Systematic Design-for-Reliability in mixed signal circuits

Design for Reliability (DFR) ensures a system or component functions correctly for a specified time under stressed conditions. Reliability of analog circuits is usually achieved by off-line testing, calibration, and/or minimal repairs. But fault tolerance for transient faults is becoming necessary for analog and mixed signal circuits. Reliability in applications, like, avionics, space and automobiles is of greater concern now since they can fail due to transient faults under external radiation.;A lot of work and effort has been put on digital blocks in the past to make them fault tolerant. But nothing substantial has been done for analog or mixed signal blocks. Also, not very accurate fault models exist for analog and mixed signal blocks. We will survey literature for existing DFR approaches.;We propose a redundancy based fault-tolerant methodology to design a highly reliable analog/ digital circuits and systems. The key contribution of our work is an innovative mean voter. This mean voter is a low power, small area, very high bandwidth and linearly scalable unit. Our mean voter works for both odd and even N for analog units and hence reduces the area and power further.;We also propose a method of identifying critical nodes in analog blocks. These nodes have the high impedance characteristics and contribute to the gain and dominant poles in the circuit. Number of high impedance nodes in a block are used in the simulation process to determine the redundancy factor N to be used.;For the proof of concept, we designed two fault tolerant analog circuits, i.e. a low pass anti-aliasing analog filter and a 4-bit flash ADC. We also presented fault-tolerance mechanism in 4-bit binary adder and an FPGA cell for demonstrating its application and advantage in digital applications. Experimental results are reported to verify the concepts and measure the system's reliability when failures, such as single upset transient faults occur.;Keywords : Design for Reliability, fault-tolerance, redundancy, reliability, single upset transient, transient faults, voter, yield.