VRE104
Precision
Reference Supplies
THALER CORPORATION • 2015 N. FORBES BOULEVARD • TUCSON, AZ. 85745 • (520) 882-4000
FEATURES
•
VERY HIGH ACCURACY: 4.5000 V OUTPUT ±0.4 mV
•
EXTREMELY LOW DRIFT: 0.6 ppm/°C -55°C to +125°C
•
EXCELLENT STABILITY: 6 ppm/1000 Hrs. Typ.
•
EXCELLENT LINE REGULATION: 6 ppm/V Typ.
•
WIDE SUPPLY RANGE: +13.5 to +22.0 V
•
HERMETIC 14-PIN CERAMIC DIP
•
MILITARY PROCESSING OPTIONS
APPLICATIONS
•
PRECISION A/D and D/A CONVERTERS
•
TRANSDUCER EXCITATION
•
ACCURATE COMPARATOR THRESHOLD
REFERENCE
•
HIGH RESOLUTION SERVO SYSTEMS
•
DIGITAL VOLTMETERS
•
HIGH PRECISION TEST and
MEASUREMENT INSTRUMENTS
DESCRIPTION
VRE104 Series Precision Voltage References
provide ultrastable +4.500 V outputs with up to
±0.4 mV initial accuracy and temperature
coefficient as low as 0.6 ppm/°C over the full
military temperature range.
These references are specifically designed to be
used with the Crystal Semiconductor line of
successive-approximation type Analog to Digital
Converters (ADCs). This line of ADCs sets new
standards for temperature drift, which can only be
as good as the external reference used. The
Thaler VRE104 combined with a Crystal ADC will
provide the lowest drift data conversion
obtainable.
SELECTION GUIDE
Type
VRE104C
VRE104CA
VRE104M
VRE104MA
Output
+4.5V
+4.5V
+4.5V
+4.5V
Temperature
Max. Volt
Operating Range Deviation
-25°C to +85°C
-25°C to +85°C
-55°C to +125°C
-55°C to +125°C
0.4mV
0.2mV
0.6mV
0.3mV
VRE104 series devices are available in two operating temperature ranges, -25°C to +85°C and -55°C to
+125°C, and two performance grades. All devices are packaged in 14-pin hermetic ceramic packages for
maximum long-term stability. "M" versions are screened for high reliability and quality.
Superior stability, accuracy, and quality make the VRE104 ideal for all precision applications which may
require a 4.5V reference. High-accuracy test and measurement instrumentation, and transducer excitation are
some other applications which can benefit from the high accuracy of the VRE104.
VRE104DS REV. C SEPT 1994
DISCUSSION OF PERFORMANCE
THEORY OF OPERATION
The following discussion refers to the schematic
below. A FET current source is used to bias a 6.3
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
4.5000V output. The gain is determined by the
resistor networks R3 and R4: G=1 + R4/R3. The 6.3
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
references' voltage vs. temperature 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 VRE104
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.
APPLICATION INFORMATION
Figure 2 shows the proper connection of the
VRE104 series voltage references with the optional
trim resistors. Pay careful attention to the circuit
layout to avoid noise pickup and voltage drops in the
lines.
The VRE104 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 does not effect performance.
VRE104
FIGURE 1
VRE104DS REV. C SEPT 1994
Microcontroller MCU
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