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Filtering properties of AND and OR gates

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• Filter
  • Filter:

    Filter = a a device that can reduce or enhance certain aspects of a signal See: click here

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  • AND gates and OR gates can work as an all or nothing filter:

    We can use AND gates (or OR gates) to perform one of the following 2 operations: Allow an input signal to pass the AND gate (or OR gate) Block an input signal from passing the AND gate (or OR gate)

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• The AND-gate as a filter
  • Suppose we have a 4 bit binary number 1101.

    Consider the following circuit:

    When the signal c (for control) is equal to 1, the AND gates will let the input number 1101 pass.

    But if the control signal c is equal to 0, the AND gates will block the input number 1101:

    Notice that when the OR gates blocks, the output signals (= bits) are all equal to o.

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs355001/demo/circuits/and-filter

    How to run the program:

    To run: /home/cs355001/bin/cs355sim and-filter

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• The OR-gate as a filter
  • Suppose we have a 4 bit binary number 1101.

    Consider the following circuit:

    When the signal c (for control) is equal to 0, the OR gates will let the input number 1101 pass.

    But if the control signal c is equal to 1, the AND gates will block the input number 1101:

    Notice that when the OR gates blocks, the output signals (= bits) are all equal to 1.

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs355001/demo/circuits/or-filter

    How to run the program:

    To run: /home/cs355001/bin/cs355sim or-filter

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• Comment
  • Due to the fact that the output signals are all equal to 1 when blocking, the OR gate is not used to filter input signals

  • We will use AND gates to perform the filtering function

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• Using OR gates to collate multiple signals into 1 signal
  • Another use of the OR gate is to:

    collate multiple signals into one single signal where - under a specific condition - the output signal is equal to the active input signal

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  • Consider the following circuit with 5 input signals where 4 of the inputs are equal to 0:

    In the above figure, the first input is active (while the other 4 inputs are equals to 0).

    The output signal will be equal to the active signal (= input 0)

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  • Consider the same circuit with 5 input signals where the 3rd (= middle) input is active:

    In the above figure, the 3rd input is active (while the other 4 inputs are equals to 0).

    The output signal will be equal to the active signal (= input 2)

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs355001/demo/circuits/or-collate

    How to run the program:

    To run: /home/cs355001/bin/cs355sim or-collate