Features

Very high accuracy: +4.5 V output, ±0.8 mV Very low drift: 1.48 ppm/°C (-55°C to +125 °C) Excellent stability: 6 ppm/1000 hours. Typical Excellent Line Regulation: 6 ppm/v Typical Wide Supply Range: +13.5 to +22.0 V Sealed 14-Pin Ceramic Immersion Reference Resolution Servo System Word Voltmeter Accuracy ISION Test and Measurement Instruments

Description: The VRE104 series of precision voltage references provide an ultra-stable +4.5 V output with an initial accuracy of up to ±0.8 mV and a temperature coefficient as low as 1.48 ppm/°C over the full military temperature range. These references are specifically designed for use with crystalline semiconductor lines of continuous approximation analog-to-digital converters (ADCs). This range of automatic temperature control systems sets new standards for temperature drift and can only be used as an external reference. The VRe104 combined with the ADC will provide the lowest drift data conversion achievable. The 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 hermetically sealed ceramic for maximum long-term stability. The "M" version is screened for high reliability and quality. Excellent stability, accuracy and quality make the VRe104 ideal for all precision applications that may require a 4.5 V reference voltage. High-precision test and measurement instruments, and sensor excitation are some other applications that can benefit from the high accuracy of the VRE104.

Principle of Operation The following discussion refers to the block diagram in FIG. 1 . A FET current source is used to bias the 6.3V Zener diode. The zener voltage is divided by the resistor network R1 and R2. This voltage is then applied to the non-inverted input of the op amp, which amplifies the voltage, producing a 4.5 V output. The gain is determined by the resistor network r3 and r4: g=1+r4/r3. The 6.3V Zener is used because it is the most stable diode over time and temperature. The current source provides a tightly regulated zener current that determines the slope of the reference voltage as a function of temperature. By fine-tuning the zener current, lower temperature drift can be achieved. But because the voltage-temperature function is nonlinear, the method has residual error in a wide temperature range. To eliminate this residual error, a nonlinear compensation network for thermistors and resistors of the VRE104 series reference was developed. This specialized network removes most of the nonlinearity of the voltage-temperature function. By adjusting the slope, the VRE104 series produces a very stable voltage over a wide temperature range. This network is less than 2% of the total network resistance and therefore has a negligible effect on long-term stability.

Application Information The correct connections for the VRE104 series reference voltage are shown below, with optional trimmer resistors. Pay attention to the circuit layout to avoid noise and voltage drops in the lines. The ground terminal of the VRE104 series voltage reference is brought out from two pins that are connected together internally (pin 6 and pin 7). This allows the user to get more precision when working with sockets. The voltage reference has a voltage drop across its power supply ground due to quiescent current flowing through the contact resistance. This voltage drop can be eliminated if the contact resistance varies with time and temperature. This source of error can be as high as 20ppm when the reference is plugged into the socket. Errors due to contact resistance can be eliminated by connecting pin 7 to power ground and pin 6 to a high impedance ground point in the measurement circuit. If the unit is soldered in place, the contact resistance is small enough not to affect performance. VRe104 for crystalline semiconductor ADC