blocks and microprocessor.

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.

Total Dose Effects on Voltage References in 130-nm CMOS Technology

This paper investigates the impact of total ionizing dose (TID) effects on the performance of CMOS voltage reference circuits. Four circuits were designed using a commercial 130-nm CMOS process and without any radiation-hardening technique. Two of the designed circuits generate the output voltage proportional to the bandgap voltage, while the other two generate the output voltage proportional to the MOS threshold voltage. The measured output voltage variation caused by TID was from 1% to 15% for a total dose of up to 500 krad, depending on the circuit topology. The leakage currents induced by radiation in MOS transistors and diodes were the main cause of output voltage variation.