VRE410L Просмотр технического описания (PDF) - Thaler Corporation

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VRE410L

Precision Dual Reference

Thaler Corporation 

DISCUSSION OF PERFORMANCE

THEORY OF OPERATION

The following discussion refers to the schematic in

figure 2 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

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

compensation technique is not well suited for wide

temperature ranges.

Thaler Corporation has developed a nonlinear

compensation network of thermistors and resistors

that is used in the VRE series voltage references.

This proprietary network eliminates most of the

nonlinearity in the voltage vs. temperature function.

By 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.

The VRE405 reference has it’s ground terminal

brought out on two pins (pin 6 and 7) which are

connected 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.

VRE405

FIGURE 2

VRE405DS REV. A MAY 1996

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