In presenting Order: Josh Navikonis Moiz H Mike Hochman Brian Post Analog-Digital Converters ME /29/2009

Agenda  Introduction to ADC  Types of ADC  Characteristics of ADC in MC9S12C  Application and Selection of ADC

Introduction of ADC  What is ADC?  Why is ADC important?  How does it work?

What is ADC?  ADC (Analog to Digital Converter) is an electronic device that converts a continuous analog input signal to discrete digital numbers (binary)  Analog  Real world signals that contain noise  Continuous in time  Digital  Discrete in time and value  Binary digits that contain values 0 or 1

Why is ADC Important?  All microcontrollers store information using digital logic  Compress information to digital form for efficient storage  Medium for storing digital data is more robust  Digital data transfer is more efficient  Digital data is easily reproducible  Provides a link between real-world signals and data storage

How ADC Works 2 Stages:  Sampling  Sample-Hold Circuit  Aliasing  Quantizing and Encoding  Resolution Binary output

Sampling  Reduction of a continuous signal to a discrete signal  Achieved through sampling and holding circuit  Switch ON – sampling of signal (time to charge capacitor w/ V in )  Switch OFF - voltage stored in capacitor (hold operation)  Must hold sampled value constant for digital conversion Response of Sample and Hold Circuit Simple Sample and Hold Circuit

Sampling  Sampling rate depends on clock frequency  Use Nyquist Criterion  Increasing sampling rate increases accuracy of conversion  Possibility of aliasing Sampling Signal: Sampling Period: Nyquist Criterion:

Aliasing  High and low frequency samples are indistinguishable  Results in improper conversion of the input signal  Usually exists when Nyquist Criterion is violated  Can exist even when:  Prevented through the use of Low-Pass (Anti-aliasing) Filters

Quantizing and Encoding  Approximates a continuous range of values and replaces it with a binary number  Error is introduced between input voltage and output binary representation  Error depends on the resolution of the ADC

Resolution  Maximum value of quantization error  Error is reduced with more available memory Example: V range =Input Voltage Range n= # bits of ADC Resolution

 Increase in resolution improves the accuracy of the conversion Minimum voltage step recognized by ADC Analog Signal Digitized Signal- High Resolution Digitized Signal- Low Resolution

Flash A/D Converter Successive Approximation A/D Converter Example of Successive Approximation Dual Slope A/D Converter Delta – Sigma A/D Converter Types of A/D Converters Presenter : Moiz H

Elements of a Flash A/D Converter Encoder Comparator

FLASH A/D CONVERTER 3 Bit Digital Output Resolution = 7 Comparators

Flash A/D Converter Contd. Pros Fastest (in the order of nano seconds) Simple operational theory Speed is limited only by gate and comparator propagation delay Each additional bit of resolution requires twice the number of comparators Expensive Prone to produce glitches in the output Cons

Integrator Elements of Dual-Slope ADC

Dual-Slope ADC *

Elements of the Successive Approximation ADC Takes in a Combination of Bits Successive Approximation Register Digital to Analog Converter

SUCESSIVE APPROXIMATION A/D CONVERTER

Example Show the timing waveforms that would occur in SAR ADC when converting an analog voltage of 6.84V to 8-bit binary, assume that the full scale input voltage of the DAC is 10V. Vref = 10 V Vin = 6.84 V

DAC InputDAC Vout Cumulative Voltage D D D D D D D D V

Dual Slope A/D Converter Contd. Pros High accuracy Fewer adverse affects from noise Slow Accuracy is dependent on the use of precision external components Cons

Delta-Sigma ADC

#1 Delta-Sigma Modulator Delta-Sigma ADC contd.

#2 Digital Filter Delta-Sigma ADC contd. Decimator

Sigma-Delta A/D Converter Contd. Pros High Resolution No need of precision components Slow due to over sampling Good for low bandwidth Cons

TypeSpeed(relative)Cost(Relative) Dual SlopeSlowMed FlashVery fastHigh Successive approxMedium fastLow Sigma-DeltaSlowLow ADC Comparison

ATD10B8C on MC9S12C32  Presented by:  Michael Hochman

MC9S12C32 Block Diagram

ATD10B8C Block Diagram

ATD10B8C Key Features  Resolution  8/10 bit (manually chosen)  Conversion Time  7 usec, 10 bit  Successive Approximation ADC architecture  8-channel multiplexed inputs  External trigger control  Conversion modes  Single or continuous sampling  Single or multiple channels

ATD10B8C External Pins  12 external pins  AN7 / ETRIG / PAD7 Analog input channel 7 External trigger for ADC General purpose digital I/O  AN6/PAD6 – AN0/PAD0 Analog input General purpose digital I/O  V RH, V RL High and low reference voltages for ADC  V DDA, V SSA Power supplies for analog circuitry

ATD10B8C Registers  6 Control Registers ($ $0085)  Configure general ADC operation  2 Status Registers ($0086, $008B)  General status information regarding ADC  2 Test Registers ($ $0089)  Allows for analog conversion of internal states  16 Conversion Result Registers ($ $009F)  Formatted results (2 bytes)  1 Digital Input Enable Register ($008D)  Convert channels to digital inputs  1 Digital Port Data Register ($008F)  Contains logic levels of digital input pins

Control Register 2

Control Register 3

Control Register 4

Control Register 5

Single Channel Conversions

Multi-channel Conversions

Status Register 0

Status Register 1

Results Registers

ATD Input Enable Register

Port Data Register

Setting up the ADC

Applications For ADC  What are some applications for Analog to Digital Converters?  Measurements / Data Acquisition  Control Systems  PLCs (Programmable Logic Controllers)  Sensor integration (Robotics)  Cell Phones  Video Devices  Audio Devices

Measurements / Data Acquisition  The sampling of the real world to generate data that can be manipulated by a computer  (DSP) Digital Signal Processing first requires a digital signal  Eg. Analysis of data from weather balloons by the National Weather Service What is Data AcquisitionNI X-Series Data Acquisition Card

Control Systems S/H & ADC Digital CPU Controller D/A & Hold Plant Transducer Clock Digital Control System + - R Y tt ee* Controller ∆t e*(∆t) ∆t u*(∆t) e e*(∆t) u*(∆t) u

The Old Way…. Analog Computers Comdyna GP6

The New Way tt ee* Controller ∆t e*(∆t) ∆t u*(∆t) ADC Analog Input D/A Analog Output

Programmable Logic Controllers  PLCs are the industry standard for automation tasks including:  Motion Control  Safety Systems  designed for:  multiple inputs and output arrangements  extended temperature ranges  immunity to electrical noise  resistance to vibration and impact  Most I/O are Boolean, however most PLC systems have an analog I/O module ADC in PLCsRockwell PLC Analog I/O Module

Sensor Integration (Robotics)  Many robots use microprocessors  ADC allows robots to interpret environmental cues and compensate  If the algorithm needs to be changed it’s a simple matter of modifying the code  Analog control systems require a complete circuit redesign

Cell Phones  Digital signals can be easily manipulated  Digital phones convert your voice into binary information and then compress it  This compression allows between three and 10 digital calls to occupy the space of a single analog call.  The analog-to-digital and digital-to- analog conversion chips translate the outgoing audio signal from analog to digital and the incoming signal from digital back to analog Why Digital?

Audio Devices  ADCs are integral to current music reproduction technology  They sample audio streams and store the digital data on media like compact disks  The current crop of AD converters utilized in music can sample at rates up to 192 kilohertz  Sound Cards ExamplesADC From Sound Card

Video Devices  Analog video and audio signals are converted to digital signals for display to user  Slingbox converts analog input stream and rebroadcasts it across the internet in digital form  CCDs use ADCs to process image data TV Tuners

Selection of an ADC  Important Considerations:  Input Type – Differential or Single Ended  Resolution - Most Important  Scaling - allows the user to divide or multiply the input voltage to more closely match the full scale range of the ADC  Sample Rate - The sample rate must be at least twice the frequency the you are measuring, but 5 times is much better  Channel Scan Rate - The channel scan rate is the maximum rate that the ADC can select a new channel and make a measurement. many ADCs have a relatively slow scan rate (when compared to the sample rate.) Eg. To achieve a sample rate of 600Hz on three channels, you will need a channel scan rate of at least 1.8kHz

Example: Selecting an ADC  We want to digitize a vibration signal measured by an accelerometer with the following characteristics (PCB 301A10):  Sensitivity: (±2.0%) 100 mV/g  Measurement Range: ±50 g pk  Frequency Range: (±5%) 0.5 to Hz  Select a satisfactory Analog to Digital Converter….

Example Continued  Desired Signal:  Sensitivity: (±2.0%) 100 mV/g  Measurement Range: ±50 g pk  Frequency Range: (±5%) 0.5 to Hz  Resolution:  Minimum Sampling Freq:  Ideal Sampling Freq: Solution

Choosing AD7892  From Analog Devices:  The AD7892 is a high speed, low power, 12-bit A/D converter that operates from a single +5 V supply. The part contains a 1.47 µs successive approximation ADC, an on-chip track/hold amplifier, an internal +2.5 V reference and on- chip versatile interface structures that allow both serial and parallel connection to a microprocessor. The part accepts an analog input range of ±10 V or ±5 V. Overvoltage protection on the analog inputs for the AD and AD allows the input voltage to go to ±17 V or ±7 V respectively without damaging the ports.

References  Cetinkunt, Sabri. Mechatronics 2007   en.wikipedia.org/    Bishop, Ron. Basic Microprocessors and the 6800  MC912SC Family Data Sheet  MC912SC Reference Manual  MC912SC Programming Reference Guide