Metastability,MTBF,synchronizer & synchronizer failure
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This document discusses metastability, mean time between failures (MTBF), synchronizers, and synchronizer failures. It begins with introductions to metastability and cases where it can occur. It then illustrates metastability with diagrams and graphs. It discusses how systems enter metastability and what occurs during metastability. The document derives the MTBF equation and provides an example calculation. It concludes by listing references for further information.
Metastability,MTBF,synchronizer & synchronizer failure
- 1. METASTABILITY ,MTBF, SYNCHRONIZER & SYNCHRONIZER FAILURE PRESENTED BY : SUNIL KUMAR (IMI2012001) : VERSHA VARSHNEY(IMI2012010) : VIBHOR GUPTA (IMI2012020)
- 2. CONTENTS 1. INTRODUCTION 2. CASES OF METASTABILITY 3. ILLUSTRATION OF METASTABILITY 4. ENTERING METASTABILITY 5. DURING METASTABILITY 6. INTRODUCTION TO MTBF 7. DERIVATION OF MTBF 8. REFERENCES
- 3. WHAT IS METASTABILTY Whenever there are setup and hold time violations in any flip-flop, it enters in a state where its output is unpredictable At the end of metastable state, the flip-flop settles down to either '1' or '0'.
- 4. CASES OF METASTABILITY • FOR SYNCHRONOUS SYSTEM- When skew is present • FOR ASYNCHRONOUS SYSEM- Whenever setup and hold time violation occurs.
- 6. ENTERING METASTABILITY Fig:2.Flip –Flops, with four gate delays from D to Q.
- 7. GRAPH B/W INPUT VOLTAGE AND TIME Figure 2 :Charts show multiple inputs D, internal clock (CLK2) and multiple corresponding outputs Q (voltage vs. time). The input edge is moved in steps of 100ps, 1ps and 0.1fs in the top, middle and bottom
- 8. From the graph if we increase the frequency of input signal then the probability of system to move in metastability will increase period of metastability also increased
- 9. DURING METASTABILITY Fig.3 Analog model of a metastable latch
- 10. •The Analog model result in two first- order differential equations that can be combined into one, as follows:-
- 11. INTRODUCTION TO MTBF MTBF is Mean time between failure It gives us information on how often a particular element will fail. It gives the average time interval between two successive failures.
- 12. EQUATION OF MTBF The MTBF equation is MTBF = Where: S = synchronization period Tw, = flip-flop characteristic constants FC= clock frequency FD = average input rate of change
- 13. DERIVING MTBF EQUATION Clearly, if meta-stability starts with V=VO and ends when V=V1, then the time to exit meta- stability is tm:
- 14. Probabilistic analysis shows that, given the fact that a latch is metastable at time zero, the probability that it will remain metastable at time t >0 is e- t/τ, which diminishes exponentially fast. The probability of entering metastability, which is the probability of D‟s having changed within the TW window, is TW/TC =TWFC But D may not change every cycle; if it changes at a rate FD, then the rate of entering metastability becomes Rate =FDFCTW.
- 15. P(failure) = p(enter MS) X p(time to exit > S) = X Rate(failures) = X The inverse of the failure rate is the mean time between failures (MTBF): MTBF =
- 16. MTBF EXAMPLE Consider an ASIC designed for a 28-nm high- performance CMOS process. We estimate t = 10 ps, TW = 20 ps and FC = 1 GHz. Let’s assume that data changes every 10 clock cycles at the input of our flip-flop, and we allocate one clock cycle for resolution: S = TC. Plug all these into the formula and we obtain 4 X 1029 years.
- 17. REFERENCES R. Ginosar, “Metastability and synchronizers:A tutorial,” IEEE Design Test Comput., vol. 28, pp. 23–35, May 2011. S. Lubkin, „„Asynchronous Signals in Digital Computers,‟‟ Mathematical Tables and Other Aids to Computation (ACM section), vol. 6, no. 40, 1952, pp. 238-241. H.J.M. Veendrick, „„The Behavior of Flip-Flops Used as Synchronizers and Prediction of Their Failure Rate,‟‟ IEEE J. Solid-State Circuits, vol. 15, no. 2, 1980, pp. 169-176.
- 18. THANKYOU