VRE125 データシートの表示（PDF） - Thaler Corporation
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VRE125 Datasheet PDF : 5 Pages
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DISCUSSION OF PERFORMANCE
THEORY OF OPERATION
APPLICATION INFORMATION
The following discussion refers to the schematic
below. A FET current source is used to bias a 6.3V
zener diode. The zener voltage is divided by the
resistor network R1 and R2. This voltage is then
applied to the noninverting input of the operational
amplifier which amplifies the voltage to produce a
5.000V output. The gain is determined by the
resistor networks R3 and R4: G=1 + R4/R3. The
6.3V zener diode is used because it is the most
stable diode over time and temperature.
The current source provides a closely regulated
zener current which determines the slope of the
reference's voltage vs. tamperature function. By
trimming the zener current a lower drift over
temperature can be achieved. But since the voltage
vs. temperature function is nonlinear, this method
leaves a residual error over wide temperature
ranges.
To remove this residual error, Thaler has
developed a nonlinear compensation network of
thermistors and resistors that is used in the VRE
series references. This proprietary network
eliminates most of the nonlinearity in the voltage vs.
temperature function. By then adjusting the slope,
Thaler Corporation produces a very stable voltage
over wide temperature ranges. This network is less
than 2% of the overall network resistance so it has
a negligible effect on long term stability.
Figure 1 shows the proper connection of the
VRE125 series voltage reference with the optional
trim resistors. When trimming the VRE127, the
positive voltage should be trimmed first since the
negative voltage tracks the positive side. Pay careful
attention to the circuit layout to avoid noise pickup
and voltage drops in the lines.
When using precision voltage references at high
temperatures it is best to keep them powered up. If
the zener diode isn't powered up at high
temperatures the junction will collect ions, and then
when power is applied, the voltage will drift until the
charge build up is depleted.
The VRE125 series voltage references have the
ground terminal brought out on two pins (pin 6 and
pin 7) which are connected together internally. This
allows the user to achieve greater accuracy when
using a socket. Voltage references have a voltage
drop across their power supply ground pin due to
quiescent current flowing through the contact
resistance. If the contact resistance was constant
with time and temperature, this voltage drop could be
trimmed out. When the reference is plugged into a
socket, this source of error can be as high as 20ppm.
By connecting pin 7 to the power supply ground and
pin 6 to a high impedance ground point in the
measurement circuit, the error due to the contact
resistance can be eliminated. If the unit is soldered
into place the contact resistance is sufficiently small
that it doesn't effect performance.
VRE125
VRE127
FIGURE 2
FIGURE 3
VRE125DS REV. C SEPT 1994
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