CAV444 Datasheet, PDF (8/12 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
OUTPUT VOLTAGES
The following applies to the output voltage: V_OUT = V_DIFF + V_REF
V_OUT (Volt)
5
4
V _{OUT , max}
2,5
1
V _{OUT , min}
0
+V_{DI FF}
-V_{D IFF}
V_CC
V_REF
Figure 6: Maximum output voltage VOUT
THE DIMENSIONING PROCESS
Excel program Kali_CAV444.xls should be used for dimensioning purposes.
The dimensioning process for CAV444 assumes that in addition to measurement capacitor C_M and
the f/V converter capacitor C_W, parasitic capacitances in both the IC and measurement circuit also
influence the signal pattern.
For this reason the offset and full scale are calibrated based on the installed system, where all
parasitic capacitances and exemplary variations in the components used have been taken into
account.
Taking transfer function (6) as its basis, the Excel spreadsheet Kali_CAV444.xls [1] first computes
suitable values for a measurement operating point. The circuit output is measured at this point and
these measurements then entered into the program in stage two of the procedure. The algorithm
calculates the two adjusting resistors required to calibrate the system. Once these have been placed
in the circuit, the calibration of both offset and span is complete.
INITIAL OPERATION
Initial operation is described in detail in the description of the calibration program (see
Kali_CAV444.xls).
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 8/12