Post Lab 7 Answer Sheet


Be sure to include all your lab partners names with this submission.

Sampling Questions

1) At what frequency did you notice the aliasing frequency was nearly zero? How does it compare to the sampling frequency?




2) At what frequency did you notice the reproduced freq was half the sampling frequency? Does this follow the aliasing prediction? (Hint: Consider the sampling frequency)




3) At what frequency did you begin to notice quantizing steps in the reproduced signal? In light of the sample frequency, why does this become easy to observe?




4) For the on 1KHz source frequency example, how many quantizing steps did you observer per cycle? What is the ratio of the source frequency to the sampling frequency? How does this compare to the number of quantizing steps you observe?



5) The amplitude of the low pass signal was considerably lower than expected for the 3db down frequency. This is from the DAC source resistance output loading the filter and effectively changing the 3b down point frequency. After adjusting the source frequency, at what freq did you find the 3db point to be?




6) Given the RC values of the filter and the measured 3db freq, what value do you think the DAC source resistance is? Hint: The combined filter resistance is the DAC source resistance plus the filter resistance. Check the SmartFusion specification and see how the DAC source resistance compares to your calculated value. Smartfusion Data Sheet Hint: Search for DAC output impedance.









Quantization Questions

Submit the results of your quantization measurements.
Voltage Range (mv) Conversion Value
                              0  <---> 0
                                  <---> 0<-->1 unstable
                                  <---> 1
                                  <---> 1<-->2 unstable
                                  <---> 2
                                  <---> 2<-->3 unstable
                                  <---> 3
                                  <---> 3<-->4 unstable

1) What is the voltage range for the first conversion interval (0)? How might this voltage range have come about (hint: think binary...)



2) What is the voltage range for the subsequent intervals? How might this voltage range have come about (hint: think binary...)



3) What transfer function graph illustrated in the In-Lab does this ADC represent?



4) Is there any advantage generally speaking to this transfer function compared to the other? (Hint: Consider how the quantizing error is expressed.)




Accelerometer Questions


1a) What is the voltage of the Y axis when the proto-board is oriented flat on the desk?


1b) When you tilt the board to the right, what smallest voltage you read on the Y axis?


1c) When you tilt the board to the left , what largest voltage you read on the Y axis ?


1d)  How many volts per G do you observe?


1e)  Is this consistent with the specification?





2) Show your calculations for determining Raccel. Do these compare with the accelerometer specification.  Freescale MMA7361L