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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:32 |
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Conference: Bucharest University Faculty of Physics 2010 Meeting
Section: Biophysics and Medical Physics;Electricity and Magnetism
Title:
Discrete modulated digital transmitter
Authors:
Cristian Grecu(1), Alexandru Stanculescu(2)
Affiliation:
(1) Politehnica University of Bucharest, Faculty of Electronics, Telecommunications and Information Technology
(2) Politehnica University of Bucharest, Faculty of Applied Sciences
E-mail
grecucris@yahoo.com, i.slack@yahoo.com
Keywords:
discrete modulation, delta–sigma modulator, optoelectronic devices
Abstract:
Modulation is the process of varying the parameters of a signal, depending of an input signal, enabling it to be transmitted through a channel.
Apart from the traditional methods of modulation, there is also the discrete modulation, which modifies one of the parameters of an array of impulses. One way of doing this is using a delta-sigma modulator, which modifies the length of the impulses from an array according to the input signal.
The delta-signal modulator was invented in 1960, but it hasn`t been used until the `80s. Today it`s used in various electronic devices: digital modulators, analog-digital converters and commutation amplifiers.
We have designed and constructed a delta-sigma modulator, trying to obtain a linear modulation coefficient using general purpose integrated circuits, (operational amplifiers, inverters and a D-type latch ) and using only one power supply.
The heart of this modulator is represented by the double slope integrator. This is formed by an amplifier having the feedback through a capacitor, and provides at its output a slope proportional with the input signal. This works in two steps: Firstly, the output voltage is integrated, until it reaches a threshold. During the second step, a negative voltage is integrated, starting from the previous value, until the lower threshold is reached. The process repeats. On the rising slope, the output of the modulator is `1`, and else it is `0`. Thus the latch is determined to switch at a frequency of 100KHz, representing the sampling rate. So we determined that the modulator can easily handle audio frequency signals with a resolution of 6 bits.
Our practical experiment consists of a delta-sigma modulator and a demodulator. An audio source is connected to the modulator, which gives pulses to a IR LED, converting the pules into IR light. This is received by a photo transistor, transformed into electric signals, demodulated, amplified and rendered in a speaker.
References:
1. Wikipedia
2. The Art of Electronics, Paul Horowitz, Winfield Hill
3. United States Patent Number 4920544
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