A bandgap voltage reference is a voltage reference circuit widely used in integrated circuits, usually with an output voltage around 1.25 V, close to the theoretical bandgap of silicon at 0 K. Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance as coarse powder, dark grey with bluish tinge Standard atomic weight 28. ...

The operation principle of bandgap voltage references is quite straightforward. The voltage difference between two diodes, often operated at the same current and of different junction areas, is used to generate a proportional to absolute temperature (PTAT) current in a first resistor. This current is used to generate a voltage in a second resistor. This voltage in turn is added to the voltage of one of the diodes (or a third one, in some implementations). The voltage across a diode operated at constant current, or here with a PTAT current, is complementary to absolute temperature (CTAT—reduces with increasing temperature), with approximately −2 mV/K. If the ratio between the first and second resistor is chosen properly, the first order effects of the temperature dependency of the diode and the PTAT current will cancel out. The resulting voltage is about 1.2–1.3 V, depending on the particular technology, and is close to the theoretical bandgap of silicon at 0 K. The remaining voltage change over the operating temperature of typical integrated circuits is on the order of a few millivolts. This temperature dependency has a typical parabolic behavior. Types of diodes. ... In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. ...

Since the output voltage is by definition fixed around 1.25 V for typical bandgap reference circuits, the minimum operating voltage is about 1.4 V, as in a CMOS circuit at least one drain-source voltage of a FET (field effect transistor) has to be added. Therefore, recent work concentrates on finding alternative solutions, in which for example currents are summed instead of voltages, resulting in a lower theoretical limit for the operating voltage (Banba, 1999). Static CMOS Inverter Complementary metal–oxide–semiconductor (CMOS) (see-moss, IPA: ), is a major class of integrated circuits. ... Large power N-channel field effect transistor The field-effect transistor (FET) is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel in a semiconductor material. ...

Note that sometimes confusion arises when using the abbreviation CTAT, where the "C" is incorrectly taken to mean "constant" rather than "complementary". To avoid this confusion, although not in widespread use, the term constant with temperature (CWT) is sometimes used. CWT is a three-letter abbreviation with multiple meanings, including: Continuous wavelet transform cwt – hundred weight – weight equal to 100 pounds. ...

References

• Brokaw, P., "A simple three-terminal IC bandgap reference", 'IEEE Journal of Solid-State Circuits', vol. 9, pp. 388 - 393, December 1974.
• Widlar, R., "New Developments in IC Voltage Regulators", 'IEEE Journal of Solid-State Circuits', vol. 6, pp. 2 - 7, February 1971.
• Banba, H., Shiga, H., Umezawa, A., Miyaba, T., Tanzawa, T., Atsumi, S., Sakui, K., "A CMOS bandgap reference circuit with sub-1-V operation", 'IEEE Journal of Solid-State Circuits', vol. 34, pp. 670 - 674, May 1999.