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
； 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)
The highest frequency occurs when the data is 1010101010…….
. From the Fourier series This sequence produces a square wave with periodic time ；;2；E
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.