PIC Microcontroller

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2 Νοε 2013 (πριν από 4 χρόνια και 10 μέρες)

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EE 472


Senior Project







Hang B. Lee, Applied Physics & EE



Advisor: Prof. Robert Grober








“Noise Characterization of A/D






Converter on PIC Microcontroller”

PIC Microcontroller


PIC: Programmable Interface Controller


Modifiable by end user:


-

Software
(C code)

-
Hardware
(modification to circuitry)


Common use in robotics and control applications


Potential use in data acquisition or measurement



EE 472


Senior Project

Project Goal


Understand noise characteristics of A/D Converter


Investigate methods to minimize or eliminate noise


Artificially enhance resolution


software methods


EE 472


Senior Project




10
-
bit resolution




8 channels for analog input





Throughput:
35,000 samples per sec





Method of conversion:



(i) sample and hold



(ii) successive approximation



A/D Converter

EE 472


Senior Project

Resolution


What is maximum resolution?






For 5V, maximum resolution ~ 5 mV


1 LSB represents 5mV increment


EE 472


Senior Project

A/D Converter Noise

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Quantization noise (error due to discretizing)


Thermal noise


Reference voltage variations


Etc.



What is the sum of all these contributions?





Oversampling and Averaging

EE 472


Senior Project


Artificially enhance resolution


Cost efficient alternative to paying for higher resolution



BUT ….



Tradeoff throughput


(High resolution means slower conversion speed)


More CPU intensive

Requirements

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Must be able to approximate sum of all noise
contributions as
white noise



White noise
has uniform power spectral density



Two ways to check for this:




(1) Histogram analysis



(2) Take FT of autocorrelation




Data Measurement


Built
-
in potentiometer / DC power supply


Labview collects digital output values


Histogram analysis




EE 472


Senior Project

Serial Interface


Serial interface PIC chip with PC


Receive streaming data from output pin


Approaches taken:

(1) Visual Basic


failed effort

(2) Labview


better




EE 472


Senior Project

Problems with Visual Basic


Buffer check requires too much time


Causes lag in data acquisition


Too slow for collecting large number of data points


EE 472


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Labview Waveform

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Waveform Close
-
up

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Another Waveform

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Histogram


88

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Histogram
-

11

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Histogram


255

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DC Histogram


18

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We understand that “effective” resolution is not

nearly as good as maximum resolution



Dithering may help


introduce white noise

then oversample and average


What Now?

EE 472


Senior Project