Input and Output with the DSK - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 72

4. In the echo program example, add a repetitive echo effect so that if a repeti-
tive echo effect is desired, buffer [i]

output (or input for no repetitive effect).
5. Implement an AM scheme to obtain an AM signal using an external input as
the sideband signal and a 2-kHz carrier signal from a lookup table. Test your
results using a sampling frequency of 8 kHz, and a sinusoidal input signal with
amplitude below 0.35 V and frequency less than 2 kHz (a higher input signal
frequency will cause aliasing). Such a small input signal as the sideband yields
a more stable output.
6. Write a program to generate a cosine signal of frequency 666 Hz when dip
switch #0 (SW0) is pressed (turning on LED #0), 1.33 kHz when SW1 is
pressed, 2 kHz when SW2 is pressed, and 2.66 kHz when SW3 is pressed. The
program could take the following shape: Start with a 12-point table repre-
senting the cosine values, sampling at 8 kHz. Build and test this program as
sine_4freq .
(a) Test if SW0 is pressed. If so, turn on LED #0. Then, while SW0 is still
pressed, the cosine is generated and a loop index is preincrementing to
step through every point in the table until the end of the table is reached.
This should generate the 666 Hz.
(b) Test if SW1 is pressed. If so, preincrement the loop index until the end of
the table is reached. Now, every other point is selected so that the gener-
ated frequency is f

=

1.33 kHz.
(c) Repeat the previous step for SW2 so that four points are selected and
f

= F s /6 =

2 kHz, and repeat the previous step for SW3 so that three points
are selected and f

= F s /4 =

2.66 kHz. Note that to generate the 2.66 kHz,
all four switches need to be pressed.

= F s /3 =

REFERENCES

1. TLV320AIC23 Stereo Audio Codec, 8- to 96-kHz, with Integrated Headphone Amplifier

Data Manual , SLWS106G, Texas Instruments, Dallas, TX, 2003.

2. S. Norsworthy, R. Schreier, and G. Temes, Delta-Sigma Data Converters: Theory, Design

and Simulation , IEEE Press, Piscataway, NJ, 1997.

3. P. M. Aziz, H. V. Sorensen, and J. Van Der Spiegel, An overview of sigma delta convert-

ers, IEEE Signal Processing , Jan. 1996.

4. J. C. Candy and G. C. Temes, eds., Oversampling Delta-Sigma Data Converters: Theory,

Design and Simulation , IEEE Press, Piscataway, NJ, 1992.

5. C. W. Solomon, Switched-capacitor filters, IEEE Spectrum , June 1988.

6. PCM3002/PCM3003 16-/20-Bit Single-Ended Analog Input/Output Stereo Audio Codecs ,

SBAS079, Texas Instruments, Dallas, TX, 2000.

7. TMS320C6000 McBSP: AC'97 Codec Interface , SPRA528, Texas Instruments, Dallas, TX,

1999.