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P
RELIMINARY
C
APACITANCE
TO
A
NALOG
C
ONVERTER
QT301
Capacitance to Analog Converter (CAC) IC
Patented charge-transfer conversion method
Sub-ranging Direct-to-Analog conversion
Rescaleable PWM: wide dynamic range
End-to-end calibration (gain, span) via CAL pins
100 kHz PWM
Spread spectrum acquisition bursts for low noise
Sample on demand via Sync pin
Only one external sample capacitor
SYNC
CAL_DN
SNS1
VSS
1
8
VDD
CAL_UP
PWM
SNS2
QT301
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APPLICATIONS
Fluid level sensors
Proximity sensors
Moisture detection
Position sensing
Transducer driver
Material sensors
The QT301 charge-transfer (QT) IC is a self-contained Capacitance-to-Analog-Converter (CAC) capable of detecting
femotofarad level changes in capacitance. This part is designed primarily for stand-alone instrumentation applications.
Primary applications include fluid level sensors, distance sensors, material detectors, transducer amplifiers for pressure and
humidity sensing functions, and other uses requiring quantified capacitance data.
Unlike other Quantum products, the QT301 does not process its acquired data. Its only output is raw, unprocessed data in
filterable PWM form that can be translated into an analog voltage by a simple RC network. This allows the designer to treat
the device as a CAC for measurement applications.
The PWM range is set via two inputs that control the starting and ending point of the conversion range. For example, if the
capacitance range of Cx is from 27pF to 38pF, the QT301 can be calibrated so that the PWM zero point occurs at 27pF, and
the endpoint (255) occurs at 38pF. In this way, the PWM range is optimized for the zone of interest. These calibration points
are stored in internal EEPROM and do not have to be reacquired after a power reset. This means that the resolution of the
part can be compared easily to other methods that might otherwise require 12 or more bits of overall resolution.
The device operates on demand via a sync input pin. The sync input can also be used to avoid external noise sources and
cross-interference from adjacent QRG capacitive sensors. Unique among capacitance sensors, this device features
spread-spectrum burst modulation, permitting extremely high noise rejection characteristics for very robust signals even in
high EMI environments.
The device requires only a single sampling capacitor (Cs) to acquire signals. The value of this capacitor controls the gain of
the sensor, and it can be adjusted over 2錕?frac12; decades of range from 1nF to 500nF. No external switches, opamps, or other
components are required.
T
A
0 C to +70 C
-40
0
C to +85
0
C
0
0
AVAILABLE OPTIONS
SOIC
-
QT301-IS
8-PIN DIP
QT301-D
-
LQ
Copyright 漏 2003 QRG Ltd
QT301 R1.04 21/09/03
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