CAV424 Datasheet, PDF (9/16 Pages) List of Unclassifed Manufacturers – Converter IC for Capacitive Signals

CAV424 - C/U transducer IC
with adjustable output voltage
Figure 7 assumes that the charging currents I_CM and I_CR are constant. This means that with a change
in the basic value of the measurement capacitance C_M,min (as is the case when different objects are
measured, for example) the oscillator frequency must be adjusted to the new measurement with the
alternate C_M,min value.
If oscillator frequency f_osc is to be set as a parameter, when C_M,min is altered the two values I_CM and
I_CR must also be adjusted. It is recommended that I_CM = I_CR. Both procedures are equally effective;
the choice thereof depends on the conditions stipulated by the application.
A functional diagram is shown in Figure 8.
R R _CX
CM
R_OSC
7
CAV424
T Sensor
12
C_OSC
Reference
oscillator
16
C_R
14
C_M
Integrator 1
Integrator 2
10
R_CR
2
3
1
11
Current reference
6
Signal conditioning
5
15
13 4
V_CC
C_VM
V_M
V_DIFF
V_LPout
C_RL1
R R _L1
L2
C_{L 1}
C_L2
R_L3 R_A
R_B
GND
Figure 8: Functional diagram for CAV424 (with fosc constant)
If fosc = constant and I_CM, I_CR = f(C_M, C_R) the same equations (1 to 9) apply as for the case that I_CM
and I_CR = constant and fosc = f(C_M, C_R).
For dynamic measurements with periodically changeable measurement capacitances the various
frequencies must be taken into account. Among other things, the following applies:
f _det << f _osc
f_det is the detection frequency which gives the change in measurement capacity per unit of time.
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
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Internet:
http://www.analogmicro.de
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July 2007 - Rev 1.2 - Page 9/16