ELEC 3004/7312: Signals Systems & Controls · 2013-05-20 · ELEC 3004/7312: Signals Systems &...

The University of Queensland - School of Information Technology and Electrical Engineering of 22

ELEC 3004/7312: Signals Systems & Controls Prac/Lab 1: Introduction to the NEXYS 2 + Sampling & Reconstruction on the NEXYS 2 Revised March 17, 2013

Pre-Lab Note: The tutors will not assist you further unless there is real evidence you have attempted questions prior to the tutorial.

This laboratory is the combination of what used to be two sessions. This is now laboratory session with two experiments (i.e., Introduction to the NEXYS 2 and Sampling & Reconstruction on the NEXYS 2). The Pre-laboratory exercise for this laboratory is to : Read through Experiments I and II of the Laboratory 1 Guide

Read through the Experiment I Preparation

Read and Complete Experiment II Preparation (page 14)

Laboratory Completion & Extra Credit Points

Доверяй, но проверяй (doveryai, no proveryai – “Trust, but verify”)

Laboratory Completion: Please work together on the lab in groups of 2-3. Please submit an individual hand-in sheet. Treat the questions at the end of the Experiments as thought questions – questions that you should be able to answer, but not that you have to answer explicitly. Though you could be asked these during a tutor group review. Tutor Group Review: At various stages in the lab (or at the end) the tutors will come around to check progress. The may ask some questions to check your understanding. Each person in the group may get asked different questions at the tutor’s discretion. Based on your answers they will mark (initial) your hand-in sheet. The tutors are just checking that you understand the core ideas of each Experiment and its Parts. Extra Credit Points: This practical laboratory is worth 1-4 Extra Credit Points on the final exam. These will be distributed based on completion (as determined by the head tutor for your practical session) of the following sections at the end of the practical session.

Section Completed Total Points Extra

Credit Earned Pre-Lab (Preparation for Lab 1 – Experiment II – p. 14) + 1 Complete Experiment I + 2 Complete Experiment II – Part 1 & 2 + 3 Complete Experiment II – Part 3 + 4

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LAB 1 Experiment I: An Introduction to the NEXYS 2


Thought Questions

If you have the DAC Filter board available, the Raw signal is connected to the upper PMOD-CON4 connector and the Filtered signal is connected to the lower PMOD-CON4 connector.

Plot the output waveform/s on the oscilloscope. What is the amplitude and frequency of the sine wave generated on each available channel?

The Master Clock is 50MHz, which is then divided by 200, in clockdiv1.vhd, to produce Fr.

This frequency, Fr, controls the readout rate of the LUT which is n=16 elements long. If it takes 16 clock cycles of Fr to produce a complete LUT cycle, what is the theoretical audio output frequency? Is it the same as your measured frequency?

Try to confirm that the DAC step size is approximately the same as that calculated in the preparation. If it is not, can you explain why? Hint 1: is the DAC connected directly to the output? Hint 2: can you see a relationship between the steps in the output waveform, and the changes in the values in the LUT?

Suggest how you might modify the VHDL code so that a LUT with only 8 points is required. What are the

advantages and disadvantages of this approach?

LAB 1 Experiment I: An Introduction to the NEXYS 2


Appendix – Part 1: Sinewave.vhd library IEEE; use IEEE.std_logic_1164.all; use IEEE.std_logic_unsigned.all; entity SINEWAVE is port ( DATAOUT : out std_logic_vector(11 downto 0); SAMPLECLK : in std_logic ); end SINEWAVE; architecture behavioral of SINEWAVE is signal I : integer range 0 to 15; begin with I select DATAOUT <= "100000000000" when 0, --800 "101100001111" when 1, --B0F "110110100111" when 2, "111101100011" when 3, "111111111111" when 4, "111101100011" when 5, "110110100111" when 6, "101100001111" when 7, "100000000000" when 8, "010011110000" when 9, "001001011000" when 10, "000010011100" when 11, "000000000000" when 12, "000010011100" when 13, "001001011000" when 14, "010011110000" when 15; I <= I + 1 when rising_edge(SAMPLECLK);

end behavioral;

END PART I

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LAB 1 Experiment II: Sampling & Reconstruction on the NEXYS 2


If you look at the schematics in the appendix, you will see that there are connections for Raw Out and Filtered Out. This allows you to experiment with various combinations of input and output signals, being: 1. Raw in, Raw out 2. Raw in, Filtered out 3. Filtered in, Raw out 4. Filtered in, Filtered out. Slide switch 0, SW0, allows you to select raw In (0), or Filtered In (1) for the ADC. The DAC filter board has Raw Out on the top connector and Filtered Out on the bottom connector. Combination a) is the same as not having the filter boards at all. Part 3 continued: If you move SW0, you can select between a) and c) for the top connector (Raw Out), and between b) and d) for the bottom connector (Filtered Out).

Remember to keep the input pk-pk value under 5V. Connect the function generator to CH1 of the oscilloscope and the ADC. Set the function generator to Sinewave, 5 V p-p and DC offset of 2.5 volts.

For the following data, plot this in a spreadsheet and show to a tutor. 1. Connect the Raw Out (top connector) to CH2.

Raw in – Raw out

Move SW0 to 0 (Raw in) then sweep the frequency from about 100Hz to about 25 kHz and observe the output on CH2. Record the input and output amplitudes, plus Frequency Out at 1, 4, 10, 15 and 20 kHz.

Filtered in – Raw out

Now move SW0 to 1 (Filtered In) and repeat. Now connect Filtered out (bottom connector) to CH2.

Raw in – Filtered out Move SW0 to 0 (Raw in) then sweep the frequency from about 100Hz to about 25 kHz and observe the output on CH2. Record the input and output amplitudes, plus Frequency Out at 1, 4, 10, 15 and 20 kHz.

Filtered in – Filtered out

Now move SW0 to 1 (Filtered In) and repeat. Set the function generator to squarewave and repeat 1 to 6. Record the results in the tables below or in a spreadsheet. Either printout your plots, or save the files to your network drive for later review.



Data Entry Table

Sinewave Filtered in – Raw out (SW0 = 1)

Frequency in (kHz) Vin pk-pk Vout pk-pk Frequency out

1 4

10 15 20

Sinewave Raw in – Filtered out (SW0 = 0)


1 4 10 15 20

Sinewave Filtered in – Filtered out (SW0 = 1)


1 4 10 15

20

Squarewave Raw in – Raw out (SW0 = 0)


1

4

10

15

20

Squarewave Filtered in – Raw out (SW0 = 1)


1

4

10

15

20

Squarewave Raw in – Filtered out (SW0 = 0)


1

4

10

15

20

Squarewave Filtered in – Filtered out (SW0 = 1)


1

4

10

15

20

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This page is intentionally blank and be used as scratch paper



Experiment 1: Hand-In Sheet Introduction to the NEXYS 2 + Sampling & Reconstruction on the NEXYS 2

Name: Student ID: Date: Group Name/Members:

As noted, this practical laboratory is worth 1-4 Extra Credit Points on the final exam. These will be distributed based on completion (as determined by the head tutor for your practical session) of the following sections at the end of the practical session.

Section Completed Summary Comments (Student)

✓(Tutor)

Pre-Lab (Preparation Lab 1 – Section II) Complete Experiment I Complete Experiment II – Part 1 & 2 Complete Experiment II – Part 3

Continued on Page 22



Please succinctly answer the following questions for the various lab sections. Section I Q1) Suggest how you might modify the VHDL code so that a LUT with only 8 points is required. What are the advantages and disadvantages of this approach? List two of each. What is one overall benefit and downside to using a LUT? Section II Q2) Use this space to write your answers to the following questions from Part II:

a) Should the phase response be linear? Why or why not?

b) Explain, in terms of the Nyquist rate and sampling theory, what happens to the frequency of the output

wave when the input wave frequency is swept from 10 to 15 kHz.

Section III Q3) Summarise the differences between the four combinations of input and output signals experimented with in Part III. Note any differences between the sine wave and square wave outputs with the different combinations and provide a brief explanation.

Total Extra Credit Awarded: ________________________________________________________

Tutor Sign-Off: _______________________________________________________________________

ELEC 3004/7312: Signals Systems & Controls · 2013-05-20 · ELEC 3004/7312: Signals Systems &...

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Transcript of ELEC 3004/7312: Signals Systems & Controls · 2013-05-20 · ELEC 3004/7312: Signals Systems &...