Gill 1 MAPLD 2005/234 Analysis and Reduction Soft Delay Errors in CMOS Circuits Balkaran Gill, Chris Papachristou, and Francis Wolff Department of Electrical Engineering and Computer Science. Case Western Reserve University Cleveland Ohio USA

2 Gill MAPLD 2005/234 Outline Introduction. Soft delay phenomenon. Soft delay modeling. Soft delay error analysis and reduction technique in combinational circuits. Future work and conclusion.

3 Gill MAPLD 2005/234 Introduction Single Event Upsets (SEUs) are due to high energy particle strikes at sensitive nodes in CMOS circuits. These upsets originate from cosmic rays in outer space and α-particles within the chip. Soft Error Rate (SER) in CMOS circuits is projected to increase as the process technology scales down.

4 Gill MAPLD 2005/234 Introduction (cont’d) A particle strike at the sensitive nodes of combinational circuits results in a glitch (pulse) which can propagate to the circuit output and captured by output flip-flops. A particle strike at the sensitive node during the signal transition can result in temporary delay (soft delay) which can violate the circuit timing. SEUs in memory cause temporary cell flip. Semiconductor memories are more vulnerable than logic.

5 Gill MAPLD 2005/234 Soft Delay Phenomenon When a particle strike occurs during the transition at a node, it can introduce additional temporary delay.

6 Gill MAPLD 2005/234 Soft Delay Propagation Propagation of the soft delay.

7 Gill MAPLD 2005/234 Soft Delay Propagation The pulse generated due to the particle strike during the transition attenuates resulting in soft delay. Soft Delay Error

8 Gill MAPLD 2005/234 Soft Delay Modeling Mixed-mode simulations: Circuit and Device Simulations.

9 Gill MAPLD 2005/234 Device simulations for Soft Delay Particle strike simulations using photo- generation models in DAVINCI.

10 Gill MAPLD 2005/234 Current Pulse Extraction Extracted current pulses for various energies of the hitting particle.

11 Gill MAPLD 2005/234 Soft Delay in ISCAS85 Benchmark Circuits Soft delay at the critical path of ISCAS85 circuits for various hitting particle energies.

12 Gill MAPLD 2005/234 Soft Delay Error Analysis and Mitigation Flow

13 Gill MAPLD 2005/234 Reducing SDE - Example

14 Gill MAPLD 2005/234 Conclusion Found Soft Delay problem and developed models to analyze its effects. Verification of the soft delay using mixed- mode simulations. Characterization of the soft delay in ISCAS85 circuits. Soft delay error analysis and mitigation technique.

15 Gill MAPLD 2005/234 Current and Future Work Current work Soft delay error analysis approach for large circuits. Soft errors analysis in reconfigurable system (FPGA). Future work System level node sensitivity analysis approach. Mitigation techniques for soft errors in VLSI circuits. Mitigation techniques for soft errors in SRAM.