Ultra Low Power Capacitive Sensor Interfaces

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Springer Science & Business Media, Jun 15, 2007 - Technology & Engineering - 104 pages
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The increasing performance of smart microsystems merging sensors, signal processing and wireless communication promises to have a pervasive impact during the coming decade. These autonomous microsystems nd applications in sport evaluation, health care, environmental monitoring and automotive s- tems. They gather data from the physical world, convert them to electrical form, compensate for interfering variables or non-linearities, and either act - rectly on them or transfer it to other systems. Most often, these sensor systems are developed for a speci c application. This approach leads to a high rec- rent design cost. A generic front-end architecture, where only the sensors and the microcontroller software are customized to the selected application, would reduce the costs signi cantly. This work presents a new generic architecture for autonomous sensor nodes. The modular design methodology provides a exible way to build a complete sensor interface out of con gurable blocks. The settings of these blocks can be optimized according to the varying needs of the application. Furthermore, the system can easily be expanded with new building blocks. The modular system is illustrated in a Generic Sensor Interface Chip (GSIC) for capa- tive sensors. Many con guration settings adapt the interface to a broad range of applications. The GSIC is optimized for ultra low power consumption. It achieves an ON-state current consumption of 40?A.
 

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Contents

INTRODUCTION
2
GENERIC ARCHITECTURES FOR AUTONOMOUS SENSORS
5
2 Multisensor microsystem
6
22 Sensor interface chip
7
23 Microcontroller
8
24 Wireless link
9
3 Modular design methodology
10
31 Programming flow
11
53 Effective number of bits
59
6 Experimental results
60
61 Pressure monitoring system
62
62 Inclination monitoring system
65
7 Performance comparison
69
8 Conclusion
70
ALGORITHM FOR OPTIMAL CONFIGURATION SETTINGS
73
21 Fullscale loss
74

32 Operational flow
13
4 Conclusion
14
GENERIC SENSOR INTERFACE CHIP
17
2 Capacitive sensors
18
3 Generic Sensor Interface Chip for capacitive sensors
20
31 Frontend architecture
21
32 CapacitancetoVoltage convertor
24
33 Chopping scheme
28
34 SC amplifier
29
35 ΣΔ modulator
33
36 Bandgap reference bias system and buffered reference voltage
42
37 Main clock clock generation circuits and LF clock
48
4 Configuration settings
51
5 Noise
53
52 Noise calculations
54
22 Programmability of Cref
75
23 Programmability of Cf
76
24 Programmability of ASC
80
25 Noise
82
3 Optimal settings
83
4 Results
84
5 Conclusion
85
PHYSICAL ACTIVITY MONITORING SYSTEM
86
3 Implementation
88
4 Conclusion
90
CONCLUSION
91
2 Suggestions for future work
93
References
95
Index
102
Copyright

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