VRE100CA Просмотр технического описания (PDF) - Thaler Corporation

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VRE100CA

Precision Reference Supplies

Thaler Corporation 

DISCUSSION OF PERFORMANCE

THEORY OF OPERATION

The following discussion refers to the schematic

below. In operation, approximately 6.3 volts is

applied to the noninverting input of the op amp. The

voltage is amplified by the op amp to produce a

10.000V output. The gain is determined by the

networks R1 and R2: G=1 + R2/R1. The 6.3V zener

diode is used because it is the most stable diode

over time and temperature.

The zener operating current is derived from the

regulated output voltage through R3. This feedback

arrangement provides a closely regulated zener

current. This current 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 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. By using highly stable

resistors in our network, we produce a voltage

reference that also has very good long term stability.

APPLICATION INFORMATION

Figure 1 shows the proper connection of the

VRE100 series voltage reference with the optional

trim resistors. When trimming the VRE102, 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 VRE100 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. The VRE series

voltage references can be connected with or without

the use of pin 6 and still provide performance

superior to the 2700 and 2710 series voltage

references.

VRE100

VRE102

4-23

VRE100DS REV. D MAY 1995

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