EPFEOO3LAB - DIGITAL COMMUNICATIONS Engr. GILBERT DETERA
LABORATORY INSTRUCTOR
Name: See, Joa Allen A. Date Performed: April 16, 2015Section:
GEN1 Lab Activity Title: DELTA-SIGMA MODULATIONLaboratory Activity
No. : 7
OBJECTIVES To observe the main characteristics of delta-sigma
modulation To understand principles of delta-sigma modulation
MATERIALS AND EQUIPMENT Ateneo de Naga UniversityCollege of
EngineeringElectronics and Computer Engineering DepartmentSummerS/Y
2014 2015 TIMS301 Digital Multimeter Connectors Digital
Oscilloscope Adder Delta Modulation Utilities
PROCEDURE
Note: Make sure that all instruments to be used are properly
connected and in good working conditions, e.g. all probes should be
checked for connectivity to avoid errors.
1. Before plugging in the delta modulator utilities module
decide upon the integrator time constant, then set it with switches
SW2A and SW2B2. Adjust both ADDER gains to unity, and both BUFFER
AMPLIFIER gains to unity. Throughout the experiment the gain g of
the ADDER (acting as the SUMMER) will not be changed.3. Patch
together the complete delta-sigma modulator according to Figure
4.4. Use a lowpass filter as a demodulator.
FIGURE
DATA OUTPUTDelta-sigma 2kHz message input
Using audio oscillator as message@ 580 Hz
@ 4 kHz
@ 8 kHz
ANALYSIS/OBSERVATION:We now examine a variation of delta
modulation which is the delta-sigma modulation. From the figures
given, I observe that the delta-sigma modulator places an
integrator between the message and the summer of the basic delta
modulator. From our data, we can see that the output is just like
the basic delta modulation, one noticeable feature is that a
delta-sigma is capable to shape the quantization noise. Using
different messages, the behaviour of the modulator is almost the
same as delta modulation. The only difference is that a low
frequencies, the integrator output is a pure sine wave. While at
higher frequencies, the integrator output looks almost the same as
the integrator output in delta modulation.
CONCLUSION:Sigma-delta modulation is perhaps best understood by
comparison with traditional pulse code modulation. From out
previous experiment, a PCM converter typically samples an input
signal at the Nyquist frequency and produces an N-bit
representation of the original signal. This technique, however,
requires quantization to 2N levels. There are times that high
resolution is difficult to obtain in PCM conversion due to the need
to accurately represent many quantization levels and the subsequent
circuit complexity. This is the motivation for sigmadelta
modulation, a form of pulse-density modulation, which exploits
oversampling and sophisticated filter design in order to employ a
low-bit quantizer with high effective resolution. Delta-sigma
modulation converts the analog voltage into a pulse frequency. The
substitution of frequency for voltage is entirely natural and
carries in its train the transmission advantage of a pulse
stream.
REFERENCE:http://en.wikipedia.org/wiki/Delta-sigma_modulation
