Ben Bitdiddle invents a new and improved synchronizer in Figure 3.76 that he claims eliminates metastability in a single cycle. He explains that the circuit in box M is an analog “metastability detector” that produces a HIGH output if the input voltage is in the forbidden zone between V_IL and V_IH. The metastability detector checks to determine whether the first flip-flop has produced a metastable output on D2. If so, it asynchronously resets the flip-flop to produce a good 0 at D2. The second flip-flop then samples D2, always producing a valid logic level on Q. Alyssa P. Hacker tells Ben that there must be a bug in the circuit, because eliminating metastability is just as impossible as building a perpetual motion machine. Who is right? Explain, showing Ben’s error or showing why Alyssa is wrong.

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CLK CLK D2 D-