A bandgap voltage reference is a temperature independent
voltage reference circuit widely used in
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
s. It produces a fixed (constant)
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
regardless of power supply variations, temperature changes, or circuit loading from a device. It commonly has an output voltage around 1.25V (close to the theoretical
band gap of
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
at
0K). This circuit concept was first published by David Hilbiber in 1964.
[
] Bob Widlar,
[
] Paul Brokaw Paul Brokaw is an expert on integrated circuit design who has spent most of his career at Analog Devices, where he holds the position of Analog Fellow. He is the inventor of many analog IC circuits, including the Brokaw bandgap reference and holds o ...
[
] and others
[
] followed up with other commercially successful versions.
Operation
The voltage difference between two
p–n junction
A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contains ...
s (e.g.
diode
A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.
A diode ...
s), operated at different current densities, is used to generate a current that is ''proportional to absolute temperature'' (''PTAT'') in a 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 junctions (or a third one, in some implementations). The voltage across a diode operated at constant current is ''complementary to absolute temperature'' (''CTAT''), with a temperature coefficient of approximately −2mV/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 1.2–1.3V, depending on the particular technology and circuit design, and is close to the theoretical 1.22eV
bandgap of
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
at
0K. The remaining voltage change over the
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
of typical integrated circuits is on the order of a few millivolts. This temperature dependency has a typical
parabolic residual behavior since the linear (first order) effects are chosen to cancel.
Because the output voltage is by definition fixed around 1.25V for typical bandgap reference circuits, the minimum operating voltage is about 1.4V, as in a
CMOS
Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...
circuit at least one drain-source voltage of a
field-effect transistor
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contro ...
(FET) 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.
The first letter of the acronym, CTAT, is sometimes misconstrued to represent ''constant'' rather than ''complementary''. The term, ''constant with temperature'' (''CWT''), exists to address this confusion, but is not in widespread use.
When summing a PTAT and a CTAT current, only the linear terms of current are compensated, while the higher-order terms are limiting the temperature drift (TD) of the bandgap reference at around 20ppm/°C, over a temperature range of 100°C. For this reason, in 2001, Malcovati designed a circuit topology that can compensate high-order non-linearities, thus achieving an improved TD. This design used an improved version of Banba's
topology and an analysis of base-emitter temperature effects that was performed by Tsividis in 1980. In 2012, Andreou has further improved the high-order non-linear compensation by using a second
operational amplifier along with an additional resistor leg at the point where the two currents are summed up. This method enhanced further the curvature correction and achieved superior TD performance over a wider temperature range. In addition it achieved improved
line regulation Line regulation is the ability of a power supply to maintain a constant output voltage despite changes to the input voltage, with the output current drawn from the power supply remaining constant.
:\text = \frac \cdot 100\%
where ΔVi is the chang ...
and lower
noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
.
The other critical issue in design of bandgap references is power efficiency and size of circuit. As a bandgap reference is generally based on
BJT
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar t ...
devices and resistors, the total size of circuit could be large and therefore expensive for IC design. Moreover, this type of circuit might consume a lot of power to reach to the desired noise and precision specification.
Despite these limitations, the bandgap voltage reference is widely used in voltage regulators, covering the majority of 78xx, 79xx devices along with the LM317, LM337 and
TL431
The TL431 is a three-terminal adjustable precision shunt voltage regulator integrated circuit. With the use of an external voltage divider, a TL431 can regulate voltages ranging from 2.5 to 36 V, at currents up 100 mA. The typical initial deviati ...
devices. Temperature coefficients as low as 1.5–2.0ppm/°C can be obtained with bandgap references. However, the parabolic characteristic of voltage versus temperature means that a single figure in ppm/°C does not adequately describe the behaviour of the circuit. Manufacturers' data sheets show that the temperature at which the peak (or trough) of the voltage curve occurs is subject to normal sample variations in production. Bandgaps are also suited for low-power applications.
Patents
* 1966, US Patent 3271660, ''Reference voltage source'', David Hilbiber.
* 1971, US Patent 3617859, ''Electrical regulator apparatus including a zero temperature coefficient voltage reference circuit'',
Robert Dobkin
Robert C. Dobkin (born 1943 in Philadelphia) is an American electrical engineer, co-founder of Linear Technology Corporation, and veteran linear (analog) integrated circuit (IC) designer.
Career
Dobkin studied Electrical Engineering at MIT, ...
and
Robert Widlar.
* 1981, US Patent 4249122, ''Temperature compensated bandgap IC voltage references'',
Robert Widlar.
* 1984, US Patent 4447784, ''Temperature compensated bandgap voltage reference circuit'',
Robert Dobkin
Robert C. Dobkin (born 1943 in Philadelphia) is an American electrical engineer, co-founder of Linear Technology Corporation, and veteran linear (analog) integrated circuit (IC) designer.
Career
Dobkin studied Electrical Engineering at MIT, ...
.
US Patent 4447784 - ''Temperature compensated bandgap voltage reference circuit''; Robert C Dobkin; United States Patent and Trademark Office; May 8, 1984.
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Notes
See also
* Brokaw bandgap reference Brokaw bandgap reference is a voltage reference circuit widely used in integrated circuits, with an output voltage around 1.25 V with low temperature dependence. This particular circuit is one type of a bandgap voltage reference, named after Paul Br ...
* LM317
* Silicon bandgap temperature sensor The silicon bandgap temperature sensor is an extremely common form of temperature sensor (thermometer) used in electronic equipment. Its main advantage is that it can be included in a silicon integrated circuit at very low cost. The principle of t ...
References
External links
The Design of Band-Gap Reference Circuits: Trials and Tribulations
nbsp;p. 286 – Robert Pease, National Semiconductor
Features and Limitations of CMOS Voltage References
ECE 327: LM317 Bandgap Voltage Reference Example
nbsp;– Brief explanation of the temperature-independent bandgap reference circuit within the LM317.
{{DEFAULTSORT:Bandgap Voltage Reference
Electronic circuits
Analog circuits