CAV444 Datasheet, PDF (4/12 Pages) Analog Devices – C/V transmitter IC with adjustable output voltage for capacitive input signals

CAV444 – C/V transmitter IC
with adjustable output voltage
for capacitive input signals
PRINCIPLE OF MEASUREMENT
CAV444 is an integrated C/V (capacitance-to-voltage) converter circuit that contains full signal
conditioning and evaluation electronics for linear, capacitive signal sources.
The principle of measurement behind CAV444 is the conversion of a change in capacitance
(measurement capacitor, C_M) into a linear, differential output voltage. Measurement capacitor C_M
can be altered by the amount ∆C_M = C_M,_max – C_M,min (C_M,min is the basic capacitance of C_M).
HOW CAV444 WORKS
The CAV444 IC functions according to the following principle. The measurement capacitor is the
capacitor of an internal measurement oscillator. This generates the clock pulse with which the
measurement capacitor is charged and discharged. The number of clock pulses provided depends on
the measurement capacitor. These are converted into a DC voltage signal in the f/V converter and in
the backend lowpass filter. The filtered DC voltage signal travels to an adjustable amplifier stage
that enables the output signal to be set to the required value.
VTEMP
7
GND
10
RA ^{RA VCC VB}
14
11
3
Temperature-
Sensor
CAV444
Supply
VREF
6
CM
12
C_M
1
RCM
Measurement
oszillator
f/V
converter
16 2
CW RCW
Lowpass
filter
15 13
CF1 CF2
Output-
VOUT
stage ⁵
4
GAIN
Figure 2: Block diagram of CAV444 with signal patterns
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Phone: [phone]
Fax: [phone]
Internet: http://www.analogmicro.de
Email: [e-mail]
Mai 2010 - Rev 1.1 - Page 4/12