CAV424 Datasheet, PDF (4/16 Pages) List of Unclassifed Manufacturers – Converter IC for Capacitive Signals

CAV424 - C/U transducer IC
with adjustable output voltage
PRINCIPLE OF MEASUREMENT
CAV424 is an integrated C/U converter circuit which contains full signal conditioning electronics
for capacitive signal sources.
I_M I_R
C_M C_R
V_CC
CAV424 _UOUT
Current sources I_M and I_R are integrated in CAV424
Figure 2: Principle of capacitance measurement using CAV424
The principle of measurement with the CAV424 entails recording a change in capacitance in a
sensor bridge comprising two adjustable current sources and two capacitors, the measurement
capacitance (C_M) of which can be altered by the amount !C_M = C_M,_max– C_M,min. The second
capacitor is defined as a reference (C_R, see Figure 2). C_M,min is the basic capacitance of C_M. The
change in measurement capacitance is compared to the fixed reference capacitance C_R and the
resulting signal converted into an output voltage signal.
HOW CAV424 WORKS
The CAV424 IC functions according to the following principle. An adjustable oscillator, the
frequency of which is set using capacitor C_OSC, drives two symmetrical integrators which are phase-
locked and clock-synchronized (see Figure 3). The amplitudes of the two driven integrators are
determined by capacitors C_R and C_M. With high common-mode rejection and a high resolution, the
difference between the two amplitudes produces a signal which corresponds to the difference in
capacitance between C_R and C_M (rectifier effect). This difference signal is then filtered in an
ensuing active low pass. The resulting voltage signal passes on to an adjustable amplifier stage
which sets the output signal to the required value.
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Phone: [phone]
Fax: [phone]
Internet:
http://www.analogmicro.de
Email: [e-mail]
July 2007 - Rev 1.2 - Page 4/16