3-axis accelerometer and strain sensor readout mems-based capacitive sensors juan santana richard...
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3-axis accelerometer and strain sensor readout MEMS-based capacitive
sensors
Juan Santana
Richard van den Hoven
Imec-Holst Centre
The Netherlands
Imec- Holst Centre1st MEMSCON Event - 07 October 2010, Bucharest
1st MEMSCON Event - 07 October 2010, Bucharest
Overview
Summary
• MEMS based charge sensing
• Accelerometers & Strain sensors
Technical Specifications• Programmable gain by timing control, sensitivity and
accuracy read-out
• Low-power
• TSMC CMOS 0.25m with operating voltage (3.0V)
• ±2 g input range, 1mg resolution
• High linearity (1%)
• Parasitics insensitive
Applications• Accelerometers, strain sensors for structural
assessment, automotive and BAN, industrial and healthcare
Accelerometer
Sensor area
Strain sensor
Imec- Holst Centre
1st MEMSCON Event - 07 October 2010, Bucharest
Architecture
Cin
SW5
VREF2VREF1
OA
Cs
Cr
26SW2
SW3SW1
SW4
GND
V1
V2
CONTROL
CLK,V1,V2\
Reset
Yout Zout Xout
Integrate
Sample
250
160
310
Xvalid34a
610
Architecture
Timing sequence
Novel Technique
Integration of multiple pulses
Variable gain set by number of pulses
Integrated noise proportional to √N
Timing allows duty-cycle control
Signal-to-noise ratio control
Decouples sensor from amplifier
Allows readout of wide range of sensors
Accurate sin(x)/x suppresses artifacts
Multiplexed output
Imec- Holst Centre
1st MEMSCON Event - 07 October 2010, Bucharest
ASIC
2mm
Y-channel
X-channel
Z-channel
4mm
Bias stage
MUX+buffer+digital
ESDSystem Level characteristics
3-channel architecture
1 Analog multiplexed buffered output
1 Analog non-multiplexed (X channel)
Synchronization signals available
Embedded filtering (sin(x)/x response)
1 Bias voltage (VDD) and 1 clock
Minimum capacitance ESD structures
Imec- Holst Centre
1st MEMSCON Event - 07 October 2010, Bucharest
Results
0
500
1000
1500
2000
2500
-30000 -20000 -10000 0 10000 20000 30000
Vout
[mV
]
Strain [µstrain]
0
5
10
15
20
25
0 100 200 300 400
Sens
itivi
ty (V
/g)
Number of pulses
Accelerometer
Strain sensor
Variable sensitivity ~N
y = 0.0003x0.4206
0.000
0.001
0.002
0.003
0.004
0.005
0 100 200 300 400
Tota
l inte
grat
ed n
oise
(V)
Number of pulses
Integrated Noise ~√N
Imec- Holst Centre
1st MEMSCON Event - 07 October 2010, Bucharest
Benchmarking
Parameter Denison Paavola
ISSCC2008
IMEC-NL
Acceleration
strain range
~±1g ±2g ±2.5g±20,000µeVariable gain
Supply voltage 1.7-2.2V 1.0V 3.0VPower 1.5µW 1.5µW 15µWNoise Floor
(accel.)
1mg/√Hz 704µg/√Hz 70µg/√Hz
Non-linearity <1% --- <1% (accelerometer)<0.6% (strain sensor)
Bandwidth 10Hz 1Hz 100HzFOM
F√(W/Hz)
µW·µg/Hz
8.1×10-22
1400 4.41×10-20
881
Technology 0.8µm CMOS 0.25µm CMOS 0.25µm CMOS
Area ---- 2.25mm² c 2 mm² (active)8 mm2
Imec- Holst Centre
State-of-the-art readout architectures
1st MEMSCON Event - 07 October 2010, Bucharest
Conclusions
Company
Versatile architecture for MEMS-based capacitive sensors
Cost effective design requires less external components
Low Power
Sampled output relaxes demands of following stages
Embedded filtering
Novel technique to control gain and SNR of the readout
Can be extended to many other types of capacitive based sensors