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We are given the combinational circuit shown
here consisting of an inverter, an AND gate,

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an exclusive OR gate, and a multiplexor.

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We are also provided with the contamination
and propagation delays for each of the components

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in the circuit.

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We are then asked to determine the contamination
delay and propagation delay for the entire

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circuit.

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The propagation delay of a circuit is defined
as the longest delay that can occur from when

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the inputs changed to when the output becomes
stable.

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In order to calculate the propagation delay
of a circuit, we need to identify the path

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from input to output whose sum of the propagation
delays is the largest.

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For this circuit, the longest delay path is
through the exclusive or gate and the multiplexor.

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The sum of the propagation delay across these
2 gates is 2.1 + 1.5 = 3.6 ns.

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The contamination delay of a circuit is defined
as the shortest delay from when the inputs

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change to when the outputs begin to change,
or when the outputs are no longer guaranteed

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to be holding their previous stable value.

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In order to calculate the contamination delay,
we find the path whose sum of the contamination

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delays is the least.

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For this circuit, the shortest path is from
input A through the selector of the multiplexor.

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So the contamination delay for this circuit
is equal to the contamination delay of the

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multiplexor which equals 0.2 ns.