Transcript Analog to Digital Converter

Analog-Digital Converters
In presenting Order:
Josh Navikonis
Moiz H
Mike Hochman
Brian Post
ME 6405
9/29/2009
Agenda
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Introduction to ADC
Types of ADC
Characteristics of ADC in MC9S12C
Application and Selection of ADC
Introduction of ADC
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What is ADC?
Why is ADC important?
How does it work?
What is ADC?
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
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?
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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
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Achieved through sampling and holding circuit
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Switch ON – sampling of signal (time to charge capacitor w/ Vin)
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Switch OFF - voltage stored in capacitor (hold operation)

Must hold sampled value constant for digital conversion
Simple Sample and Hold Circuit
Response of Sample and Hold Circuit
Sampling
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Sampling rate depends on clock
frequency
Use Nyquist Criterion
Increasing sampling rate increases
accuracy of conversion
Possibility of aliasing
Sampling Signal: Tw
1
T
s 
Sampling Period:
fs
Nyquist Criterion: fs  2  f
max
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
fs  2  f
max
Quantizing and Encoding
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

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
Vrange=Input Voltage Range
n= # bits of ADC
resolution  Vrange /( 2n  1)
Example:
Vrange  7.0V
n3
1V  7V /( 23  1)
Resolution
Qerror  resolution / 2
 .5V
Resolution
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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
Types of A/D Converters
Presenter : Moiz H
Flash A/D Converter
Successive Approximation A/D Converter
Example of Successive Approximation
Dual Slope A/D Converter
Delta – Sigma A/D Converter
Elements of a Flash A/D Converter
Encoder
Comparator
FLASH A/D CONVERTER
Resolution
23-1 = 7 Comparators
3 Bit Digital Output
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
Cons
• Each additional bit
of resolution
requires twice the
number of
comparators
•Expensive
• Prone to produce
glitches in the
output
Elements of Dual-Slope ADC
Integrator
Dual-Slope ADC
*
Elements of the Successive Approximation ADC
Successive Approximation Register
Digital to Analog Converter
Takes in a Combination of Bits
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.
Vin = 6.84 V
Vref = 10
V
5
7.5
7.5
6.25
6.25
6.875
6.5625
6.5625
6.71875
6.796875
6.796875
6.8359375
6.8359375
6.84 V
DAC Input
DAC Vout
Cumulative
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
Dual Slope A/D Converter Contd.
Pros
• High accuracy
• Fewer adverse
affects from noise
Cons
• Slow
• Accuracy is
dependent on the
use of precision
external
components
Delta-Sigma ADC
Delta-Sigma ADC contd.
#1 Delta-Sigma Modulator
Delta-Sigma ADC contd.
#2 Digital Filter
Decimator
Sigma-Delta A/D Converter Contd.
Pros
•High Resolution
•No need of
precision
components
Cons
• Slow due to over
sampling
• Good for low
bandwidth
ADC Comparison
Type
Speed(relative)
Cost(Relative)
Dual Slope
Slow
Med
Flash
Very fast
High
Successive approx
Medium fast
Low
Sigma-Delta
Slow
Low
ATD10B8C on MC9S12C32
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Presented by:
 Michael
Hochman
MC9S12C32 Block Diagram
ATD10B8C Block Diagram
ATD10B8C Key Features
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Resolution
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Conversion Time
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8/10 bit (manually chosen)
7 usec, 10 bit
Successive Approximation ADC architecture
8-channel multiplexed inputs
External trigger control
Conversion modes
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Single or continuous sampling
Single or multiple channels
ATD10B8C External Pins
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12 external pins

AN7 / ETRIG / PAD7
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AN6/PAD6 – AN0/PAD0
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Analog input
General purpose digital I/O
VRH, VRL
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Analog input channel 7
External trigger for ADC
General purpose digital I/O
High and low reference voltages for ADC
VDDA, VSSA

Power supplies for analog circuitry
ATD10B8C Registers
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6 Control Registers ($0080 - $0085)
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2 Status Registers ($0086, $008B)
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Formatted results (2 bytes)
1 Digital Input Enable Register ($008D)
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Allows for analog conversion of internal states
16 Conversion Result Registers ($0090 - $009F)
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General status information regarding ADC
2 Test Registers ($0088 - $0089)
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Configure general ADC operation
Convert channels to digital inputs
1 Digital Port Data Register ($008F)
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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
What is Data Acquisition
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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
NI X-Series Data Acquisition Card
Control Systems
e*(∆t)
t
R
+
-
e
S/H
&
ADC
t
∆t
e*(∆t)
u*(∆t)
Digital
CPU
Controller
Clock
Digital Control System
Transducer
1001
0010
1010
0101
e*
0010
0101
0011
1011
e
u*(∆t)
Controller
∆t
D/A
&
Hold
Y
u
Plant
The Old Way…. Analog Computers
Comdyna GP6
The New Way
e*(∆t)
t
t
Controller
1001
0010
1010
0101
e*
0010
0101
0011
1011
e
u*(∆t)
∆t
∆t
Analog
Output
Analog
Input
ADC
D/A
Programmable Logic Controllers
ADC in PLCs
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PLCs are the industry standard for
automation tasks including:
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designed for:
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Motion Control
Safety Systems
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
Rockwell PLC
Analog I/O Module
Sensor Integration (Robotics)
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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
Why Digital?
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Digital signals can be easily
manipulated
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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-toanalog conversion chips translate the
outgoing audio signal from analog
to digital and the incoming signal
from digital back to analog
Audio Devices
Examples
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ADCs are integral to current
music reproduction technology
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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
ADC From Sound Card
Video Devices
TV Tuners
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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
Selection of an ADC
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Important Considerations:
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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
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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
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Select a satisfactory Analog to Digital Converter….
Example Continued
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Desired Signal:

Sensitivity: (±2.0%) 100 mV/g

Measurement Range: ±50 g pk

Frequency Range: (±5%) 0.5 to 10000 Hz
Solution
Vrange
resolution  n
2 1
Freq: f s min  2 * f max
Resolution:
Minimum Sampling
Ideal Sampling Freq:
f s min  5 * f max
n
ln(
10
 1)
0.1
 6.66 bit  8 bit
ln( 2)
f s min  5 *10000 Hz
 50000 Hz
Choosing AD7892
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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 onchip 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
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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