|
Temperature Correction for Attenuator Digital
Driver Unit
During this R&D project, an AD7816 temperature sensor chip was
used for temperature correction for
Digital
Driver Unit for Voltage-Controlled Variable Attenuator of VCVA
series. The AD7816 temperature sensor is a commercially
available chip which allows obtaining an ambient temperature
via serial interface. AD7816 was installed on VCVA chassis and
connected to PROM memory (photo on fig.1). For transmitting
AD7816 signals into the attenuator driver unit we replaced
standard DB9 output connector to enhanced DB19 connector and
made a special cable with an extender for RS-232 interface.
 |
|
Fig.1. Photo of Digital
Driver Unit with AD7816 temperature sensor chip |
Calibration procedure was as the following:
1. We obtained nonlinear dependencies attenuation vs input code
and temperature. These dependencies are shown on fig 2.
 |
|
Fig.2. Dependencies of attenuation vs input code and
temperature |
2. Achieved data was recalculated for obtaining a linear
dependence attenuation vs input code. Suchwise we have 7
corrected dependencies for different temperature: +10C,
+15C…+40C (fig.3).
 |
|
Fig.3. Corrected curves for temperature range from +10C to
+40C |
3. We rewrote software inside the PROM, so it can read
temperature from AD7816 chip and correct VCVA output code
according to obtained temperature. Software uses linear
approximation between 7 calibration tables for different
temperatures. The final temperature test for VCVA Ser.Num.0076
is presented on fig.4. These curves show the difference between
an ideal linear attenuation (Code*0.125dB) and real attenuation
level in dB.
 |
|
Fig.4. Attenuation numbers with temperature correction for
VCVA Ser.Num.0076 |
Since Feb 2003, Digital Driver Unit
for Solid State Voltage Controlled Attenuators of VCVA series
can be shipped with temperature correction as an option.
|
