VRE117 데이터 시트보기 (PDF) - Thaler Corporation

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VRE117

Precision Reference Supplies

Thaler Corporation 

DISCUSSION OF PERFORMANCE

THEORY OF OPERATION

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

3.000V 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. 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 Corporation

has developed a nonlinear compensation network of

thermistors and resistors that is used in the VRE117

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 1 shows the proper connection of the

VRE117 series voltage reference with the optional

trim resistors. When trimming the VRE119, 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.

The VRE117 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.

VRE117

VRE119

VRE117DS REV. C NOV 2000

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