Analog to digital converters, adc

In this presentation i tried to describe the concept and application of ADC.

1. By: Saumya Ranjan Behura
Analog-Digital Converters

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

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

4. 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

5. 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

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

7. 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

8. Sampling
Sampling rate depends on clock
frequency
Use Nyquist Criterion
Increasing sampling rate
increases accuracy of conversion
Possibility of aliasing
max2ffs*>
s
s
f
T
1
=
Sampling Signal:
Sampling Period:
Nyquist Criterion:
wT

9. 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
max2ffs*>

10. 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

11. Resolution
)12/(-=
n
rangeVresolution
)12/(71
3
0.7
3
-=
=
=
VV
n
VVrange
Maximum value of quantization error
Error is reduced with more available memory
Example:
V
range
=Input Voltage Range
n= # bits of ADC
Resolution
V
resolutionQerror
5.
2/
±=
±=

12. 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

13. 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

14. Elements of a Flash A/D Converter
Encoder
Comparator

15. FLASH A/D CONVERTER
3 Bit Digital Output
Resolution

2
3
-1 = 7 Comparators

16. 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

17. Integrator
Elements of Dual-Slope ADC

18. Dual-Slope ADC
*

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

20. SUCESSIVE APPROXIMATION A/D CONVERTER

21. 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

22. 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
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

23. 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

24. Delta-Sigma ADC

25. #1 Delta-Sigma Modulator
Delta-Sigma ADC contd.

26. #2 Digital Filter
Delta-Sigma ADC contd.
Decimator

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

28. Type Speed(relative) Cost(Relative)
Dual Slope Slow Med
Flash Very fast High
Successive approx Medium fast Low
Sigma-Delta Slow Low
ADC Comparison

29. ATD10B8C on MC9S12C32
Presented by:
Michael Hochman

30. MC9S12C32 Block Diagram

31. ATD10B8C Block Diagram

32. 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

33. 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

34. 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

35. Control Register 2

36. Control Register 3

37. Control Register 4

38. Control Register 5

39. Single Channel Conversions

40. Multi-channel Conversions

41. Status Register 0

42. Status Register 1

43. Results Registers

44. ATD Input Enable Register

45. Port Data Register

46. Setting up the ADC

47. 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

48. 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

49. Control Systems
S/H
&
ADC
Digital
CPU
Co ntro lle r
D/A
&
Hold
Plant
Transduce
r
Clock
Digital Control System
+
-
R
Y
t t
e e*
Controller
0
0
1
0
0
1
0
1
0
0
1
1
1
0
1
1
∆t
e*(∆t)
1
0
0
1
0
0
1
0
1
0
1
0
0
1
0
1
∆t
u*(∆t)
e
e*(∆t) u*(∆t)
u

50. The Old Way…. Analog
Computers
Comdyna  GP6

51. The New Way
t t
e e*
Controller
0
0
1
0
0
1
0
1
0
0
1
1
1
0
1
1
∆t
e*(∆t)
1
0
0
1
0
0
1
0
1
0
1
0
0
1
0
1
∆t
u*(∆t)
ADC
Analog
Input
D/A
Analog
Output

52. 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

53. 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

54. 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?

55. 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

56. 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

57. 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

58. 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….

59. 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
Vrange
resolution
maxmin
*2ff
s
=
maxmin
*5ff
s
=
Solution
bitbitn 866.6
)2ln(
)1
1.0
10
ln(
Þ=
+
=
Hz
Hzf
s
50000
10000*5
min
=
=

60. 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.

61. 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

62. THANK YOUTHANK YOU