I need help with the following questions 1. If a particular 4-bit adder contains

Question

I need help with the following questions

1. If a particular 4-bit adder contains 20 gates, then how many gates would be required for an 8-bit adder if it utilized these 4 bit adders in a carry select adder configuration?

2. Recalculate question (1), but this time consider that the 4-bit adders are configured as ripple adders

3. If each of these 4 bit adders takes 10 nsec and there is a 1 nsec delay between adders, how long will it take two get the result from the 8-bit adder described in question 2?

4. Recalculate question (4), but this time consider that the 4-bit adders are configured as ripple adders

PLease help

thanks

Explanation / Answer

2)Carry select adder contains two ripple carry adders...hence for every 2 bits, it has 2 (2bit)adders..

now, in this situation..

The number of gates required for 8-bit adder (utilizing 4 bit adders) in carry select configuration:

For normal 8bit-adder, we need 2, 4bit adders

but in carry select adder configuration, for 8bit-adder, we need 4, 4bit adders,

hence the number of gates required are 4*20 = 80 gates

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