In presenting Order:

Josh Navikonis

Moiz H

Mike Hochman

Brian Post

Analog-Digital Converters

ME 6405

9/29/2009

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/

Vin) Switch OFF - voltage stored in capacitor (hold operation) Must hold sampled value constant for digital conversion

Response of Sample and Hold CircuitSimple Sample and Hold Circuit

Sampling

Sampling rate depends on clock frequency

Use Nyquist Criterion Increasing sampling rate

increases accuracy of conversion

Possibility of aliasing

max2 ffs

s

sf

T1

Sampling Signal:

Sampling Period:

Nyquist Criterion:

wT

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

max2 ffs

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

)12/( nrangeVresolution

)12/(71

3

0.7

3

VV

n

VVrange

Maximum value of quantization error Error is reduced with more available memory

Example:

Vrange=Input Voltage Range

n= # bits of ADC

Resolution

V

resolutionQerror

5.

2/

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 ConvertersPresenter : Moiz H

Elements of a Flash A/D Converter

Encoder

Comparator

FLASH A/D CONVERTER

3 Bit Digital Output

Resolution

23-1 = 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 Input DAC VoutCumulative Voltage

D7 5.0000 5.0000

D6 2.5000 7.5000

D5 1.2500 8.7500

D4 0.6250 9.3750

D3 0.3125 9.6875

D2 0.15625 9.84375

D1 0.078125 9.921875

D0 0.0390625 9.9609375

6.84 V

5

7.5

6.25

6.875

6.5625

6.71875

6.796875

6.8359375

5

7.5

6.25

6.875

6.5625

6.71875

6.796875

6.8359375

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

Type Speed(relative) Cost(Relative)

Dual Slope Slow Med

Flash Very fast High

Successive approx Medium fast Low

Sigma-Delta Slow Low

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

VRH, VRL High and low reference voltages for ADC

VDDA, VSSA Power supplies for analog circuitry

ATD10B8C Registers

6 Control Registers ($0080 - $0085) Configure general ADC operation

2 Status Registers ($0086, $008B) General status information regarding ADC

2 Test Registers ($0088 - $0089) Allows for analog conversion of internal states

16 Conversion Result Registers ($0090 - $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 Acquisition NI X-Series Data Acquisition Card

Control Systems

S/H&

ADC

Digital CPU

Controller

D/A &

HoldPlant

Transducer

Clock

Digital Control System

+

-

R Y

t t

e e*Controller0

01

0010

1001

1101

1

∆t

e*(∆t)

100

1001

0101

0010

1

∆t

u*(∆t)

e

e*(∆t) u*(∆t)

u

The Old Way…. Analog Computers

Comdyna  GP6

The New Way

t t

e e*Controller0

01

0010

1001

1101

1

∆t

e*(∆t)

100

1001

0101

0010

1

∆t

u*(∆t)

ADC

AnalogInput

D/A

AnalogOutput

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 PLCs Rockwell 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

Examples ADC 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 10000 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 10000 Hz

Resolution: Minimum Sampling Freq: Ideal Sampling Freq:

12

n

Vrangeresolution

maxmin *2 ff s

maxmin *5 ff s

Solution

bitbitn 866.6)2ln(

)11.0

10ln(

Hz

Hzf s50000

10000*5min

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 AD7892-1 and AD7892-3 allows the input voltage to go to ±17 V or ±7 V respectively without damaging the ports.

References

Cetinkunt, Sabri. Mechatronics 2007 www.me.gatech.edu/mechatronics_course en.wikipedia.org/ www.engineer.tamuk.edu/ www.scm.tees.ac.uk Bishop, Ron. Basic Microprocessors and the

6800 MC912SC Family Data Sheet MC912SC Reference Manual MC912SC Programming Reference Guide