Digital Electronics Quick Notes:

Digital Counters are of 2 Types:


(i) Synchronous Counters:

    - A Clock is attached to all the FF’s
    - The input to the FF is a function of output(s) of other FF’s
    - D Type FF is used in Synchronous Counters
    - Its faster than Asynchronous Counters
    - Synchronous counters are also called Shift Counters.


    Types of Shift Counters (Synchronous Counters):

    (i) Ring Counter :
        - The output Q of the last FF is connect to the input of first FF.
        - Mod 2 counter have 2 FF’s , can count 2 states.
        - Mod 3 counter have 3 FF’s , can count 3 states.

        Counting States:
        ———————
        For ’N’ FF’s ,  counting states are ’N’
        Ex:  A ring counter with 4 FF’s can counter 4 states.

       

    (ii) Johnson Counter ( or Twisted Ring Counter ) :
        - The output Q” of the last FF is connected to the input of the first FF.
        - Mod 4 counter have 2 FF’s , can count 4 states.
        - Mod 6 counter have 3 FF’s , can count 6 states.

   
        Counting States:
        ———————
        For ’N’ FF’s ,  counting states are ’2N’
        Ex:  A Johnson counter with 3 FF’s can counter 6 states.



(ii)Asynchronous Counters:

    - Asynchronous counters are also called Ripple Counters.
    - A Clock is attached to the first FF.
    - The output of each FF is given as clock signal to the next FF.
    - T Type FF is used in Asynchronous Counters
    - Its slower than Synchronous Counters due to the propagation delay in the FF’s
    - It can be used as Up Counter or Down Counter.
    - Mod 8 counter have 3 FF’s , can count 8 states.


    Counting States:
    ———————
    For ’N’ FF’s ,  counting states are power(2,N)
    Ex:  An Asynchronous counter with 3 FF’s can counter 8 states.