6

Conclusions Part I

In Chapter 2 models of metastability in a latch are described which enable an estimate of the MTBF of a synchronizer to be made

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and the shape of a typical histogram of events against synchronization time to be predicted,

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Refinements to the model also allow effects in the deterministic region, and after the back edge of the clock to be estimated.

Chapter 3 describes metastability in simple NAND gate latch circuits, how the nonstandard levels characteristic of metastability can be filtered out, and the design of commonly used synchronizer flip-flops such as the Jamb latch. Versions of the Jamb latch can be designed which show better performance, or are more robust towards supply voltage, process and temperature variation. Circuits useful in asynchronous situations, where metastability may also occur, are the MUTEX and the Q-flop.

In Chapter 4 the noise level in a latch is shown both theoretically and experimentally to be approximately:

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In a normal system where the probability of all time differences between data and clock signals is constant, noise has little effect on synchronization times, however in the case of a malicious input, it reduces the probability ...

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