The figure below shows the 𝑖𝑡ℎ full-adder block of a binary adder circuit. Ci is the input carry and Ci+1 is the output carry of the circuit. Assume that

Q. The figure below shows the 𝑖^𝑡ℎ full-adder block of a binary adder circuit. Ci is the input carry and Ci+1 is the output carry of the circuit. Assume that each logic gate has a delay of 2 nanosecond, with no additional time delay due to the interconnecting wires. If the inputs Ai , Bi are available and stable throughout the carry propagation, the maximum time taken for an input Ci to produce a steady-state output Ci+1 is _____nanosecond.

Sol:

Given that Ai and Bi are available throughout the carry propagation. The maximum time taken for an input C1 to produce a steady state output C_i+1 involves two gates as shown in figure. Each gate has a delay of 2ns Total time delay = 4 ns.