Mixed Signal Design Examples: Capacitance to Voltage Converter & Pressure Sensors
Explore mixed signal design examples including capacitance to voltage converter, charge amplifiers, pressure sensors, and more. Understand dynamic range analysis, capacitance resolution, and the use of absolute pressure sensors as altimeters. Learn about commercial capacitive and piezoresistive pressure sensors with detailed specifications.
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Presentation Transcript
Interface design example: capacitance to voltage converter. Switched Capacitors Charge amplifier CX CXFS=100 fF P PFS=120 kPa P. Bruschi Mixed Signal Design 1
SC charge amplifier design Sensor: 80 fF CX 180 fF CR=80 fF CFS=100 fF Design choices: VR=Vdd=3.3 V (ratiometric) C2= CFS=100 fF 0 VOUT Vdd P. Bruschi Mixed Signal Design 2
Dynamic range (only kT/C contribution is analyzed) C V = FS R / DR = 2174 (66.7 dB , 11.1 bit) ( ) + + C C C 4 kT C 2 X R FS 4125 0.527 21 4 10 J kT = = 4 4 8 . 0 mV 15 C 100 10 F FS P. Bruschi Mixed Signal Design 3
Capacitance resolution C 100 fF = = = = FS . 0 045 fF 45 aF C n 2174 DR Pressure resolution P 120 kPa =DR = = FS . 0 055 kPa P n 2174 P. Bruschi Mixed Signal Design 4
Use of an absolute pressure sensor as an altimeter dp = ( , ) p T g dh h USA National Oceanic and Atmospheric Administration . 0 190284 p 44307 69 . 1 h 102325 Altitude resolution: h = = h p 5.28 m e e p 96 m /kPa 0.055 kPa P. Bruschi Mixed Signal Design 5
Example of commercial capacitive pressure sensor P. Bruschi Mixed Signal Design 6
Infineon DPS 310 - Specifications P. Bruschi Mixed Signal Design 7
Example of piezoresistive pressure sensor Freescale (now NXP) MPL3115A2 sensor I2C Digital Interface P. Bruschi Mixed Signal Design 8
MPL3115A2 Specifications 128 samples are averaged to reduce noise Accuracy is much worse than resolution, since it dependes also on the offset and other quasi-static errors P. Bruschi Mixed Signal Design 9
Example of Piezoresistive sensor: STMicroelectronics LPS225HB P. Bruschi Mixed Signal Design 10
