Editing Bandgap voltage reference

{{Short description|Reference voltage independent of temperature}}
A '''bandgap voltage reference''' is a [[voltage reference]] circuit widely used in [[integrated circuit]]s. It produces an almost constant [[voltage]] corresponding to the particular [[semiconductor]]'s theoretical [[band gap]], with very little fluctuations from variations of [[power supply]], [[electrical load]], time, [[temperature]] ({{As of|1999|lc=y}}, they typically have an initial error of 0.5–1.0% and a [[temperature coefficient]] of 25–50 [[Parts per million|ppm]]/[[°C]]).<ref>{{Cite web |last1=Miller |first1=Perry |last2=Moore |first2=Doug |date=November 1999 |title=Precision voltage references |url=http://www.ti.com/lit/an/slyt183/slyt183.pdf |url-status=live |archive-url=https://web.archive.org/web/20230517113214/http://www.ti.com/lit/an/slyt183/slyt183.pdf |archive-date=2023-05-17 |access-date=2024-01-20 |website=[[Texas Instruments]]}}</ref>

David Hilbiber of [[Fairchild Semiconductor]] filed a [[patent]] in 1963<ref>{{Cite patent|number=US3271660A|title=Reference voltage source|gdate=1966-09-06|invent1=Hilbiber|inventor1-first=David F.|url=https://patents.google.com/patent/US3271660A/en}}</ref> and published this circuit concept in 1964.<ref name="Hilbiber1964">
{{Cite conference
  | first = D.F. |last=Hilbiber
  |title=1964 IEEE International Solid-State Circuits Conference. Digest of Technical Papers
 | chapter = A new semiconductor voltage standard
  | conference = 1964 International Solid-State Circuits Conference: Digest of Technical Papers
  | volume = 2
  | pages = 32–33
  | year = 1964
  | doi=10.1109/ISSCC.1964.1157541
}}</ref> [[Bob Widlar]],<ref name="Widlar1971">
{{Citation
  | doi = 10.1109/JSSC.1971.1050151
  | bibcode = 1971IJSSC...6....2W
 | last = Widlar
  | first = Robert J.
  | s2cid = 14461709
 | authorlink = Bob Widlar
  | title = New Developments in IC Voltage Regulators
  | journal = IEEE Journal of Solid-State Circuits
  | volume = 6
  | issue = 1
  | pages = 2–7
  | date = February 1971
}}</ref> [[Paul Brokaw]]<ref name="Brokaw1974">
{{Citation
  | doi = 10.1109/JSSC.1974.1050532
  | bibcode = 1974IJSSC...9..388B
 | last = Brokaw
  | first = Paul
  | s2cid = 12673906
 | authorlink = Paul Brokaw
  | title = A simple three-terminal IC bandgap reference
  | journal = IEEE Journal of Solid-State Circuits
  | volume = 9
  | issue = 6
  | pages = 388–393
  | date = December 1974
}}</ref> and others<ref name="BanbaEtAl1999">
{{Citation
  | doi = 10.1109/4.760378
  | bibcode = 1999IJSSC..34..670B
 | last1 = Banba
  | first1 = H.
  | last2 = Shiga
  | first2 = H.
  | last3 = Umezawa
  | first3 = A.
  | last4 = Miyaba
  | first4 = T.
  | last5 = Tanzawa
  | first5 = T.
  | last6 = Atsumi
  | first6 = S.
  | last7 = Sakui
  | first7 = K.
  | s2cid = 10495180
 | title = A CMOS bandgap reference circuit with sub-1-V operation
  | journal = IEEE Journal of Solid-State Circuits
  | volume = 34
  | issue = 5
  | pages = 670–674
  | date = May 1999
}}</ref> followed up with other commercially-successful versions.

==Operation==
[[Image:Bandgap-reference.svg|thumb|Circuit of a [[Brokaw bandgap reference]]]]
[[Image:Bandgap-charakteristic.svg|thumb|Characteristic and balance point of T1 and T2]]
The voltage difference between two [[p–n junction]]s (e.g. [[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 −2{{nbsp}}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.

Although [[silicon]]'s (Si) [[band gap]] at [[absolute zero|0{{nbsp}}K]] is technically 1.165{{nbsp}}[[Electronvolt|eV]], the circuit essentially linearly extrapolates the bandgap–temperature curve<ref>https://people.engr.tamu.edu/s-sanchez/607%20Lect%204%20Bandgap-2009.pdf slides 8-9 and https://users.wpi.edu/~mcneill/handouts/BandgapPrinciple.pdf graph this linear extrapolation</ref> to determine a slightly higher but precise reference around 1.2–1.3{{nbsp}}V (the specific value depends on the particular technology and circuit design); 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 [[parabola|parabolic]] residual behavior since the linear (first order) effects are chosen to cancel.

Because the output voltage is by definition fixed around 1.25{{nbsp}}V for typical Si bandgap reference circuits, the minimum operating voltage is about 1.4{{nbsp}}V, as in a [[CMOS]] circuit at least one drain-source voltage of a [[field-effect transistor]] (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.<ref name="BanbaEtAl1999" />

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 20{{nbsp}}ppm/°C, over a temperature range of 100{{nbsp}}°C. For this reason, in 2001, Malcovati<ref>{{Cite journal | doi=10.1109/4.933463 |bibcode = 2001IJSSC..36.1076M|title = Curvature-compensated BiCMOS bandgap with 1-V supply voltage|year = 2001|last1 = Malcovati|first1 = P.|last2 = Maloberti|first2 = F.|last3 = Fiocchi|first3 = C.|last4 = Pruzzi|first4 = M.|journal = IEEE Journal of Solid-State Circuits|volume = 36|issue = 7|pages = 1076–1081|s2cid = 7504312|citeseerx = 10.1.1.716.6243}}</ref> 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 <ref name="BanbaEtAl1999" /> topology and an analysis of base-emitter temperature effects that was performed by Tsividis in 1980.<ref>Y. P. Tsividis, "Accurate analysis of temperature effects in Ic-Vbe characteristics with application to bandgap reference sources," IEEE J. Solid-State Circuits, vol. 15, no. 6, pp. 1076 – 1084, Dec. 1980.</ref> In 2012, Andreou<ref>{{cite journal|doi=10.1109/JSSC.2011.2173267|title=A Novel Wide-Temperature-Range, 3.9 PPM/°C CMOS Bandgap Reference Circuit|year=2012|last1=Andreou|first1=Charalambos M.|last2=Koudounas|first2=Savvas|last3=Georgiou|first3=Julius|journal=IEEE Journal of Solid-State Circuits|volume=47|issue=2|pages=574–581|bibcode=2012IJSSC..47..574A |s2cid=34901947}}</ref><ref>{{cite book|doi=10.1109/ISCAS.2010.5537621|isbn=978-1-4244-5308-5|chapter=A novel CMOS Bandgap reference circuit with improved high-order temperature compensation|title=Proceedings of 2010 IEEE International Symposium on Circuits and Systems|year=2010|last1=Koudounas|first1=Savvas|last2=Andreou|first2=Charalambos M.|last3=Georgiou|first3=Julius|pages=4073–4076|s2cid=30644500}}</ref> 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]] and lower [[noise (electronics)|noise]].

The other critical issue in design of bandgap references is power efficiency and size of circuit. As a bandgap reference is generally based on [[Bipolar junction transistor|BJT]] 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.<ref>{{cite book|doi=10.1109/ISCAS.2004.1328127|isbn=0-7803-8251-X|chapter=Design and optimization of a high PSRR CMOS bandgap voltage reference|title=2004 IEEE International Symposium on Circuits and Systems (IEEE Cat. No.04CH37512)|year=2004|last1=Tajalli|first1=A.|last2=Atarodi|first2=M.|last3=Khodaverdi|first3=A.|last4=Sahandi Esfanjani|first4=F.|pages=I-45-I-48|s2cid=9650641}}</ref>

Despite these limitations, the band gap voltage reference is widely used in voltage regulators, covering the majority of 78xx, 79xx devices along with the [[TL431]] and the complementary [[LM317]] and LM337. Temperature coefficients as low as 1.5–2.0{{nbsp}}ppm/°C can be obtained with bandgap references.{{efn|For example, LT6657 from Linear Technology and ADR4550 from Analog Devices.}} However, the parabolic characteristic of voltage versus temperature means that a single figure in ppm/°C does not adequately describe the behavior 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. Bandgap references are also suited for low-power applications.{{efn|For example, 1{{nbsp}}μA cathode current with the Maxim Integrated MAX6009 shunt voltage reference.}}

[[Mixed-signal integrated circuit|Mixed-signal]] [[microcontrollers]] may provide an internal bandgap reference signal to be used as reference for any internal [[comparator]](s) and [[analog-to-digital converter]](s).

==Patents==
* 1966, US Patent 3271660, ''Reference voltage source'', David Hilbiber.<ref>[https://patents.google.com/patent/US3271660 US Patent 3271660 - ''Reference voltage source'', David F Hilbiber; United States Patent and Trademark Office; September 6, 1966.]</ref>
* 1971, US Patent 3617859, ''Electrical regulator apparatus including a zero temperature coefficient voltage reference circuit'', [[Robert Dobkin]] and [[Bob Widlar|Robert Widlar]].<ref>[https://patents.google.com/patent/US3617859 US Patent 3617859 - ''Electrical regulator apparatus including a zero temperature coefficient voltage reference circuit''; Robert C Dobkin and Robert J Widlar; United States Patent and Trademark Office; November 2, 1971.]</ref>
* 1981, US Patent 4249122, ''Temperature compensated bandgap IC voltage references'', [[Bob Widlar|Robert Widlar]].<ref>[https://patents.google.com/patent/US4249122 US Patent 4249122 - ''Temperature compensated bandgap IC voltage references''; Robert J Widlar; United States Patent and Trademark Office; February 3, 1981.]</ref>
* 1984, US Patent 4447784, ''Temperature compensated bandgap voltage reference circuit'', [[Robert Dobkin]].<ref>[https://patents.google.com/patent/US4447784 US Patent 4447784 - ''Temperature compensated bandgap voltage reference circuit''; Robert C Dobkin; United States Patent and Trademark Office; May 8, 1984.]</ref>

==Notes==
{{noteslist}}

==See also==
* [[Brokaw bandgap reference]]
* [[LM317]]
* [[TL431]]
* [[Silicon bandgap temperature sensor]]

==References==
{{Reflist|2}}

==External links==
* [https://web.archive.org/web/20160303220955/http://www.ti.com/ww/en/bobpease/assets/www-national-com_rap.pdf The Design of Band-Gap Reference Circuits: Trials and Tribulations]&nbsp;p.&nbsp;286 &ndash; Robert Pease, National Semiconductor
* [http://ecad.tu-sofia.bg/et/1999/Statii%20ET99-I/Features%20and%20Limitations%20of%20CMOS%20Voltage%20References.pdf Features and Limitations of CMOS Voltage References]
* [http://www.tedpavlic.com/teaching/osu/ece327/lab3_vreg/lab3_vreg_lm317_example.pdf ECE 327: LM317 Bandgap Voltage Reference Example]&nbsp;&ndash; Brief explanation of the temperature-independent bandgap reference circuit within the LM317.

{{DEFAULTSORT:Bandgap Voltage Reference}}
[[Category:Electronic circuits]]
[[Category:Analog circuits]]