A precision reference voltage source

With increasing temperature the base-emitter voltage of a transistor with a constant current decreases, while the difference in base-emitter voltages of two identical (integrated) transistors having a constant current ratio increases. From the sum of the two voltages a nearly temperature- independent output voltage is obtained if this sum equals the gap voltage of silicon. A reference voltage source of 10 V based on the principle is described. The reference part of the circuit is an integrated circuit, and thin-film resistors with a small relative temperature coefficient are used. An operational amplifier and a few resistors and capacitors complete the circuit. The source has a parabolic temperature characteristic and the temperature peak can be controlled by resistor adjustment. A change of /spl plusmn/10 K in respect of the peak temperature causes an output voltage change of -250 /spl mu/V, while a change of /spl plusmn/30 K causes a change of -2.2 mV. A long-term stability of 10 ppm/month was measured. The circuit can compete with the best available Zener diode sources, and has the added advantage that practically no selection is necessary.