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BASEBAND DIGITAL DATAdoc

By Albert Smith,2014-07-04 21:32
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BASEBAND DIGITAL DATAdoc

BASEBAND DIGITAL DATA

    Common form of base band signals to represent digital information bits are shown below. Voltage levels for uni-polar and bi-polar signals are also shown.

BIT-RATE, BAUD-RATE & BANDWIDTH

    1

denotes the duration of the 1 bit B

    1 Hence Bit rate = bits per second B

    All the forms of the base band signalling shown transfer data at the same bit rate.

     denotes the duration of the shortest signalling element. E

    Baud rate is defined as the reciprocal of the duration of the shortest signalling element.

    1 i.e. Baud Rate = baud E

    In general Baud Rate ? Bit Rate

    For NRZ : Baud Rate = Bit Rate ( = ) BE

    B RZ : Baud Rate = 2 x Bit Rate ( = ) E2

    B Bi-Phase: Baud Rate = 2 x Bit Rate ( = ) E2

     AMI: Baud Rate = Bit Rate

    A major consideration for base band signals is the minimum bandwidth and the upper and

    lower frequencies and respectively, in the signal. ffLH

    Considering bi-polar signal (i.e. V or +V)

    NRZ

The highest frequency occurs when the data is 1010101010…….

    i.e.

    2

    . From the Fourier series This sequence produces a square wave with periodic time ;2E

    strdthfor a square wave, this waveform contains 1, 3, 5 … (Odd) harmonics.

    If we pass this signal through a LPF then the maximum bandwidth would be 1/T Hz, i.e. to

    stjust allow the fundamental (1 harmonic) to pass. As illustrated in the diagram below, the data sequence 1010…… could then be completely covered.