“Noise Characterization of A/D Converter on PIC Microcontroller”

EE 472 – Senior Project “Noise Characterization of A/D Converter on PIC Microcontroller” • Hang B. Lee, Applied Physics & EE • Advisor: Prof. Robert Grober

EE 472 – Senior Project 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

Project Goal EE 472 – Senior Project • Understand noise characteristics of A/D Converter • Investigate methods to minimize or eliminate noise • Artificially enhance resolution – software methods

A/D Converter 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

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 • Quantization noise (error due to discretizing) • Thermal noise • Reference voltage variations • Etc. What is the sum of all these contributions?

EE 472 – Senior Project Oversampling and Averaging • Artificially enhance resolution • Cost efficient alternative to paying for higher resolution BUT …. • Tradeoff throughput (High resolution means slower conversion speed) • More CPU intensive

EE 472 – Senior Project Requirements • 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

EE 472 – Senior Project 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 – Senior Project Labview Waveform

EE 472 – Senior Project Waveform Close-up

EE 472 – Senior Project Another Waveform

EE 472 – Senior Project Histogram – 88

EE 472 – Senior Project Histogram - 11

EE 472 – Senior Project Histogram – 255

EE 472 – Senior Project DC Histogram – 18

What Now? EE 472 – Senior Project • We understand that “effective” resolution is not nearly as good as maximum resolution • Dithering may help – introduce white noise then oversample and average

“Noise Characterization of A/D Converter on PIC Microcontroller”