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