motion sensing and data acquisition in high temperature environments … · 2017. 2. 15. · specs...
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MOTION SENSING AND DATA
ACQUISITION IN HIGH
TEMPERATURE ENVIRONMENTS
Jeff Watson
jeffrey.watson@analog.com
Maithil Pachchigar
Venkat Chandrasekaran
Analog Devices, Inc.
High Temperature Applications
Oil and Gas Exploration Avionics
Under-hood Automotive Heavy Industrial Processes Geothermal
High Temperature Applications
Oil and Gas Exploration Avionics
Under-hood Automotive Heavy Industrial Processes Geothermal
Common Signal Processing Needs:
• Multiple Sensors
• Precision Data Acquisition
• Low Power
• Small Form Factor
• Rugged Packaging
What is “High Temperature”, Anyway?
0-40-55 70
85
125 150 175 210
COMMERCIAL
INDUSTRIAL
MILLITARY/EP
AUTOMOTIVE
HT PLASTIC
HT CERAMIC
Temperature °C
Using Standard Temp ICs at Elevated
Temperatures is Problematic!
Process Changes
Expensive Qualification
Die Availability
Package Type
Package ReliabilityPerformance
Electromigration
Failure Analysis
HT Process Flow Highlights
Design
• Process Selection
• HT Design Practices
• Electromigration / Current Density
Characterization
• Design Verification
• HT Datasheet Specifications
• Multiple Lots
Qualification
• HT Operating Life
• HT Storage
• Temp Cycle
• MIL-STD-883 Group D Mechanical
• Shock
• Vibe
• Accel
• Seal
• Moisture
• ESD
• Latchup
Production Test
• HT Probe 175C
• HT Package
• 150C Plastic
• 190+C Hermetic
How Accelerometers Measure Acceleration
F = kxF = mA
Am
k
x
kx = mA x = A
known
At constant velocity, the spring does not stretch.
�
�
Typical displacement in
a low-g accelerometer
~10 nm/g
Measuring the Position of the Proof Mass
X
Y
�Differential capacitance used to pick off motion of mass
� C1 and C2 is the capacitance between the mass and a set of fixed fingers
� Keep monitoring (C1 – C2) to determine if the mass has moved in the X-axis
C1 C2
Gyro Building Blocks
x
x
x
xMass with
velocity
• The “resonator” (also referred to
as the moving mass) which
generates a force any time we
rotate it
• The “Coriolis” channel which is
the accelerometer that surrounds
the moving mass, and its sole
purpose is to detect the force
generated by the resonator
• Complicated couplingCouplingForce on
XL
Gyroscope Circuit Architecture
• Surface micro-machined gyros made using ADI specific “Integrated” BiMOS process
• “Integrated” means beams and circuits are made side by side on the same piece of Silicon
• Beam structures are made out of 4 um thick poly-silicon
• Signal conditioning circuitry also large geometry
• Single die solution (BiMOS die with both beams and circuits)
• BiMOS process allows laser trim
Sensor SpecificationsParameter Value Units
Supply Voltage 5.0±0.25 V
Temperature Range −40 to 175 °C
Quiescent Current 3.5 mA
Sensitivity 1.0 mV/°/s
Dynamic Range±2000
(extendable to ±5000)°/s
Bandwidth (±3dB) 2000 Hz
Noise Density 0.25 °/s/√Hz
Resolution Floor - 25°C
150°C
100
150°/hr
Linear-g sensitivity 0.1 °/s/g
Vibration rectification
25g rms, 50Hz to 5kHz 0.0006 °/s/g2
Bias Stability – Allen Variance
• Bias stability is often considered the most important parameter
• Measured by Allen Variance, which is function of averaging time
• Allan Variance plot shows the bias uncertainty between successive averaging periods
• Initial slope corresponds to broadband noise
• Longer time asymptote of the plot is equivalent to the resolution floor
Other Accuracy Considerations
�But Wait! It isn’t that simple. Other “real world” error sources
�Null Bias (Offset)
�Sensitivity Error (Gain)
�Variation over temperature
�For this reason there is a temp sensor on board for calibration
�Temperature hysteresis is very low, on order of 0.075% FS
�Plus, all of these other error sources could be dwarfed by effects of linear acceleration (vibration)
Error Due to Linear Acceleration and Vibe
� Ideally a gyroscope would be sensitive only to rotation rate
� In reality all gyros have sensitivity to acceleration due to asymmetry of mechanical design and other micromachining inaccuracies
�Most significant are sensitivity to linear acceleration (g sensitivity) and vibration reification (g2 sensitivity)
�Also shock events can saturate sensor response
�These errors can easily be largest in error budget when operating in a harsh environment
Dual Resonator Design
x
x
x
xMass
with
velocity
Resonator
Moving
RightForce on
XL if
Rotation
occurred
x
x
x
xMass
with
velocity
Second
Resonator
Moving Left Force on
XL if
Rotation
occurred
Quad Resonator Design
Linear-g sensitivity 0.1 °/s/g
Vibration rectification
25g rms, 50Hz to 5kHz 0.0006 °/s/g2
Temperature Compensation
• To operate over the wide temp range best performance is realized if offset and sensitivity are temperature compensated
• On chip temp sensor to facilitate this
• Need null voltage, sensitivity and temp sensor output for each cal point
• The variation over temp is non-linear, so at least six temp cal points may be needed
Device Calibration – Null Output (Offset)
Offset over temperature Residual error after 5th order
polynomial correction
Device Calibration – Sensitivity
Sensitivity over temperatureResidual error after 5th order
polynomial correction
Package – High Temperature Compliance
�Hermetic Ceramic Package � Established Assembly BOM
�Solder Seal Lid
�Mono-metallic wire bond (Al-Al)
�Au plated leads
�Through-hole leads
Package – Vertical Mount Ceramic
Application Example:
Downhole Drilling
• Accurate, robust measure of rotation needed
• Needed now more than ever with focus on drilling dynamics and abuse measurements
• Magnetometers can be used but subject to interference and problematic in high shock/vibe
• Need high temperature operation
Downhole Drilling – Stick-Slip
Drill Bit Stuck
Continues to
Rotate at Surface
…Leads to cyclical violent motion when drill string breaks free
Downhole Drilling – Stick-Slip
Downhole Tool Signal Chain
HT Data Acquisition Reference DesignOptimized for low power/low voltage with 2.5V reference
AD7981
ADR225 AD8634VSUPPLY Connections for
ADC, Amp, Reference
Space for
passive
filter
AD8634
SPI PMOD to
connect up
outside the oven
Solder links to allow user
to bypass the area
SMA connector
Space for
passive
filter
Specs of Reference Design
• Single Channel Data Acquisition Building Block
• 16 bit, 600kSPS SAR ADC
• 2.5V Micro-power Voltage Reference
• Dual Precision Op Amp– ADC Driver
– Voltage Reference Buffer
• PMOD SPI Digital Output
• High Temperature compliant PCB
• High Temperature passive components
• Tested and characterized over temperature
AD7981 175C/210C 16b 600KSPS SAR ADC
– 16-bit resolution with no missing
codes
– Throughput: 600 KSPS
– Low power dissipation scalable to
sample rate
– Pseudo differential analog input
range
– Serial SPI Interface, chainable
– Qualified for minimum 1000 hours
operation at max temp
– High temperature robust packaging
– 10 lead MSOP, BBFP or KGD
AD7981
REF
GND
VDD
IN+
IN–
VIO
SDI
SCK
SDO
CNV
1.8V TO 5.0V
3- OR 4-WIRE INTERFACE
(SPI, DAISY CHAIN, CS)
2.5V TO 5V 2.5V
0 TO VREF
ADC Analog Front End Design
Voltage Reference Considerations
High Temp Packaging Considerations
Wire Bond Integrity at Elevated Temp
• Au/Al wire bonding is industry standard
interconnect
• Au and Al fuse at the interface to form an
inter-metallic compound (IMC)
• IMC continues to grow by diffusion.
• Growth rate is temperature dependant,
accelerated at higher temp.
• Can be modelled with the Arrhenius equation
• Bond failures present as high resistance
(voiding) or open (separation)
• Halogens in mould compound promote
corrosion at Au-IMC boundary and accelerate
failure further
• Mono-metallic system is preferred!
HT Plastic Wire Bond Integrity
• Over-pad-metallization (OPM): NiPdAu
plated layers on Al Pad prevent AuAl
IMC growth
• Halogen-free BOM prevents corrosion
Au/Al Bond post 500hrs at 195°C Au/OPM Bond post 6000hrs at 195°C
Si Substrate
Al
Au
Ni
Pd
Nickel Palladium Gold (NiPdAu)
High Temp Packaging Options
• Hermetic Ceramic Package
• Bottom Brazed Flatpack
• SMT “dead bug” lead forming
• Al-Al wire bond (Mono-Metallic)
• 210C for 1000 hours
• Plastic MSOP
• Au-Au wire bond (Mono-Metallic)
• NiPdAu lead Frame
• Halide-Free BOM
• SMT and Small Footprint
• 175C for 1000 hours
PCB Design Considerations
• Laminate – Polyimide High Tg (240C+)
• Surface Finish (Intermetallics)
• High Melting Point Solder
– Lead vs Lead Free
• Hermetically Sealed Multi Chip Modules
– Require Die Availability
Lab Characterization Test Setup
HT Data Acquisition
Board (DUT)
DC Power Supplies
Audio Precision
SYS-2522
+5V, 2.5V, GND
Analog
InputSPI DIGITAL
OUT (PMOD)
PMOD InterposerSDP
Board
USB PC with
FFT Analysis
Software
SDP 120 PIN
CONNECTOR
AC performance with 1KHz input tone, 580 kSPS, 25°C
AC performance with 1KHz input tone, 580 kSPS, 175°C
83
83.5
84
84.5
85
85.5
86
86.5
0 25 50 75 100 125 150 175 200
SNR
(d
B)
Temperature (°C)
Signal to Noise Ratio
Total Harmonic Distortion
-105
-104
-103
-102
-101
-100
-99
-98
0 25 50 75 100 125 150 175 200T
HD
(d
B)
Temperature (°C)
For Further Information
• www.analog.com/hightemp
• “High Temperature Electronics Pose Design
and Reliability Challenges”
• “Harsh Environments Conquered – Precision
Components for Extreme High Temperatures”
• HiTEN Conference July 2015, Cambridge UK
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