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Pulse Code Modulation
AM Radio Simulator
Group 6 Marck Christo Christopher pher M. Abias Abias Eugine Eug ine Cri Cristy sty A. Llama Llamass Suzette V. Sabido
Objectives: To briefly discuss the history of Pulse Amplitude Modulation To know the definition and types of PAM. To know how to generate a PAM signal To know how to demodulate PAM To discuss the applications and some problems of PAM.
Scope: Quick review of previous reported pulse modulation Brief History Definition Types of PAM Generation is PAM signal Demodulation of PAM signal Applications and problems with PAM.
History earliest reason for sampling a signal was to interlace samples from different telegraphy sources, and convey them over a single telegraph cable 1853 ² Telegraph time-d time-division ivision multiplexing (TDM) was conveyed by Moses G. Farmer
1903 1903 ² W. M. Miner used an electr electroomechanica mech anicall commu commuta tato torr for TDM of multiple telegraph signals, and also applied this technology to telephony. He obtained intelligible speech from channels sampled at a rate above 3500²4300 Hz: below this was unsatisfactory.
PAM simplest form of pulse modulation modulation in which the amplitude of a series of regularly spaced pulses is varied in accordance with the modulating signal can also be used for generating additional pulse modulations
There
are two types of PAM: Natural PAM Flat top PAM
Natur al al PAM sampling occurs
when finite width pulses are used in the modulation and tops of pulses follow the modulating signal
Flat tops
top PAM
of the pulses are flat the pulses have a constant amplitude within the pulse interval
Note
: Sometimes, PAM is also classified as«
PAM
signal gener ation
PAM signal is generated by using a pulse train, called the sampling signal (or clock signal) to operate an electronic switch or ´chopper´ This produces samples of the analog message signal
PAM signal generation
atural al Natur
sampling ² genera sampling generation tion of PAM signals. signals.
Natural
sampling ² time domain appearance of a PAM signal
PAM signal generation
lat-top p Flat-to
sampling ² gener sampling generation ation of PAM signals. signals.
lat-top p Flat-to
sampling ² time domain appearance appearance of a PAM signal.
PAM Demodulator
Disadvantages The BW required for transmission of a PAM signal is very large Noise is maximum in the PAM wave. As the amplitude of the PAM signal is varied, this also varies peak power required by the transmitter
Applications Ethernet o
e.g. Fast Ethe Ethernet rnet 100BA 100BASESE-T2 medium (now defunct)
Photobiology o
PAM fluorom fluoromete eterr ² used for the stud study y of phot photosyn osynthe thesis sis
Electronic drivers for LED lighting o
for lighting applications
Conclusion PAM is rather stringent in its system requirement, such as short duration of pulse. Also, the noise performance of PAM may not be sufficient for long distance transmission. Accordingly, PAM is often used as a mean of message processing for time-division multiplexing, from which conversion to some other form of pulse pul se modulation is subsequently made.
