1. ECE 3130 Digital Electronics and Design
Lab 5: Subtractors
Fall 2017
Priyankar Roychowdhury

2. Lab#5 Objectives Build and simulate a full subtractor.
Two XORs
Two Inverters
Two ANDs = NAND + Inverter
One OR = NOR + Inverter
Build and simulate a 4-bit subtractor.

3. Full Subtractor Truth Table A B B_in D B_out 1 Half Subtractor
Implementation A B
B_in D
B_out 1
Half Subtractor

4. Full Subtractor - schematic

5. Full Subtractor – symbol

6. Full Subtractor – test circuit

7. Full Subtractor – waveforms

8. 4-bit Subtractor - schematic

9. 4-bit Subtractor – simulation
Test your 4-bit subtractor by setting up inputs:
A=0101, B=1101, Borrow_in=1
Simulate it and check the results, which should be:
D=0111, Borrow_out=1
P.S. A=0101 means A0=1, A1=0, A2=1, A3=0

10. 4-bit Subtractor – test circuit

11. 4-bit Subtractor – waveforms