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The World Leader in High Performance Signal Processing Solutions
FUNDAMENTALS OF DESIGN
Class 1
Introduction
Presented by David Kress
The Goal
Capture what is going on in the real world
Convert into a useful electronic format
Analyze, Manipulate, Store, and Send
Return to the real world
The real world is NOT digital
Analog to Electronic signal processing
Sensor
(INPUT)Digital ProcessorAmp Converter
Actuator
(OUTPUT)Amp Converter
The Sensor
Sensor
(INPUT)Digital ProcessorAmp Converter
Actuator
(OUTPUT)Amp Converter
Analog, but
NOT
electronic
Analog
AND
electronic
Popular sensors
Sensor Type Output
Thermocouple Voltage
Photodiode Current
Strain Gauge Resistance
Microphone Capacitance
Touch Button Charge Output
Antenna Inductance
Thermocouple
Very low level (µV/ºC)
Non-linear
Difficult to handle
Wires need insulation
Susceptible to noise
Fragile
Sensor Signal Conditioning
Sensor Amp
Analog,
electronic,
but “dirty”
Analog,
electronic,
and “clean”
•Amplify the signal to a noise-resistant level
•Lower the source impedance
•Linearize (sometimes but not always)
•Filter
•Protect
Types of Temperature Sensors
THERMOCOUPLE RTD THERMISTOR SEMICONDUCTOR
Widest Range:
–184ºC to +2300ºC
Range:
–200ºC to +850ºC
Range:
0ºC to +100ºC
Range:
–55ºC to +150ºC
High Accuracy and
Repeatability
Fair Linearity Poor Linearity Linearity: 1ºC
Accuracy: 1ºC
Needs Cold Junction
Compensation
Requires
Excitation
Requires
Excitation
Requires Excitation
Low-Voltage Output Low Cost High Sensitivity 10mV/K, 20mV/K,
or 1µA/K Typical
Output
Common Thermocouples
JUNCTION MATERIALS
TYPICAL
USEFUL
RANGE (ºC)
NOMINAL
SENSITIVITY
(µV/ºC)
ANSI
DESIGNATION
Platinum (6%)/ Rhodium-
Platinum (30%)/Rhodium
38 to 1800 7.7 B
Tungsten (5%)/Rhenium -
Tungsten (26%)/Rhenium
0 to 2300 16 C
Chromel - Constantan 0 to 982 76 E
Iron - Constantan 0 to 760 55 J
Chromel - Alumel –184 to 1260 39 K
Platinum (13%)/Rhodium-
Platinum
0 to 1593 11.7 R
Platinum (10%)/Rhodium-
Platinum
0 to 1538 10.4 S
Copper-Constantan –184 to 400 45 T
Thermocouple Output Voltages
for Type J, K and S Thermocouples
-250 0 250 500 750 1000 1250 1500 1750
-10
0
10
20
30
40
50
60T
HE
RM
OC
OU
PL
E O
UT
PU
T V
OL
TA
GE
(m
V)
TEMPERATURE (°C)
TYPE J
TYPE K
TYPE S
-250 0 250 500 750 1000 1250 1500 1750
-10
0
10
20
30
40
50
60T
HE
RM
OC
OU
PL
E O
UT
PU
T V
OL
TA
GE
(m
V)
TEMPERATURE (°C)
TYPE J
TYPE K
TYPE S
Thermocouple Seebeck Coefficient vs.
Temperature
-250 0 250 500 750 1000 1250 1500 1750
0
10
20
30
40
50
60
70S
EE
BE
CK
CO
EF
FIC
IEN
T -
µV
/ °C
TEMPERATURE (°C)
TYPE J
TYPE K
TYPE S
-250 0 250 500 750 1000 1250 1500 1750
0
10
20
30
40
50
60
70S
EE
BE
CK
CO
EF
FIC
IEN
T -
µV
/ °C
TEMPERATURE (°C)
TYPE J
TYPE K
TYPE S
Thermocouple Basics
T1
Metal A
Metal B
Thermoelectric
EMF
RMetal A Metal A
R = Total Circuit Resistance
I = (V1 – V2) / R
V1 T1 V2T2
V1 – V2
Metal B
Metal A Metal A
V1
V1
T1
T1
T2
T2
V2
V2
V
Metal AMetal A
Copper Copper
Metal BMetal B
T3 T4
V = V1 – V2, If T3 = T4
A. THERMOELECTRIC VOLTAGE
B. THERMOCOUPLE
C. THERMOCOUPLE MEASUREMENT
D. THERMOCOUPLE MEASUREMENT
I
V1 T1
Metal A
Metal B
Thermoelectric
EMF
RMetal A Metal A
R = Total Circuit Resistance
I = (V1 – V2) / R
V1 T1 V2T2
V1 – V2
Metal B
Metal A Metal A
V1
V1
T1
T1
T2
T2
V2
V2
V
Metal AMetal A
Copper Copper
Metal BMetal B
T3 T4
V = V1 – V2, If T3 = T4
A. THERMOELECTRIC VOLTAGE
B. THERMOCOUPLE
C. THERMOCOUPLE MEASUREMENT
D. THERMOCOUPLE MEASUREMENT
I
V1
Using a Temperature Sensor for Cold-
Junction Compensations
TEMPERATURE
COMPENSATION
CIRCUIT
TEMP
SENSORT2V(T2)T1 V(T1)
V(OUT)
V(COMP)
SAME
TEMP
METAL A
METAL B
METAL A
COPPERCOPPER
ISOTHERMAL BLOCKV(COMP) = f(T2)
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)
TEMPERATURE
COMPENSATION
CIRCUIT
TEMP
SENSORT2V(T2)T1 V(T1)
V(OUT)
V(COMP)
SAME
TEMP
METAL A
METAL B
METAL A
COPPERCOPPER
ISOTHERMAL BLOCKV(COMP) = f(T2)
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)
AD594/AD595 Monolithic Thermocouple
Amplifier with Cold-Junction Compensation
ICE
POINT
COMP
+
OVERLOAD
DETECT
VOUT10mV/°C
+5V
BROKEN
THERMOCOUPLE
ALARM
4.7k
G
+
–TC––
+TC+
+ATHERMOCOUPLE
G
AD594/AD595
TYPE J: AD594
TYPE K: AD595
0.1µF
ICE
POINT
COMP
+
OVERLOAD
DETECT
VOUT10mV/°C
+5V
BROKEN
THERMOCOUPLE
ALARM
4.7k
G
+
–TC––
+TC+
+ATHERMOCOUPLE
G
AD594/AD595
TYPE J: AD594
TYPE K: AD595
0.1µF
Basic Relationships For Semiconductor
Temperature Sensors
IC IC
VBE VN
VBE VBE VNkT
qN ln( )
VBEkT
q
ICIS
ln VN
kT
q
ICN IS
ln
INDEPENDENT OF IC, IS
ONE TRANSISTORN TRANSISTORS
Classic Bandgap Temperature Sensor
"BROKAW CELL"R R
+I2 @ I1
Q2
NA
Q1
A
R2
R1
VN VBE(Q1)
VBANDGAP = 1.205V
+VIN
VPTAT = 2R1
R2
kTq
ln(N)
VBE VBE VNkT
qN ln( )
Analog Temperature Sensors
Product Accuracy
(Max)
Max Accuracy
Range
Operating
Temp
Range
Supply
Range
Max
Current
Interface Package
AD590± 0.5°C
± 1.0°C
25°C
-25°C to 105°C
-55°C to
150°C4 to 30V 298uA Current Out
TO-52,2-ld FP,
SOIC, Die
AD592± 0.5°C
± 1.0°C
25°C
-55°C to 150°C
-25°C to
105°C4 to 30V
298uACurrent Out TO-92
TMP35 ± 2.0°C0°C to 85°C
-25°C to 100°C
-55°C to
150°C2.7 to 5.5V 50uA Voltage Out
TO-92, SOT23,
SOIC
TMP36 ± 3.0°C-40°C to 125°C -55°C to
150°C2.7V to 5.5V
50uAVoltage Out
TO-92, SOT23,
SOIC
AD22100± 2.0°C -50°C to 150°C -50°C to
150°C4 to 6.5V 650uA Voltage Out TO-92, SOIC, Die
AD22103± 2.5°C 0°C to 100°C 0°C to 100°C
2.7 to 3.6V 600uA Voltage Out TO-92, SOIC
Digital Temperature Sensors
Comprehensive Portfolio of Accuracy Options
21
Product Accuracy (Max) Max Accuracy
Range
Interface Package
ADT7420/7320± 0.2°C
± 0.25°C
-10°C to 85°C
-20°C to 105°CI2C/SPI LFCSP
ADT7410/7310 ± 0.5°C -40°C to 105°C I2C/SPI SOIC
ADT75± 1°C (B grade)
± 2°C (A grade)
0°C to 85°C
-25°C to 100°CI2C MSOP, SOIC
ADT7301± 1°C 0°C to 70°C
SPI SOT23, MSOP
TMP05/6± 1°C 0°C to 70°C
PWM SC70, SOT23
AD7414/5± 1.5°C -40°C to 70°C
I2C SOT23,MSOP
ADT7302 ± 2°C 0°C to 70°C SPI SOT23,MSOP
TMP03/4± 4°C
-20°C to 100°C PWM TO-92,SOIC,TSSOP
Position and Motion Sensors
Linear Position: Linear Variable Differential Transformers
(LVDT)
Hall Effect Sensors
Proximity Detectors
Linear Output (Magnetic Field Strength)
Rotational Position:
Optical Rotational Encoders
Synchros and Resolvers
Inductosyns (Linear and Rotational Position)
Motor Control Applications
Acceleration and Tilt: Accelerometers
Gyroscopes
LVDT – Linear Variable Differential
Transformer
~AC
SOURCE
VOUT = VA – VB
+
_
VOUT
POSITION+_
VOUT
POSITION+_
VA
VB
1.75"
THREADED
CORE
SCHAEVITZ
E100
A
B
AD698 LVDT Signal Conditioner
(Simplified)
AMP ~
+
_
FILTER AMP
VB
VOUT
AD698
EXCITATION
4-WIRE LVDT
OSCILLATORA
B
VA
REFERENCE
A, B = ABSOLUTE VALUE + FILTER
Hall Effect Sensors
I I
T
B
VH
CONDUCTOR
OR
SEMICONDUCTOR
I = CURRENT
B = MAGNETIC FIELD
T = THICKNESS
VH = HALL VOLTAGE
AD22151 Linear Output Magnetic
Field Sensor
_
+
CHOPPER
AMP
VCC / 2
R1
R2
R3
OUTPUT
AMP
VCC = +5V
VCC / 2
TEMP
REF
+
_
VOUT = 1 + R3
R20.4mV Gauss NONLINEARITY = 0.1% FS
AD22151 VOUT
Accelerometer Applications
Tilt or Inclination
Car Alarms
Patient Monitors
Cell phones
Video games
Inertial Forces
Laptop Computer Disc Drive Protection
Airbag Crash Sensors
Car Navigation systems
Elevator Controls
Shock or Vibration
Machine Monitoring
Control of Shaker Tables
ADI Accelerometer Fullscale g-Range: ± 2g to ± 100g
ADI Accelerometer Frequency Range: DC to 10kHz
ADXL-family Micro-machined
Accelerometers
FIXED
OUTER
PLATES
CS1 CS1< CS2= CS2
DENOTES ANCHOR
BEAM
TETHER
CS1 CS2
CENTER
PLATE
AT REST APPLIED ACCELERATION
Using an Accelerometer to Measure Tilt
X
0°
+90°
1g
Acceleration
X
–90°
–1g
0°
+1g
+90°
Acceleration = 1g × sin
0g
–90°
X
0°
+90°
1g
Acceleration
X
–90°
–1g
0°
+1g
+90°
Acceleration = 1g × sin
0g
–90°
Gyro Axes of Rotational Sensitivity
Coriolis acceleration example.
Displacement due to the Coriolis Effect
Photograph of mechanical sensor.
High Impedance Sensors
Photodiodes
Piezoelectric Sensors
Accelerometers
Hydrophones
Humidity Monitors
pH Monitors
Chemical Sensors
Smoke Detectors
Charge Coupled Devices and
Contact Image Sensors for Imaging
Photodiode Equivalent Circuit
PHOTO
CURRENTIDEAL
DIODE
INCIDENT
LIGHT
RSH(T)
100k -
100G
CJ
NOTE: RSH HALVES EVERY 10 C TEMPERATURE RISE
Current-to-voltage Converter (Simplified)
ISC = 30pA
(0.001 fc)
+
_
R = 1000M
VOUT = 30mV
Sensitivity: 1mV / pA
Preamplifier DC Offset Errors
~
VOS
IB
IB
R1
R21000M
+
_
IB DOUBLES EVERY 10 C TEMPERATURE RISE
R1 = 1000M @ 25 C (DIODE SHUNT RESISTANCE)
R1 HALVES EVERY 10 C TEMPERATURE RISE
DC NOISE GAIN = 1 + R2
R1
OFFSET
RTO
R3
R3 CANCELLATION RESISTOR NOT EFFECTIVE
Sensor Resistances Used In Bridge
Circuits Span A Wide Dynamic Range
Strain Gages 120, 350, 3500
Weigh-Scale Load Cells 350 - 3500
Pressure Sensors 350 - 3500
Relative Humidity 100k - 10M
Resistance Temperature Devices (RTDs) 100 , 1000
Thermistors 100 - 10M
Wheatstone Bridge Produces An Output Null
When The Ratios Of Sidearm Resistances Match
THE WHEATSTONE BRIDGE:
VO
R4
R1
R3
R2
VB
+
+
R3R2
R2
R4R1
R1VV BO
AT BALANCE,
VO R3
R2
R4
R1if0=
Output Voltage Sensitivity And Linearity Of Constant Current Drive
Bridge Configurations Differs According To The Number Of Active
Elements
R R
R R+R
R+R
R+R R+R R+R
RR R+R RRR R
R RR
VOVO VO
VO
IB IB IB IB
VO:
Linearity
Error:0.25%/% 0 0 0
IBR
4
R
R
4R +
IB2
R IB RIB2
R
(A) Single-Element
Varying
(B) Two-Element
Varying (1)(C) Two-Element
Varying (2)
(D) All-Element
Varying
R
R R
R
+
IN AMP
REF VOUT
RG
+VS
-VS*R+R
* SEE TEXT REGARDING
SINGLE-SUPPLY OPERATION
OPTIONAL RATIOMETRIC OUTPUTVB
VREF
= VB
VB4
R
R
2R +
VOUT = GAIN
A Generally Preferred Method Of Bridge Amplification Employs
An Instrumentation Amplifier For Stable Gain And High CMR
Upcoming webcasts
Converter Simulation: Beyond the Eval Board January 19th at 3:00 p.m. (ET)
RF Detectors February 16th at Noon (ET)
Challenges in Embedded Design for real-time systems
March 16th at Noon (ET)
www.analog.com/webcast
Fundamentals Webcasts 2011
January Introduction and Fundamentals of Sensors
February The Op Amp
March Beyond the Op Amp
April Converters, Part 1, Understanding Sampled Data Systems
May Converters, Part 2, Digital-to-Analog Converters
June Converters, Part 3, Analog-to-Digital Converters
July Powering your circuit
August RF: Making your circuit mobile
September Fundamentals of DSP/Embedded System design
October Challenges in Industrial Design
November Tips and Tricks for laying out your PC board
December Final Exam, Ask Analog Devices
www.analog.com/webcast