Σ−∆ CDC – Direct Interface to Cap. Sensors Σ−∆CDC – Direct Interface to Cap. Sensors...
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1 Σ−∆ CDC – Direct Interface to Cap. Sensors Capacitive sensor signal chain C to V Converter Discrete or ASIC Solution C => V ADC HOST (digital) CDC HOST (digital) Capacitance to Digital Converter Direct Capacitive Input Standard Single Chip Solution
Transcript of Σ−∆ CDC – Direct Interface to Cap. Sensors Σ−∆CDC – Direct Interface to Cap. Sensors...
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Σ−∆ CDC – Direct Interface to Cap. Sensors
Capacitive sensor signal chainC to V ConverterDiscrete or ASIC Solution
C => V ADC HOST(digital)
CDC HOST(digital)
Capacitance to Digital ConverterDirect Capacitive InputStandard Single Chip Solution
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Σ−∆ CDC – Architecture
VREF(+)
Integrator Comparator
CIN ⊗⊗
⊗⊗
⊗⊗
⊗⊗VREF(-)
VIN(+)
VIN(-)
CREF
CINT
0100110DigitalFilter
CSENSOROff - Chip
Excitation Voltage
Σ−∆ Modulator – Charge balancing circuitΣ−∆ ADC – Variable input Voltage, Fixed on chip Capacitance Σ−∆ CDC – Fixed excitation Voltage, Variable External Capacitance
Σ−∆ Inherent features – High Resolution, High Linearity, …
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Σ−∆ Converters – High Performance System On Chip
21-bit Eff. Resolution
4 aF Input Noise(4 x 10-18 F)
4 fF Accuracy (4 x 10-15 F)
0 to 17pF Capacitancewith ±4pF Range
±2°C Temp. SensorAux. Voltage InputCalibrationSerial Interface...
700uA Idd
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a × bC ≈ ε0 εR ———
d
Σ−∆ CDC – ApplicationsFuel Impurity, Oil Quality, Other Liquids Quality
Dielectric constant changes with oil quality
Simple capacitive sensorTemperature compensation
High resolution Σ−∆ CDC
AutomotiveIndustrialMedical
CDC
ADC Proc
essi
ng DATA
Capacitive Sensor
Temp. Sensor
Temperature Compensation
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Σ−∆ CDC – ApplicationsFuel Level, Oil Level
Size of capacitor changes with level
Simple capacitive sensorεR compensation - 2nd sensor
High resolution Σ−∆ CDC
AutomotiveIndustrial
DATA
a × bC ≈ ε0 εR ———
d
CDC
CDC
Proc
essi
ng
Capacitive Sensor
Capacitive Sensor
εR Compensation
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Σ−∆ CDC – ApplicationsPressure Sensor
a × bC ≈ ε0 εR ———
dDistance in capacitor changes with pressure
Simple capacitive sensorTemp. compensation
High resolution Σ−∆ CDC
IndustrialAutomotiveTemp.
Sensor
Pressure
Temperature Compensation
ADC Proc
essi
ng DATACDC
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a × bC ≈ ε0 εR ———
d
Σ−∆ CDC – ApplicationsHumidity Sensor
Dielectric constant changes with humidity
Ceramic Substrate εR ≈ 3Water εR ≈ 81
Simple capacitive sensorTemperature sensor−Temperature Compensation−Relative Humidity Calculation
High resolution Σ−∆ CDC
Air ConditioningEnvironmentalADC Pr
oces
sing DATA
Capacitive Sensor
CDC
Vapors exchange between Air and Ceramic Substrate
Temp. Sensor
Temperature Measurement
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Σ−∆ CDC – ApplicationsProximity Detector
a × bC ≈ ε0 εR ———
d
Electric Field changes with an object proximity
Simple capacitive sensorThreshold algorithm eliminating environmental changes
Low Cost Σ−∆ CDC
AutomotivePassive Keyless entry
THRESHOLD
TRIGGER
Capacitive Sensor
CDC
Threshold Algorithm
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Σ−∆ CDC – DemoProximity Sensor
Simple Proximity SensorTwo PCB strips
CDC Demo ChipBased on ADuC824
GND
DIGITALFILTER
TXD
VDD
HOSTSYSTEM
(PC)
Σ-∆MODULATOR
CONTROLLOGIC
EXCITATION
CDC DEMO CHIP
PROXIMITY DEMO SENSOR
(uC SOFTWAREIMPLEMENTED
FOR THE DEMO)
THRESHOLDD1“DISPLAY”
5VREGULATOR 9V
BATTERY
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AD7745 – the First 24-Bit Σ−∆ CDC
Capacitive Input Input Range ±4pF (changing)Offset Removal up to 2 x 17pFResolution 16-bit p-p @ 16.6HzAccuracy 2fF (factory calibrated)Data Rate10 Hz to 120 Hz
On chip Temp Sensor 0.1°C Resolution± 2°C Accuracy
Voltage Input24-bit data3uV rms Input NoiseOn-chip / External VREF
FeaturesI2C®-Compatible InterfaceSingle-supply 3 or 5V / 1mAOperating Temp. -40°C ..+125°CPackage: 16-lead TSSOP
SCLCLOCKGENERATORTEMPSENSOREXC1MUXDIGITALFILTERVDD24-BITΣ-∆MODULATORI2CSERIALINTERFACECAPDACEXCITATIONAD7745CIN1(+)CIN1(-)CAPDACVIN(+)VIN(-)GNDEXC2CONTROLLOGICCALIBRATIONRDYREFIN(+)REFIN(-)VOLTAGEREFERENCESDA
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AD7745 – Differential Capacitive Input
CLOCKGENERATORTEMPSENSORGNDEXCMUXDIGITALFILTERSCLSDAVDDHOSTSYSTEM24-BITΣ-∆MODULATORI2CSERIALINTERFACECAPDACEXCITATIONAD77450.1uF10uF+REFIN+3V/+5VPOWERSUPPLYCIN(+)CIN(-)CAPDACDIFFERENTIALCAPACITIVESENSORVIN(+)VIN(-)
Confidential for Distributors only
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AD7745 – Voltage InputExample: External Thermistor or RTD
Voltage channel can take temperature measurements close
to the cap sensor to allow for temperature compensation
Confidential for Distributors only
SCLSDAHOSTSYSTEM0.1uF10uF++3V/+5VPOWERSUPPLYRREFRTDCAPACITIVESENSORRDYCLOCKGENERATORTEMPSENSOREXC1MUXDIGITALFILTERVDD24-BITΣ-∆MODULATORI2CSERIALINTERFACECAPDACEXCITATIONAD7745CIN1(+)CIN1(-)CAPDACVIN(+)VIN(-)GNDREFIN(-)EXC2CONTROLLOGICCALIBRATIONRDYREFIN(+)VOLTAGEREFERENCE
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AD7747 – Grounded Sensor1 Differential Input for Grounded Capacitor
GroundedSensor Active AC Shield
SCLSDAVDDGNDRDYCLOCKGENERATORTEMPSENSORSHLD(+)MUXDIGITALFILTERI2CSERIALINTERFACECAPDAC1EXCITATIONAD7747CIN(+)VIN(+)VIN(-)24-BITΣ-∆MODULATORCAPDAC2SHLD(-)CIN(-)REFIN(+)REFIN(-)CONTROLLOGICCALIBRATIONVOLTAGEREFERENCE
Confidential for Distributors only
