Implementation of Logic Gates

a

b

1

f(a,b)

a b a + b

0 0 0

0 1 1

1 0 1

1 1 1

• OR gate

• Two problems

  • 1) when a=b=0, f(a,b) is undefined (floating)
  • 2) n- type switches do not conduct 1 well

• Two solutions

  • when f=0, connect output to 0v using n-type switches
  • when f=1, connect output to 5v using p-type switches

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