This document summarizes a circuit design for precision tilt measurements using a dual-axis accelerometer. It discusses using single-axis and dual-axis accelerometers to measure tilt, with dual-axis providing accuracy over the full 360° range without ambiguity. The CN0189 circuit conditions the signals from an ADXL203 dual-axis accelerometer using an AD8608 op amp, then digitizes with an AD7887 ADC. It achieves 0.5° accuracy over 360° using algorithms that minimize output error. Evaluation hardware, software and design files are provided to demonstrate the solution.

1. Instrumentation: Test and
Measurement Methods and Solutions
Reference Designs and System Applications

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2

3. Today’s Agenda
Understand challenges of precision data acquisition in sensing
applications
 Complex impedance measurements over a wide range (CN0217)
 Tilt measurements over full 360° range using dual axis low-g iMEMS®
accelerometers (CN0189)
 Weigh scale signal conditioning and digitization of low level signals with high
noise-free code resolution (CN0216, CN0102)
Applications selected to illustrate important design principles
applicable to a variety of precision sensor conditioning circuits
including MEMS
See tested and verified Circuits from the Lab® signal chain solutions
chosen to illustrate design principles
 Low cost evaluation hardware and software available
 Complete documentation packages:
 Schematics, BOM, layout, Gerber files, assemblies
3

4. Circuits from the Lab
 Circuits from the Lab reference circuits are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges.
4
 Evaluation board hardware
Design files and software
 Windows evaluation software
 Schematic
 Bill of material
 PADs layout
 Gerber files
 Assembly drawing
 Product device drivers

5. System Demonstration Platform (SDP-B, SDP-S)
 The SDP (System Demonstration Platform) boards provide intelligent USB
communications between many Analog Devices evaluation boards and
Circuits from the Lab boards and PCs running the evaluation software
5
USB USB
EVALUATION
BOARD
SDP-B
SDP-S
EVALUATION
BOARD
POWER POWER
 SDP-S (USB to serial engine based)
 One 120-pin small footprint connector
 Supported peripherals:
 I2C
 SPI
 GPIO
 SDP-B (ADSP-BF527 Blackfin® based)
 Two 120-pin small footprint connectors
 Supported peripherals:
 I2C
 SPI
 SPORT
 Asynchronous parallel port
 PPI (parallel pixel interface)
 Timers

6. Impedance Measurement Applications
Consumer and biomedical markets
 High end biomedical equipment
 Resistivity/conductivity of biomedical tissues
 Medical sample analysis
 Consumer
 Medical sample analysis (e.g., glucose)
Industrial and instrumentation markets
 Electro impedance spectrometry
 Corrosion analysis
 Liquid condition analysis
 Sensor interface (sensor impedance changes with some external event)
6

7. Impedance Measurement Devices
Impedance measurement is a
difficult signal processing task
Need to measure complex
impedances, not just R, L, or C
Impedance conversion
 …is becoming more important in many
sensor/diagnostic related applications
 …is traditionally accomplished using
discrete solutions
 …usually requires a high level of
analog design skill to extract frequency
responses of the unknown impedance
7

8. Impedance Measurement Challenge
Problem:
 How to analyze a complex
impedance
 How to control ADC sampling
frequency with respect to DDS
output frequency (windowing
vs. coherent sampling)?
 How to manage component
selection?
 Must develop software to
control DDS
 Software required for FFT
 How to calculate error budget?
 What about temperature effects?
 Usually ends up consuming greater
board area and cost?
8
Excitation/Stimulus
Frequency Response
Analysis
Integrated
Single-Chip
SolutionAD5933
DDS Filter Buffer
ADC

9. VDD/2
DAC
Z(ω)
SCL
SDA
DVDDAVDDMCLK
AGND DGND
ROUT VOUT
AD5933
RFB
VIN
05324-001
1024-POINT DFT
I2C
INTERFACE
IMAGINARY
REGISTER
REAL
REGISTER
OSCILLATOR
DDS
CORE
(27 BITS)
TEMPERATURE
SENSOR
ADC
(12 BITS)
LPF
GAIN
AD5933/AD5934 Impedance Converter
 1 kΩ to 10 MΩ impedance range
 12-bit impedance resolution
 100 kHz maximum excitation frequency
 Adjustable voltage excitation
 User programmable frequency sweep
 Single frequency capability
 1 MSPS SAR ADC (AD5933)
 DFT carried out at each frequency point
 Manual calibration routine
 Single-chip solution with internal DSP
 Output at each frequency is real and imaginary
data word
 Simple off-chip processing required to calculate
magnitude and phase
9
I2C
INTERFACE
TO µC
OR PC
UNKNOWN
IMPEDANCE
EXCITATION
FREQUENCY
REAL AND IMAGINARY
COMPONENT
REGISTERS
DDS
ADJUSTABLE
VOLTAGE
EXITATION
CURRENT TO
VOLTAGE
CONVERTER

10. CN0217: High Accuracy Impedance
Measurements Using 12-Bit Impedance Converters
Circuit features
 Wide impedance range
 12-bit accuracy
 Analog front end (AFE) for
impedance measurements less
than 1 kΩ
Circuit benefits
 Self contained DDS excitation
 DSP for calculating DFT
 Complex impedance
measurements
10
Target Applications Key Parts Used Interface/Connectivity
Medical
Consumer
Industrial
AD5933
AD8606
I2C (AD5933)
USB (EVAL-AD5933EBZ)

11. 50kΩ
50kΩ
50kΩ
50kΩ
RFB
20kΩ
20kΩ
47nF
ZUNKNOWN
VDD
VDD
VDD
+
+
−
−
A1
A2
A1, A2 ARE
½ AD8606
1.48V
1.98V p-p
VDD/2
1.98V p-p
VDD/2
DAC
SCL
SDA
DVDDAVDDMCLK
AGND DGND
ROUT
VOUT
AD5933/AD5934
RFB
VIN
1024-POINT DFT
I2C
INTERFACE
IMAGINARY
REGISTER
REAL
REGISTER
OSCILLATOR
DDS
CORE
(27 BITS)
TEMPERATURE
SENSOR
TRANSMIT SIDE
OUTPUT AMPLIFIER
ADC
(12 BITS)
LPF
GAIN
VDD VDD
09915-001
I-V
CN0217 External AFE Signal Conditioning
 External analog front end (AFE) allows impedance
measurements below 1 kΩ
 The solution is based on the AD8605/AD8606 op amp
 Excitation stage: low Output Z (<1 Ω) up to 100 kHz
 Receive stage: low bias current (<1 pA)
11
VDD = 3.3V

12. High Accuracy Performance from the
AD5933/AD5934 with External AFE
12
30 35 40
FREQUENCY (kHz)
45 50
8160
8180
8200
8220
8240
8260
8280
IMPEDANCEMAGNITUDE(Ω)
R3
IDEAL
09915-008
35
30
25
20
15
10
5
0
29.95 30.00 30.05 30.10 30.15 30.20
10.3Ω
30Ω
1µF
30.25
FREQUENCY (kHz)
MAGNITUDE(Ω)
09915-003
Magnitude Results For ZC = 10 kΩ||10 nF, RCAL = 1 kΩ
Magnitude Results For Low Impedance ZC = 8.21 kΩ, RCAL = 99.85 kΩ
ZC = 217.25 kΩ, RCAL = 99.85 kΩ
One calibration
using 99.85 kΩ
resistor
covers
wide range
Allows low
value
impedance
measurements
Tracks R||C
across frequency
30 35 40
FREQUENCY (kHz)
45 50
IMPEDANCEMAGNITUDE(kΩ)
R4
09915-009
213.5
214.0
214.5
21.50
215.5
216.0
216.5
217.0
217.5
218.0
218.5
IDEAL
500
0
1000
1500
2000
2500
3000
3500
4000
4 24 44 64 84 104
IMPEDANCEMAGNITUDE(Ω)
FREQUENCY (kHz)
IDEAL
MEASURED
09915-011

13. Low RON SPDT CMOS Switch Used to Switch
Between RCAL and Unknown Z
13
Use low RON CMOS
switch for switching
from unknown impedance
to calibration resistor
RON = 0.5Ω

14. CN0217 Evaluation Board, EVAL-CN0217-EB1Z
14
 Complete design files
 Schematic
 Bill of material
 PADs layout
 Gerber files
 Assembly drawing
PC
Unknown Z
USB

15. AD5933 Web Based Demonstration Tool
Web tool demo:
 Enter different
impedance types
 Generate frequency
sweep
 Examine impedance
plot
15

16. AD5933 Used with AFE for Measuring Ground-
Referenced Impedance in Blood-Coagulation
Measurement System
16
Ground-referenced
Unknown Z

17. Blood Clotting Factor Measurements
17

18. Liquid Quality Impedance Measurement
18
CONDUCTANCE
LIQUID
MEASUREMENT
SWITCHES
AFE
AD5933/
AD5934
CONTROLLER
CALIBRATION
IMPEDANCE
UNKNOWN
IMPEDANCE

19. Precision Tilt Measurements
 Fundamentals of iMEMS (micro electro mechanical systems)
accelerometers
 Single axis tilt measurements
 Dual axis tilt measurements for better accuracy (CN0189)
 Signal conditioning
19

20. Why Use Accelerometers to Measure Tilt?
 Pendulums/potentiometers wear out
 Accuracy and bandwidth is limited
 Reliability is lower
 Takes up a large area
 Out of plane sensitivity/mechanical interference
 MEMS accelerometers are the latest proven technology
for electronically measuring tilt
 Good accuracy and bandwidth
 Small board area
 Low power
 High reliability
 Minimal out of plane sensitivity
20

21. Applications of iMEMS Accelerometers
Tilt or inclination
 Car alarms
 Patient monitors
Inertial forces
 Laptop computer disc drive protection
 Airbag crash sensors
 Car navigation systems
 Elevator controls
Shock or vibration
 Machine monitoring
 Control of shaker tables
 Data loggers to determine events/damage
ADI accelerometer full-scale g-range: ±2g to ±100g
ADI accelerometer frequency range: DC to 1 kHz
21

22. Tilt Measurements Using Low g Accelerometers
Need accuracy over full 360° arc
Output error less than 0.5°
Single-supply operation
Low power
CN0189 illustrates the signal chain solution
 Accelerometer signal conditioning
 Easy to use SAR ADC
 Low power, single supply
 Hardware, software, and design files available
22

23. ADXL-Family Micromachined iMEMS
Accelerometers (Top View of IC)
23
FIXED
OUTER
PLATES
CS1 CS1 < CS2= CS2
DENOTES ANCHOR
BEAM
TETHER
CS1 CS2
CENTER
PLATE
AT REST APPLIED ACCELERATION

24. ADXL-Family iMEMS Accelerometers
Internal Signal Conditioning
24
OSCILLATOR A1
SYNCHRONOUS
DEMODULATOR
BEAM
PLATE
PLATE
CS1
CS2
SYNC
0°
180°
A2
VOUT
CS2 > CS1
APPLIEDACCELERATION

25. Using a Single Axis Accelerometer to
Measure Tilt
25
X
0°
+90°
q
1g
Acceleration
X
–90°
–1g
0°
+1g
+90°
Acceleration = 1g × sin q
q0g
–90°
 Highest sensitivity between
−45 and +45
 Ambiguous beyond 90

26. Single Axis vs. Dual Axis Acceleration
Measurements
26
Output Acceleration vs. Angle of Inclination Output Acceleration vs. Angle of Inclination
Single Axis Dual Axis
 Sensitivity equal over entire 360° range
 Removes ambiguity beyond ±90°
X-Axis
Y-Axis

27. ADXL203 Dual Axis Accelerometer
27
 1 mg resolution for BW = 60 Hz
 700 µA current @ 5 V

28. CN0189: Tilt Measurement Using a Dual Axis
Accelerometer
28
Circuit features
 Dual axis tilt measurement
 0.5° accuracy over 360° arc
Circuit benefits
 Single supply
 Low power
 Conditioning circuits for ADXL203
outputs
Target Applications Key Parts Used Interface/Connectivity
Medical
Consumer
Industrial
ADXL203
AD8608
AD7887
SPI (AD7887)
SDP-S (EVAL-CN0189-SDPZ)
USB (EVAL-SDP-CS1Z)

29. CN0189 Dual Axis Tilt Measurement Circuit
29
AD7887 ADC
■ 12-bit, 125 kSPS SAR
■ 850 µA current @ 5 V
 AD8608 Quad Op Amp
■ 65 µV input offset voltage
■ 1 pA input bias current
■ 4 mA quiescent current
0.5 Hz BW

30. Output Error for arcsin(X), arccos(Y), and
arctan(X/Y) Calculations
30
OUTPUT = arcsin(X)
OUTPUT = arccos(Y)
OUTPUT = arctan(X/Y)
Error increases at ±90°
Error increases at 0°
Uniform error distribution

31. Tilt Measurement Using Dual Axis
Accelerometer (CN0189 Block Diagram)
31
ADXL203
DUAL AXIS
ACCELEROMETER
AD8608
QUAD OP AMP
SIGNAL
CONDITIONING
AD7887
2-CHANNEL
12-BIT, 125kSPS
SAR ADC
SYSTEM
DEMONSTRATION
PLATFORM
(SDP)
EVAL-SDP-CB1Z
PC
USB
X
Y
X
Y
CN0189 EVALUATION BOARD (EVAL-CN0189-SDPZ)

32. CN0189 Dual Axis Tilt Measurement Hardware
and Demonstration Software
32
SDP-S BOARD
POWER CONNECTOR
SOFTWARE OUTPUT DISPLAYEVAL-CN0189-SDPZ
 Complete design files
■ Schematic
■ Bill of Material
■ PADs layout
■ Gerber files
■ Assembly drawing

33. Precision Load Cell (Weigh Scales)
 Wheatstone bridge solutions
 Low level signal conditioning issues
 High common-mode voltage with respect to signal voltage
 Weigh scale system requirements
 Understanding noise-free code resolution
 ΣΔ ADC vs. SAR ADC
 High performance instrumentation amp solution (CN0216)
 High resolution ΣΔ integrated solution (CN0102)
33

34. Resistance-Based Sensor Examples
34
Strain gages 120 Ω, 350 Ω, 3500 Ω
Weigh scale load cells 350 Ω to 3500 Ω
Pressure sensors 350 Ω to 3500 Ω
Relative humidity 100 kΩ to 10 MΩ
Resistance temperature devices (RTDs) 100 Ω, 1000 Ω
Thermistors 100 Ω to 10 MΩ

35. VO
R4
R1
R3
R2
VB
VO
R
R R
VB
R
R R
VB



1
1 4
2
2 3








 






R
R
R
R
R
R
R
R
VB
1
4
2
3
1
1
4
1
2
3
AT BALANCE,
VO IF
R
R
R
R
 0
1
4
2
3
+ -
Wheatstone Bridge for Precision Resistance
Measurements
35

36. Output Voltage and Linearity Error for Constant
Voltage Drive Bridges
36
R R
R R+DR
R+DR
R+DR R+DR R+DR
R−DR R+DR R−DRR R
R R−DR
VB VB VB VB
VO
VO VO
VO
(A) Single-Element
Varying
(B) Two-Element
Varying (1)
(C) Two-Element
Varying (2)
(D) All-Element
Varying
Linearity
Error:
VO:
0.5%/% 0.5%/% 0 0
VB
4
DR
DR
2
R +
VB
2
DR
DR
2
R +
VB
2
DR
R
VB
DR
R
R

37. R R
R R+DR
R+DR
R+DR R+DR R+DR
R−DR R+DR R−DRR R
R RDR
VO
VO VO
VO
IB IB IB IB
VO:
Linearity
Error:
0.25%/% 0 0 0
IBR
4
DR
DR
4
R +
IB
2
DR IB DRIB
2
DR
(A) Single-Element
Varying
(B) Two-Element
Varying (1)
(C) Two-Element
Varying (2)
(D) All-Element
Varying
R
Output Voltage and Linearity Error for Constant
Current Drive Bridges
37

38. Kelvin (4-Wire) Sensing Minimizes Errors
Due to Lead Resistance for Voltage Excitation
38
6-LEAD
BRIDGE
RLEAD
RLEAD
+SENSE
– SENSE
+FORCE
– FORCE
+
+
+VB
–
–
VO

39. 4-LEAD
BRIDGE
RLEAD
+
–RLEAD
RSENSE
VREF
VO
I
I
I
I =
VREF
RSENSE
Constant Current Excitation also
Minimizes Wiring Resistance Errors
39

40. ADC
Architectures, Applications, Resolution, Sampli
ng Rates
40
10 100 1k 10k 100k 1M 10M 100M 1G
8
10
12
14
16
18
20
22
24
S-D
SAR
PIPELINE
INDUSTRIAL
MEASUREMENT
DATA ACQUISITION
HIGH SPEED
INSTRUMENTATION,
VIDEO, IF SAMPLING,
SOFTWARE RADIO
SAMPLING RATE (Hz)
APPROXIMATE
STATE-OF-THE-ART
(2013)
RESOLUTION

41. SAR vs. Sigma-Delta Comparison
41
Successive approximation
(SAR)
 Fast settling, ideal for multiplexing
 Data available immediately after
conversion (no "pipeline" delay)
 Easy to use (minimal programming)
 Requires external in-amp
 Has 1/f noise (need lots of
external filtering)
 Analog filter can be difficult
Sigma-Delta
 Digital filter limits settling
 More difficult to use (some
programming required)
 Some have internal PGA
 Some have chopping (removes
1/f noise)
 Internal digital filter (removes
power line noise)
 Oversampling relaxes requirement
on analog filter

42. Sigma-Delta Concepts: Oversampling, Digital
Filtering, Noise Shaping, and Decimation
42
fs
2
fs
Kfs
2
Kfs
Kfs
Kfs
2
fs
2
fs
2
DIGITAL FILTER
REMOVED NOISE
REMOVED NOISE
QUANTIZATION
NOISE = q / 12
q = 1 LSBADC
ADC
DIGITAL
FILTER
SD
MOD
DIGITAL
FILTER
fs
Kfs
Kfs
DEC
fs
NYQUIST
OPERATION
OVERSAMPLING
+ DIGITAL FILTER
+ DECIMATION
OVERSAMPLING
+ NOISE SHAPING
+ DIGITAL FILTER
+ DECIMATION
A
B
C
DEC
fs

43. First-Order Sigma-Delta ADC
43
  +
_
+VREF
–VREF
DIGITAL
FILTER
AND
DECIMATOR
+
_
CLOCK
Kfs
VIN
N-BITS
fs
fs
A
B
1-BIT DATA
STREAM1-BIT
DAC
LATCHED
COMPARATOR
(1-BIT ADC)
1-BIT,
Kfs
Ʃ-∆ MODULATOR
INTEGRATOR

44. Sigma-Delta ADC Architecture Benefits
High resolution
 24 bits, no missing codes
 22 bits, effective resolution (RMS)
 19 bits, noise-free code resolution (peak-to-peak)
 On-chip PGAs
High accuracy
 INL 2 ppm of full-scale ~ 1 LSB in 19 bits
 Gain drift 0.5ppm/°C
More digital, less analog
 Programmable balance between speed  resolution
Oversampling and digital filtering
 50 Hz/60 Hz rejection
 High oversampling rate simplifies antialiasing filter
Wide dynamic range
Low cost
44

45. Typical Applications of High Resolution
Sigma-Delta ADCs
Process control
 4 mA to 20 mA
Sensors
 Weigh scale
 Pressure
 Temperature
Instrumentation
 Gas monitoring
 Portable instrumentation
 Medical instrumentation
45
WEIGH SCALE

46. Precision Weigh Scales-Industrial and
High Precision Commercial
46
Laboratory scales
Process control
 Hopper scales
 Conveyor scales
Stock control
 Counting scales
Retail scales

47. Weigh Scale Product Definition
47
Capacity 2 kg
Sensitivity 0.1 g
Other features
 Accuracy 0.1 %
 Linearity ±0.1 g
 Temperature drift (±20 ppm at
10°C ~ 30°C)
 Data rate 5 Hz to 10 Hz
 Power (120 V AC)
 Dimensions (7.5” × 8.6” × 2.6”)
 Qualification (“legal for trade”)

48. Characteristics of Tedea Huntleigh
505H-0002-F070 Load Cell
48
Full load 2 kg
Sensitivity 2 mV/V
Excitation 5 V
Other features
 Impedance 350 W
 Total error 0.025%
 Hysteresis 0.025%
 Repeatability 0.01
 Temperature drifts 10 ppm/°C
 Overload 150%
Four strain
gages

49. Characteristics of Tedea Huntleigh
505H-0002-F070 Load Cell
49
 Full load 2 kg
 Sensitivity 2 mV/V
 Excitation 5 V
 VFS = VEXC × Sensitivity
 VFS = 5 V × 2 mV/V = 10 mV
 VCM = 2.5 V
 Full-scale voltage 10 mV
 Proportional to excitation
 “Ratiometric”

50. Input-Referred Noise of ADC Determines the
"Noise-Free Code Resolution"
50
n n+1 n+2 n+3 n+4n–1n–2n–3n–4
NUMBER OF
OCCURANCES
RMS NOISE
P-P INPUT NOISE
 6.6 × RMS NOISE
OUTPUT CODE
“GROUNDED INPUT
HISTOGRAM"

51. Performance Requirement – Resolution
51
Required: 0.1 g in 2 kg
 # Noise free counts = full-scale/p-p noise in g
 # Noise free counts = 2000 g/0.1 g = 20,000
 20,000 counts
 VFS = 10 mV at 5 V excitation
 V P-P NOISE < VFS/# counts
 VP-P NOISE < 10 mV/20,000 = 0.0005 mV
 0.5 µV p-p noise
 VRMS NOISE  VP-P NOISE/6.6
 VRMS NOISE  0.5 µV/6.6 = 0.075 µV
 75 nV RMS noise
 Noise-free bits = log2( VFS/VP-P NOISE)
 Noise-free bits = log10(VFS/VP-P NOISE) / log10(2)
 Noise-free bits = log10(10 mV/0.0005 mV)/0.3
 Noise-free bits = 14.3 (minimum)
 14.3 bits p-p in 10 mV range:
 Bits RMS = log10( VFS/VRMS NOISE)/log10(2)
 Bits RMS = log10( 10 mV/0.000075)/0.3
 17.0 bits RMS in 10 mV range

52. Definition of "Noise-Free" Code Resolution and
"Effective" Resolution
52
Effective
Resolution
= log2
Full-Scale Range
RMS Noise Bits
Noise-Free
Code Resolution
= log2
Full-Scale Range
P-P Noise
Bits
P-P Noise = 6.6 × RMS Noise
Noise-Free
Code Resolution
= log2
Full-Scale Range
6.6 × RMS Noise
Bits
= Effective Resolution – 2.72 Bits
log2 (x) =
log10 (x)
log10 (2)
=
log10 (x)
0.301

53. Terminology for Resolution Based on Peak-to-
Peak and RMS Noise
Peak-to-peak noise:
 Noise-free code resolution
 Noise-free bits
 Flicker-free bits
 Peak-to-peak resolution
RMS noise:
 Effective resolution
 RMS resolution
 The term "Effective Number of Bits" (ENOB) applies to high
speed ADCs with sine wave inputs:
ENOB = log2 (RMS value of FS sine wave/RMS noise)
This should not be confused with "Effective Resolution"
53

54. Options for Conditioning Load Cell Outputs
54
+
−
+
−
+
−
+
−
+
−
A:
EXTERNAL IN-AMP
B:
DIFFERENTIAL INPUT ADC
EXTERNAL IN-AMP
(SEE CN0216)
C:
DIFFERENTIAL INPUT ADC
INTERNAL IN-AMP OR PGA
(SEE CN0102)
ADC
SAR or Σ-Δ
RG
RG
VCM
LOAD
CELL
LOAD
CELL
LOAD
CELL
IN-AMP
FUNNEL
AMP (AD8475)
10mV
FS
10mV
FS
10mV
FS
ADC
SAR or Σ-Δ
ADC
SAR or Σ-Δ
ADC
Σ-Δ
PGA
~12
NOISE-FREE BITS
FOR 10mV FS
~12
NOISE-FREE BITS
FOR 10mV FS
15
NOISE-FREE BITS
FOR 10mV FS
16
NOISE-FREE BITS
FOR 10mV FS
SEE CN0251)
LOW NOISE
OP AMPS

55. CN0216: Load Cell Signal Conditioning with
Differential Input ADC and External In-Amp
Circuit features
 Gain of 375 low noise in-amp
 15.3 noise-free bits of resolution
Circuit benefits
 Precision load cell conditioning
 Zero-drift in-amp
 Single +5 V operation
Inputs
 10 mV full-scale
55
Target Applications Key Parts Used Interface/Connectivity
Load cell
Weigh scales
AD7791
ADA4528-1
ADP3301
SPI (AD7791)
SDP (EVAL-CN0216-SDPZ)
USB (EVAL-SDP-CB1Z)

56. CN0216: Load Cell Conditioning with
Differential Input ADC and External In-Amp
56
G = 375
FS = 10mV
FS = 3.75V
INPUT RANGE = 10V p-p
1 LSB = 10V/224 = 0.596µV
24-BIT
Σ-Δ ADC
BW = 4.3Hz DIFF BW = 8Hz
CM BW = 160Hz

57. CN0216 Noise Performance
57
 Data rate = 9.5 Hz
 VP-P NOISE = 159 counts × 0.596 µV = 94.8 µV
 VFS = 3.75 V
 Noise-free counts = VFS / VP-P NOISE
= 3.75 V/94.8 µV
= 39,557
 Noise-free bits = log2(39,557)
= 15.3 bits

58. CN0216 Evaluation Board and Software
58
Complete design files
 Schematic
 Bill of material
 PADs layout
 Gerber files
 Assembly drawing

59. AD7190, 24-Bit Sigma-Delta ADC: Weigh Scale
with Ratiometric Processing
59
IN+
IN-
OUT- OUT+
+5V
2mV/V
SENSITIVITY
Load cell:
■ 2 mV/V typically => with +5 V excitation, full-scale signal from load cell = 10 mV.
AD7190
■ With VREF = 5 V, gain = 128, full-scale signal = ±40 mV (80 mV p-p).
■ 12.5% of range used by load cell signal (10 mV ÷ 80 mV = 0.125).
■ The load cell has an offset (~50%) and full-scale error (~±20%). The wider range
available from the AD7190 prevents the offset and full-scale error from overloading
the AD7190.
■ Ratiometric operation eliminates need for external voltage reference.

60. AD7190 Sigma-Delta System On-Chip Features
Analog input buffer options
 Drives Σ-Δ modulator, reduces dynamic input current
Differential AIN, REFIN
 Ratiometric configuration eliminates need for accurate
reference
Multiplexer
PGA
Calibrations
 Self calibration, system calibration, auto calibration
Chopping options
 No offset and offset drifts
 Minimizes effects of parasitic thermocouples
60

61. CN0102: Precision Weigh Scale System
Circuit features
 Integrated solution with PGA
 16.8 noise-free bits
Circuit benefits
 Single supply
 Optimized for weigh scales
Inputs
 10 mV full-scale
61
Target Applications Key Parts Used Interface/Connectivity
Weigh scales
Load cells
AD7190
ADP3303
SPI (AD7190)
USB (EVAL-AD7190EBZ)
EVAL-AD7190EBZ

62. CN0102 Precision Weigh Scale System
62

63. AD7190 Sinc4 Filter Response, 50 Hz Output
Data Rate
63

64. AD7190 Noise and Resolution, Sinc4
Filter, Chop Disabled
64
For G = 128
VREF = 5 V,
FS = 80 mV p-p
17.5
for
10 mV p-p
Only using 10 mV out of 80 mV range

65. CN0102 Load Cell Test Results, 500 Samples
65
System resolution with load cell connected
 Load cell: full-scale output = 10 mV (2 mV/V sensitivity, VEXC = 5 V)
 Measured RMS noise = 12 nV at 4.7 Hz data rate (G = 128)
 Measured peak-to-peak noise = 88 nV
 Noise-free counts = {full-scale output/peak-to-peak noise}
= 10 mV/88 nV = 113,600
 Noise-free resolution: log2 (113,600) = 16.8 bits
Compared to 17.5 bits for AD7190 alone
 If a 2 kg load cell is used, resolution is 2000 g/113,600 = 0.02 g

66. CN0102 Evaluation Board and Load Cell
66
EVAL-AD7190EBZ
Software Display
 Complete design files
 Schematic
 Bill of material
 PADs layout
 Gerber files
 Assembly drawing

67. Tweet it out! @ADI_News #ADIDC13
What We Covered
Fundamentals of making complex impedance measurements using
integrated solutions (CN0217)
 Applications
 Extending the range of measurement using analog front end circuit
 Measurement results and applications
Tilt measurements using dual axis accelerometers (CN0189)
 Applications
 Advantages of dual axis vs. single axis
 Accelerometer conditioning circuits
Precision load cells (weigh scales) (CN0216, CN0102)
 Applications and requirements
 Bridge fundamentals
 Sigma-delta ADC fundamentals
 Noise considerations and definition of noise-free code resolution
 Solution using external in-amp
 Solution using integrated PGA
67

68. Tweet it out! @ADI_News #ADIDC13
Visit the Impedance Measurement Demo in the
Exhibition Room
Measuring complex impedances with the AD5933
68
This demo board is available for purchase:
www.analog.com/DC13-hardware
SOFTWARE OUTPUT DISPLAY

69. Tweet it out! @ADI_News #ADIDC13
Visit the Tilt Measurement Demo in the
Exhibition Room
69
Measure tilt using the ADXL203
dual axis accelerometer
This demo board is available for purchase:
www.analog.com/DC13-hardware
SDP-S BOARDSOFTWARE OUTPUT DISPLAY EVAL-CN0189-SDPZ

70. Tweet it out! @ADI_News #ADIDC13
Visit the Weigh Scale Demo in the Exhibition
Room
70
Measure weights from
0.1 g to 2000 g
This demo board is available for purchase:
www.analog.com/DC13-hardware
SOFTWARE OUTPUT DISPLAY
EVAL-CN0216-SDPZ
SDP BOARD

71. Tweet it out! @ADI_News #ADIDC13
Design Resources Covered in this Session
Design tools and resources:
71
Name Description URL
AD5933/AD5934
Demonstration and
Design Tool
Demonstrates impedance
measurement using the
AD5933/AD5934
http://designtools.analog.com/
dt/ad593x/ad593x.html
CN0189 FMC-SDP
Interposer and
Evaluation Board/
Xilinx KC705
Reference Design
Using the EVAL-CN0189-SDPZ
evaluation board, together with the
Xilinx® KC705 FPGA board, the Xilinx
Embedded Development Kit (EDK),
and the Micrium µC-Probe run-time
monitoring tool.
http://wiki.analog.com/resourc
es/fpga/xilinx/interposer/cn018
9
ADXL203 Simulink®
Model
Simulink model http://www.analog.com/en/me
ms-sensors/mems-inertial-
sensors/adxl203/products/tool
s-software-simulation-
models/index.html?location=to
ols-software
CN0216 BeMicro
FPGA
BeMicro FPGA for CN0216
with Nios driver
http://wiki.analog.com/resourc
es/fpga/altera/bemicro/cn0216

72. Tweet it out! @ADI_News #ADIDC13
Design Resources Covered in this Session-2
72
Name Description URL
Signal Chain
Designer
Complete engineering
design environment
http://www.analog.com/scd
AD7190 Tools Tools, software, and
simulation models
http://www.analog.com/en/analog-to-digital-
converters/ad-
converters/ad7190/products/tools-software-
simulation-models/index.html?location=tools-
software
AD7887 Tools Tools, software, and
simulation models
http://www.analog.com/en/analog-to-digital-
converters/ad-
converters/ad7887/products/tools-software-
simulation-models/index.html?location=tools-
software
AD7791 Tools Tools, software, and
simulation models
http://www.analog.com/en/analog-to-digital-
converters/ad-
converters/ad7791/products/tools-software-
simulation-models/index.html?location=tools-
software

73. Tweet it out! @ADI_News #ADIDC13
Design Resources Covered in this Session-3
73
Ask technical questions and exchange ideas online in our
EngineerZone® Support Community
 Choose a technology area from the homepage:
 ez.analog.com
 Access the Design Conference community here:
 www.analog.com/DC13community

74. Tweet it out! @ADI_News #ADIDC13
Selection Table of Products Covered Today
74
Part number Description
AD5933 1 MSPS, 12-bit impedance converter, network analyzer
AD8606 Precision, low noise, RRIO, CMOS op amp (dual)
ADG849 3 V/5 V CMOS 0.5 Ω SPDT switch in SC70
AD8221 Precision instrumentation amplifier
AD820 Single-supply, rail-to-rail, low power, FET input op amp
ADXL203 Precision ±1.7 g, ±5 g, ±18 g dual axis iMEMS accelerometer
AD8608 Precision, low noise, RRIO, CMOS op amp (quad)
AD7887 2.7 V to 5.25 V, micropower, 2-channel, 125 kSPS, 12-bit ADC in
8-lead MSOP

75. Tweet it out! @ADI_News #ADIDC13
Selection Table of Products Covered Today-2
75
Part number Description
AD7791 24-bit, single-channel, ultralow power, Ʃ-∆ ADC
ADA4528-1 5.0 V ultralow noise, zero-drift, RRIO, single op amp
ADP3301 High accuracy anyCAP® 100 mA low dropout linear regulator
ADP7190 4.8 kHz ultralow noise 24-bit Ʃ-∆ ADC with PGA
ADP3303 High accuracy anyCAP 200 mA low dropout linear regulator

76. Tweet it out! @ADI_News #ADIDC13
References-1
Circuit Notes
 CN0217, Impedance Measurements
 www.analog.com/CN0217
 CN0189, Tilt Measurements
 www.analog.com/CN0189
 CN0216, Precision Weigh Scale, External In-Amp
 www.analog.com/CN0216
 CN0102, Precision Weigh Scale, Internal PGA
 www.analog.com/CN0102
 CN0251, A Flexible 4-Channel Analog Front End for Wide Dynamic Range
Signal Conditioning
 www.analog.com/CN0251
 CN0260, Oversampled SAR ADC with PGA
 www.analog.com/CN0260
 CN0189, 4 mA to 20 mA Loop-Powered Pressure Sensor Transmitter
 www.analog.com/CN0189
76

77. Tweet it out! @ADI_News #ADIDC13
References-2
Mini Tutorials
 MT-004, ADC Input Noise
 www.analog.com/MT-004
 MT-021, Successive Approximation (SAR) ADCs
 www.analog.com/MT-021
 MT-022, Sigma-Delta ADC Basics
 www.analog.com/MT-022
 MT-023, Sigma-Delta ADC Advanced Concepts
 www.analog.com/MT-023
 MT-061, In-Amp Basics
 www.analog.com/MT-061
 MT-062, Two Op Amp In-Amp
 www.analog.com/MT-062
 MT-063, Three Op Amp In-Amp
 www.analog.com/MT-063
77

78. Tweet it out! @ADI_News #ADIDC13
References-3
Mini Tutorials
 MT-064, In-Amp DC Errors
 www.analog.com/MT-064
 MT-065, In-Amp Noise
 www.analog.com/MT-065
 MT-066, In Amp Bridge Circuit Error Analysis
 www.analog.com/MT-066
 MT-069, In-Amp Overvoltage Protection
 www.analog.com/MT-069
 MT-070, In-Amp Input RFI Protection
 www.analog.com/MT-070
78

79. Tweet it out! @ADI_News #ADIDC13
References-4
Reference Books
 Sensor Signal Conditioning
 www.analog.com/sensor_signal_conditioning
 Analog-Digital Conversion
 http://www.analog.com/library/analogDialogue/archives/39-
06/data_conversion_handbook.html
 Op Amp Applications
 http://www.analog.com/library/analogDialogue/archives/39-
05/op_amp_applications_handbook.html
 Linear Circuit Design
 http://www.analog.com/library/analogDialogue/archives/43-
09/linear_circuit_design_handbook.html
 Instrumentation Amplifier Handbook
 http://www.analog.com/en/specialty-amplifiers/instrumentation-
amplifiers/products/design-
handbooks/cu_dh_designers_guide_to_instrumentation_amps/resources/fca.
html
79