3-axis accelerometer and strain sensor
readout MEMS-based capacitive
sensors
Juan Santana
Richard van den Hoven
Imec-Holst Centre
The Netherlands
1st MEMSCON Event - 07 October 2010, Bucharest
Imec- Holst Centre
Overview
Accelerometer
Summary
•
MEMS based charge sensing
•
Accelerometers & Strain sensors
Technical Specifications
•
Programmable gain by timing control, sensitivity and
accuracy read-out
•
Low-power
•
TSMC CMOS 0.25m with operating voltage (3.0V)
•
±2 g input range, 1mg resolution
•
High linearity (1%)
•
Parasitics insensitive
Applications
•
Strain sensor
Sensor area
Accelerometers, strain sensors for structural
assessment, automotive and BAN, industrial and
healthcare
1st MEMSCON Event - 07 October 2010, Bucharest
Imec- Holst Centre
Architecture
CONTROL
V1
Novel Technique
Cs
 Integration of multiple pulses
SW4
Cin
OA
 Variable gain set by number of pulses
26
SW2
Cr
SW1
 Integrated noise proportional to √N
SW5
SW3
 Timing allows duty-cycle control
V2
VREF1
VREF2
GND
 Signal-to-noise ratio control
Architecture
 Decouples sensor from amplifier
CLK,V1,V2\
250
160
310
Reset
 Allows readout of wide range of sensors
Integrate
 Accurate sin(x)/x suppresses artifacts
Sample
Xvalid
34a
 Multiplexed output
610
Yout
Zout
Xout
Timing sequence
1st MEMSCON Event - 07 October 2010, Bucharest
Imec- Holst Centre
ASIC
ESD
System Level characteristics
 3-channel architecture
Bias stage
Y-channel
 1 Analog multiplexed buffered output
 1 Analog non-multiplexed (X channel)
 Synchronization signals available
4mm
X-channel
 Embedded filtering (sin(x)/x response)
 1 Bias voltage (VDD) and 1 clock
Z-channel
 Minimum capacitance ESD structures
MUX+buffer
+digital
2mm
1st MEMSCON Event - 07 October 2010, Bucharest
Imec- Holst Centre
Results
Accelerometer
Variable sensitivity ~N
Sensitivity (V/g)
25
20
15
10
5
0
0
300
400
Integrated Noise ~√N
Total integrated noise (V)
2500
2000
Vout [mV]
1500
1000
500
-10000
0.005
0.004
0.003
0.002
y = 0.0003x0.4206
0.001
0.000
0
-20000
200
Number of pulses
Strain sensor
-30000
100
0
10000
Strain [µstrain]
20000
30000
0
100
200
300
400
Number of pulses
1st MEMSCON Event - 07 October 2010, Bucharest
Imec- Holst Centre
Benchmarking
Parameter
Denison
Paavola
IMEC-NL
Acceleration
strain range
~±1g
ISSCC2008
±2g
Supply voltage
Power
Noise Floor
1.7-2.2V
1.5µW
1mg/√Hz
1.0V
1.5µW
704µg/√Hz
(accel.)
Non-linearity
<1%
---
Bandwidth
FOM
10Hz
1Hz
<1% (accelerometer)
<0.6% (strain sensor)
100Hz
F√(W/Hz)
8.1×10-22
µW·µg/Hz
Technology
1400
4.41×10-20
881
0.8µm CMOS
0.25µm CMOS
0.25µm CMOS
Area
----
2.25mm² c
2 mm² (active)
8 mm2
±2.5g
±20,000µe
Variable gain
3.0V
15µW
70µg/√Hz
State-of-the-art readout architectures
1st MEMSCON Event - 07 October 2010, Bucharest
Imec- Holst Centre
Conclusions
 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
1st MEMSCON Event - 07 October 2010, Bucharest
Company