Class 1 - Introduction and designing with sensors, such as: Thermocouple Photodiode Strain Gauge Microphone Touch Button Antenna

1. The World Leader in High Performance Signal Processing Solutions
FUNDAMENTALS OF DESIGN
Class 1
Introduction
Presented by David Kress

2. 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

3. The real world is NOT digital

4. Analog to Electronic signal processing
Sensor Amp Converter Digital Processor
(INPUT)
Actuator Amp Converter
(OUTPUT)

5. The Sensor
Analog, but Analog
Sensor
NOT (INPUT) AND
Amp Converter Digital Processor
electronic electronic
Actuator Amp Converter
(OUTPUT)

6. Popular sensors
Sensor Type Output
Thermocouple Voltage
Photodiode Current
Strain Gauge Resistance
Microphone Capacitance
Touch Button Charge Output
Antenna Inductance

7. Thermocouple
 Very low level (µV/ºC)
 Non-linear
 Difficult to handle
 Wires need insulation
 Susceptible to noise
 Fragile

8. Sensor Signal Conditioning
Sensor Amp
Analog, Analog,
electronic, electronic,
but “dirty” and “clean”
•Amplify the signal to a noise-resistant level
•Lower the source impedance
•Linearize (sometimes but not always)
•Filter
•Protect

9. Types of Temperature Sensors
THERMOCOUPLE RTD THERMISTOR SEMICONDUCTOR
Widest Range: Range: Range: Range:
–184ºC to +2300ºC –200ºC to +850ºC 0ºC to +100ºC –55ºC to +150ºC
High Accuracy and Fair Linearity Poor Linearity Linearity: 1ºC
Repeatability Accuracy: 1ºC
Needs Cold Junction Requires Requires Requires Excitation
Compensation Excitation Excitation
Low-Voltage Output Low Cost High Sensitivity 10mV/K, 20mV/K,
or 1µA/K Typical
Output

10. Common Thermocouples
TYPICAL NOMINAL ANSI
JUNCTION MATERIALS USEFUL SENSITIVITY DESIGNATION
RANGE (ºC) (µV/ºC)
Platinum (6%)/ Rhodium- 38 to 1800 7.7 B
Platinum (30%)/Rhodium
Tungsten (5%)/Rhenium - 0 to 2300 16 C
Tungsten (26%)/Rhenium
Chromel - Constantan 0 to 982 76 E
Iron - Constantan 0 to 760 55 J
Chromel - Alumel –184 to 1260 39 K
Platinum (13%)/Rhodium- 0 to 1593 11.7 R
Platinum
Platinum (10%)/Rhodium- 0 to 1538 10.4 S
Platinum
Copper-Constantan –184 to 400 45 T

11. Thermocouple Output Voltages
for Type J, K and S Thermocouples
THERMOCOUPLE OUTPUT VOLTAGE (mV) 60
50
TYPE K
40 TYPE J
30
20
TYPE S
10
0
-10
-250 0 250 500 750 1000 1250 1500 1750
TEMPERATURE (°C)

12. Thermocouple Seebeck Coefficient vs.
Temperature
70
60 TYPE J
SEEBECK COEFFICIENT - µV/ °C
50
TYPE K
40
30
20
TYPE S
10
0
-250 0 250 500 750 1000 1250 1500 1750
TEMPERATURE (°C)

13. Thermocouple Basics
A. THERMOELECTRIC VOLTAGE C. THERMOCOUPLE MEASUREMENT
Metal A Metal A
V1 – V2
Metal A
V1 T1 Thermoelectric V1 T1 T2 V2
EMF
Metal B Metal B
B. THERMOCOUPLE D. THERMOCOUPLE MEASUREMENT
Copper Copper
Metal A R Metal A V
Metal A Metal A
I T3 T4
V1 T1 T2 V2 V1 T1 T2 V2
Metal B Metal B
R = Total Circuit Resistance
I = (V1 – V2) / R V = V1 – V2, If T3 = T4

14. Using a Temperature Sensor for Cold-
Junction Compensations
V(OUT) TEMPERATURE
V(COMP) COMPENSATION
CIRCUIT
COPPER COPPER
METAL A SAME METAL A
TEMP TEMP
SENSOR
T1 V(T1) V(T2) T2
METAL B
V(COMP) = f(T2)
ISOTHERMAL BLOCK
V(OUT) = V(T1) – V(T2) + V(COMP)
IF V(COMP) = V(T2) – V(0°C), THEN
V(OUT) = V(T1) – V(0°C)

15. AD594/AD595 Monolithic Thermocouple
Amplifier with Cold-Junction Compensation
+5V
0.1µF BROKEN
4.7k THERMOCOUPLE VOUT
ALARM 10mV/°C
OVERLOAD
TYPE J: AD594 DETECT
TYPE K: AD595
THERMOCOUPLE AD594/AD595 +A
– – –TC
ICE
G + G POINT
+ + COMP
+TC

16. Basic Relationships For Semiconductor
Temperature Sensors
IC IC
N TRANSISTORS
ONE TRANSISTOR
VBE VN
kT  IC  kT  IC 
VBE  ln  VN  ln 
q  IS  q  N  IS 
kT
VBE  VBE  VN  ln(N)
q
INDEPENDENT OF IC, IS

17. Classic Bandgap Temperature Sensor
+VIN
R R "BROKAW CELL"
+ VBANDGAP = 1.205V
I2 @ I1
Q2 Q1
NA A
VN VBE
kT
VBE  VBE  VN  ln(N) R2 (Q1)
q
R1 kT
VPTAT = 2 ln(N)
R2 q
R1

18. Analog Temperature Sensors
Product Accuracy Max Accuracy Operating Supply Max Interface Package
(Max) Range Temp Range Current
Range
± 0.5°C 25°C -55°C to TO-52,2-ld FP,
AD590 4 to 30V 298uA Current Out
± 1.0°C -25°C to 105°C 150°C SOIC, Die
± 0.5°C 25°C -25°C to 298uA
AD592 4 to 30V Current Out TO-92
± 1.0°C -55°C to 150°C 105°C
0°C to 85°C -55°C to TO-92, SOT23,
TMP35 ± 2.0°C 2.7 to 5.5V 50uA Voltage Out
-25°C to 100°C 150°C SOIC
TO-92, SOT23,
-40°C to 125°C -55°C to 50uA
TMP36 ± 3.0°C 2.7V to 5.5V Voltage Out SOIC
150°C
± 2.0°C -50°C to 150°C -50°C to
AD22100 4 to 6.5V 650uA Voltage Out TO-92, SOIC, Die
150°C
± 2.5°C 0°C to 100°C 0°C to 100°C
AD22103 2.7 to 3.6V 600uA Voltage Out TO-92, SOIC

19. Digital Temperature Sensors
Comprehensive Portfolio of Accuracy Options
Product Accuracy (Max) Max Accuracy Interface Package
Range
± 0.2°C -10°C to 85°C
ADT7420/7320 I2C/SPI LFCSP
± 0.25°C -20°C to 105°C
ADT7410/7310 ± 0.5°C -40°C to 105°C I2C/SPI SOIC
± 1°C (B grade) 0°C to 85°C
ADT75 I2C MSOP, SOIC
± 2°C (A grade) -25°C to 100°C
± 1°C 0°C to 70°C
ADT7301 SPI SOT23, MSOP
± 1°C 0°C to 70°C
TMP05/6 PWM SC70, SOT23
± 1.5°C -40°C to 70°C
AD7414/5 I2C SOT23,MSOP
ADT7302 ± 2°C 0°C to 70°C SPI SOT23,MSOP
± 4°C
TMP03/4 -20°C to 100°C PWM TO-92,SOIC,TSSOP
21

20. 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

21. +
THREADED
CORE VA
~ VOUT = VA – VB
AC
SOURCE VB
1.75"
_
VOUT VOUT
SCHAEVITZ
_ POSITION + _ POSITION +
E100
LVDT – Linear Variable Differential
Transformer

22. AD698
EXCITATION AMP ~ REFERENCE
OSCILLATOR
B
VB
+
A VOUT
FILTER AMP
B
A
VA
A, B = ABSOLUTE VALUE + FILTER
_
4-WIRE LVDT
AD698 LVDT Signal Conditioner

23. Hall Effect Sensors
T CONDUCTOR
OR
SEMICONDUCTOR
I I
VH
I = CURRENT
B
B = MAGNETIC FIELD
T = THICKNESS
VH = HALL VOLTAGE

24. AD22151 Linear Output Magnetic
Field Sensor V / 2 V = +5V CC
CC VCC / 2
R2
+
R1 TEMP
REF _ R3
_
AD22151 VOUT
+
OUTPUT
AMP
CHOPPER
AMP
VOUT = 1 + R3 0.4mV Gauss NONLINEARITY = 0.1% FS
R2

25. 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

26. ADXL-family Micro-machined
Accelerometers
AT REST CS1 CS2 APPLIED ACCELERATION
CENTER
PLATE
TETHER
BEAM
CS1 CS1
= CS2 < CS2
FIXED
OUTER
PLATES
DENOTES ANCHOR

27. Using an Accelerometer to Measure Tilt
+90° X
X 1g
 Acceleration
0°
–90°
+1g
Acceleration = 1g × sin 
0g 
–90° 0° +90°
–1g

28. Gyro Axes of Rotational Sensitivity

29. Coriolis acceleration example.

30. Displacement due to the Coriolis Effect

31. Photograph of mechanical sensor.

32. 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

33. Photodiode Equivalent Circuit
INCIDENT
LIGHT
PHOTO RSH(T)
CURRENT CJ
IDEAL
DIODE 100k -
100G
NOTE: RSH HALVES EVERY 10 C TEMPERATURE RISE

34. Current-to-voltage Converter (Simplified)
R = 1000M
ISC = 30pA
(0.001 fc)
_
VOUT = 30mV
+ Sensitivity: 1mV / pA

35. Preamplifier DC Offset Errors
1000M R2
IB
~ _
OFFSET
VOS RTO
R1
IB
+
R3 DC NOISE GAIN = 1 + R2
R1
IB DOUBLES EVERY 10 C TEMPERATURE RISE
R1 = 1000M @ 25 C (DIODE SHUNT RESISTANCE)
R1 HALVES EVERY 10 C TEMPERATURE RISE
R3 CANCELLATION RESISTOR NOT EFFECTIVE

36. 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

37. Wheatstone Bridge Produces An Output Null
When The Ratios Of Sidearm Resistances Match
VB
THE WHEATSTONE BRIDGE:
R4 R3
 R1 R2 
VO  VB   
 R1 + R4 R2 + R3 
VO AT BALANCE,
R1 R2
VO = 0 if 
R4 R3
R1 R2

38. Output Voltage Sensitivity And Linearity Of Constant Current Drive
Bridge Configurations Differs According To The Number Of Active
Elements
IB IB IB IB
R R R+R R R RR R+R RR
VO VO VO VO
R R+R R R+R R R+R RR R+R
R
VO: IBR R
IB
R
IB
R IB R
4 R + 2 2
4
Linearity
0.25%/% 0 0 0
Error:
(A) Single-Element (B) Two-Element (C) Two-Element (D) All-Element
Varying Varying (1) Varying (2) Varying

39. A Generally Preferred Method Of Bridge Amplification Employs
An Instrumentation Amplifier For Stable Gain And High CMR
VB
OPTIONAL RATIOMETRIC OUTPUT
VREF = VB
+VS
R R
R
 VB
VOUT = R GAIN
4 R +
RG 2
IN AMP
REF VOUT
+
R
R+R -VS*
* SEE TEXT REGARDING
SINGLE-SUPPLY OPERATION

40. Upcoming webcasts
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 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
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 October Challenges in Industrial Design
 November Tips and Tricks for laying out your PC board
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