Draw a 3 bit full adder using three 1 bit full adders to add...

Draw a 3-bit full adder using three 1-bit full adders to add two 3-bit numbers A and B. See Module 2.1 (Lecture 3B) slide 12 for an example of a 1-bit full adder. Hint: Your circuit will have the following inputs and outputs: Three A inputs labeled A1, A2, A3 Three B inputs labeled B1, B2, B3 Initial Carry-In input labeled Carry-In1 Final Carry-out output labeled Carry-out3 Three SUM outputs labeled Sum1, Sum2, Sum3. Note: There will be 2 Carry-In inputs and 2 Carry-Out outputs inside the circuit that are used to connect the full adders but that are not considered as outputs for the circuit.

Transcript

00:01 Hello students, in this question we are going to draw the circuit of 3 -bit full adder using 3 input 3 1 -bit full adders to add 3 -bit numbers a and b.

00:18 So, here the input a has 3 bits.

00:24 This is a1, a2 and a3.

00:31 Example 0 0 0, this is the lsb and this is msb.

00:37 So, it has 3 bits and the input b has 3 bits that is b1, b2, b3.

00:49 So, this is 0 0 0 example.

00:56 Now, if we want to add these 2 numbers that is a1, a has 3 bits that is a1, a2, a3 and b has 3 bits.

01:05 This is b1, b2 and b3.

01:09 Now, we want to add this 2 number.

01:11 Initially there will be no carry.

01:13 So, this is let it be carry in 1 and if we add this 2 numbers we get a sum and a carry.

01:21 So, here the sum is represented by s1 and the carry is represented by c1 and now for the second bit we will add this 3 numbers that is c1, a2 and b2.

01:33 Here we get a sum s2 and a carry c2.

01:39 Now, for the third bit we will add these 3 numbers that is c2, a3 and b3.

01:44 Here we get a sum s3 and we get a carry c3 or we can write it as c out.

01:52 So, this is the operation we are going to perform.

01:56 So, let's draw the circuit.

01:59 For designing this circuit we have to use 3 1 bit full adders.

02:04 Fa means full adders.

02:05 So, full adder has 3 inputs and 1 carry, 1 sum output.

02:11 So, here for the first 1 bit full adder the inputs will be a1, b1 and c in 1.

02:22 So, this is what i have explained here.

02:24 So, this is a1, b1 and a carry c in 1 is fed out as input.

02:32 Now, here we get 2 outputs.