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**2x2 bit Multiplier**

i build a 2x2 bit multiplier circuit where i take a number (a1a0) and multiply it by (b1b0) . and im asked to calculate the time propagation from high to low , and from low to high for every input to every output . for example :

Tp(HL): a0 -> q0 = ?

a1 -> q0 = ?

b0 -> q0 = ?

b1 -> q0 = ?

Tp(LH): a0 -> q0 = ?

a1 -> q0 = ?

b0 -> q0 = ?

b1 -> q0 = ?

and so on and on for every output .

I'm having problem figuring out the time because there more than one possibilities for inputs. and for the output to change from low to high for example , the inputs have to be related in a way to guarantee that the output changes from 0 to 1 . but at the same time there are more than one possibility for different inputs . so how can i calculate the time ?

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I dont think the propagation really depends on the input or output. Its a property of the gate's them selves. You need to find the sum of the gates propagation delays through the longest path in your circuit

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  • \$\begingroup\$ are you sure ? lets say : AND : Tp(LH)=10 ns , Tp(HL)=12 ns OR : Tp(LH)=12 NS , Tp(HL)=14 ns XOR: Tp(LH)=14 , Tp(HL)= 16 ns. Then what's Tp(LH) for : a0 -> q2 = ?? \$\endgroup\$ – Mahmoud Qahawish Dec 23 '15 at 5:58
  • \$\begingroup\$ High and low prop delays could be different as one depends on a n channel device and the other depends on a p. Most manufacturers will try to match the delays closely. \$\endgroup\$ – Krunal Desai Dec 23 '15 at 7:19

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