EP2329230A1 - Circuit sensible à la température - Google Patents

Circuit sensible à la température

Info

Publication number
EP2329230A1
EP2329230A1 EP08788717A EP08788717A EP2329230A1 EP 2329230 A1 EP2329230 A1 EP 2329230A1 EP 08788717 A EP08788717 A EP 08788717A EP 08788717 A EP08788717 A EP 08788717A EP 2329230 A1 EP2329230 A1 EP 2329230A1
Authority
EP
European Patent Office
Prior art keywords
transistor
branch
circuit
transistors
current
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08788717A
Other languages
German (de)
English (en)
Inventor
George Hedley Storm Rokos
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Adaptalog Ltd
Original Assignee
Adaptalog Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Adaptalog Ltd filed Critical Adaptalog Ltd
Publication of EP2329230A1 publication Critical patent/EP2329230A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
    • G05F3/02—Regulating voltage or current
    • G05F3/08—Regulating voltage or current wherein the variable is dc
    • G05F3/10—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics
    • G05F3/16—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices
    • G05F3/20—Regulating voltage or current wherein the variable is dc using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations
    • G05F3/30—Regulators using the difference between the base-emitter voltages of two bipolar transistors operating at different current densities

Definitions

  • the present invention relates to a temperature sensor, in particular to a temperature sensor that develops a current that is proportional to absolute temperature.
  • the invention equally relates to the provision of a bandgap Voltage reference circuit (see for example US 4,447,784, US 3, 617, 859) .
  • Widlar and Dobkin arranged the circuit so that the control current is generated in Transistor QW, by directly connecting the bases of the transistors QD and QW, and placing a resistor RW between the emitters of QD and QW such that the PTAT Voltage is generated across RW.
  • RW is generally manufactured in an integrated circuit technology, its value is generally not independent of temperature, and the current generated will not be strictly proportional to absolute temperature; however, in accordance with accepted practice, both the Voltage and the current will be described as PTAT in the remainder of this document.
  • Figure Ib shows the PTAT cell in association with its feedback circuit.
  • the basic current mirror of figure Ia combined with circuitry to maintain the currents. This also is based on US 3,617,859.
  • the arrangement is designed for use in a bandgap regulator, with output Vreg of about 1.2-Volts.
  • the ratio of the resistor values Rsnsl:Rsns2 sets the ratio of the currents I (QW) : I (QD), and thus the Voltage across RW.
  • the current through Rsns2 is substantially the current in RW, so the voltage across RW together with the ratio Rsns2:RW sets the PTAT Voltage that is added to the base-emitter Voltage of Qctrl to generate the output Voltage.
  • the collector current of the Transistor QW is not exactly equal to the emitter current that is generated in RW.
  • This error is due to the finite current gain (known as the beta of the Transistor, "Beta") that requires current to flow into the base of the Transistor in order to maintain the collector current.
  • This error may be compensated by the base current of Qctrl, which is set by the current in Rsns3 and the Beta of Qctrl. In this way, the error due to finite Beta can be corrected, limited primarily by the matching of the Beta between the different transistors. Although this arrangement can work well from the aspect of accuracy, it requires significant additional current to effect the Beta compensation.
  • the arrangement also has PTAT characteristics when combined with circuitry that maintains the current ratio I (QF) : I (QD) .
  • I (QF) current ratio
  • I (QD) current ratio
  • One useful feature of this arrangement is that, in contrast to the arrangement of Widlar and Dobkin, the output current can be made to increase as Beta reduces (and the base current increases) . Accordingly, it was not long before a combined arrangement appeared in a bandgap reference circuit - the LMl 13 shown in simplified form in figure 4.
  • the resistor RF serves to simplify the stabilisation of the part against oscillation by providing a constant bias to the base of QW; it also provides a measure of compensation for the finite Beta, but this is clearly insufficient, as evidenced by the use of the resistor RC.
  • the Transistor polarity refers to the relative potentials of the emitter and collector terminals.
  • PNP Transistor When the voltage in operation is higher at the Emitter is higher than at the collector, it is referred to as a PNP Transistor, when the Emitter potential is lower than the Collector potential in operation, it is referred to as an NPN
  • PNP and NPN Transistors are referred to as having opposite polarity or being complementary.
  • the techniques described herein are most widely understood when used with devices where the current under identical bias voltage conditions depends substantially linearly on a physical area. This is typically the case for traditional vertical bipolar transistors, where the relevant area is the physical area of the emitter junction.
  • the equivalent parameter for FETs would be the quotient width/length, where the width of the FET is the effective gate dimension in the direction perpendicular to the current flow, and the length is the effective gate dimension along the direction of current flow.
  • the same criterion would apply to lateral bipolar transistors where the physical depth of the active base region is independent of the lateral dimensions, as is broadly the case for many lateral PNP transistors whose base is defined by a MOSFET gate.
  • resistor is to describe a circuit element or elements that provide the described function. It may be an individual resistor structure, or part or all of a network. Specifically, a number of resistors of equivalent function may be merged into a single structure, so a defined Resistor may not provide external terminals at that correspond to the defined potentials. This is specifically the case for the some of the Resistors equivalent to RW of figure Ia, when PTAT circuits using complementary Transistors are arranged with the emitters of the reference transistors adjacent or separated only by resistors.
  • a Branch of a PTAT circuit is defined as a section of the circuit whose currents are provided substantially from a set of Collectors, and includes all Transistors whose
  • Collectors provide current into that Branch, as well as the resistors through which the currents in those Transistors flow.
  • a "Regulating" Resistor is a Resistor through which current in one of the PTAT branches creates a potential difference whose value directly “Regulates” the potentials on the Control terminal of a Transistor.
  • the resistors RF and RW are Regulating Resistors, but the resistors Rsnsl and Rsns2 are not.
  • the prior art PTAT circuits can provide well- behaved PTAT output current and the bandgap references can provide reasonably constant output Voltage with respect to changing temperature
  • the relatively low Voltage available across the resistors RW and/or RF means that the thermal noise current that is generated limits the short-term stability.
  • the signal-to- noise ratio can only be improved by increasing the operating current, and or by increasing the ratio of the Transistor areas.
  • the Voltage across the resistors RW and/or RF in Figures Ia, 2, and 3 depends only logarithmically on the current density ratio between the transistors QD:QW or QD:QF, it can be seen that the returns on increasing the Area Ratio become quite low once the current-density ratio is large.
  • the present invention seeks to improve the signal-to-noise and does so by improving the utilisation of the available currents.
  • a circuit for use in a current source or a proportional to absolute temperature sensor or in a bandgap regulator conducting a current comprising two parallel current branches each including at least one transistor and at least one resistor, and a control circuit for determining the relationship between the driving currents through the two branches, wherein a first transistor in the first branch has a higher effective current density flowing in use through its conductive area than the effective current density flowing in use through the conductive area of a second transistor in the second branch so as to develop control voltages (V B E) across the control terminals of the first and second transistors which differ from one another, the difference ( ⁇ V B E) between the two control voltages (V B E) being regulated by the voltage across at least a regulating resistor in the second branch, characterised in that at least a further regulating resistor is provided in the first branch, the voltage drop across which resistor regulates the effective difference in current densities between a third transistor and a reference transistor, and substantially the whole of at least one
  • GB 2,285,152 describes circuits that comprise the further regulating resistors of the present invention.
  • a regulating resistor is one in which the voltage developed across it directly modifies the ⁇ V BE voltage .
  • FIGs 1 to 4 are circuits described above detailing different prior art proposals, and Figures 5 to 16 show different circuits embodying the present invention
  • Figure 5 shows an arrangement according to the invention where the input current Ibia of Figure Ia, and shown again in figure 3, is supplied by the output of a similar but complementary PTAT cell. If the arrangement is symmetrical between the NPN and PNP sides, it effectively provides a 3-dB noise advantage in the output noise over a circuit that comprises a single bandgap cell and a noiseless current mirror or replicator. Clearly, the absence of additional noise due to the replication is an additional advantage of this arrangement.
  • One limitation of this circuit is that it requires additional bias Voltage to prevent the transistors QNWF and QPWF going into saturation (as generally defined for bipolar transistors) or into the triode region of operation (as generally defined for FET" s) .
  • the circuit of Figure 6a shows one method by which the additional bias Voltage required by the circuit of Figure 5 may be removed.
  • the Voltage sources VNbi and VNbi are used.
  • VPbi will usually be replaced by more complex circuitry that advantageously derives the base current from the emitter connections of the transistors QPW, QNW, and a small amount of power from some other supply - though the latter will not be necessary if suitable FET ' s are available.
  • FIG. 6b An example of a simple circuit configuration that uses FETs to bias the transistors is shown in Figure 6b. Different FET types are shown controlling the NPN and the PNP to illustrate bias for exemplary reasons only. It is noted in passing that the high impedance at the collectors of the Transistor pairs QND, QPW and QPD, QNW means that the arrangement is relatively non-critical as regards the noise Voltage of the bias arrangements VNbi and VPbi of Figure 5 and NMOS D and PJFET D of figure 6. In principle, one can stack the composite current sources of Figures 5 and 6 to further improve the noise performance. This requires the output impedances of the component sources of Figures 5 and 6 to be similar in order for the total output noise not to be dominated by the noise of either one. This will be considered later, but first arrangements according to the present invention will be considered that can further improve the noise within headroom similar to that required by the circuit of Figure 5.
  • the noise advantage is obtained by virtue of sensing the current in each main current branch using Resistors that exploit the full difference between the base- emitter Voltages "VBE" of the respective pairs of Transistors QND and QNWF or QNW, and QPD and QPWF or QW.
  • the arrangements increase the total Voltage across the sensing resistors, or that the arrangements stabilise the currents in each of the current branches separately by using the full difference between the base emitter Voltages of the Transistors QND and QPD and the other illustrated Transistors of the same polarity.
  • the principle underlying all embodiments of the invention resides in the use of currents in both the Branches to generate voltages across the Regulating Resistors to generate a total power in the Regulating Resistors that exceeds the power that could be achieved in Regulating Resistors that could be incorporated in a single side of a Current Source. Indeed, given that the signal to noise ratio in the sensor (or Regulator) Resistors
  • Figure 7 shows an arrangement according to the invention that utilises Transistors of a single polarity.
  • Figure 8 illustrates a combination of the methods of Figures 5 and 7. This shows an improvement of up to 5.5 dB relative to prior art, but it does not appear that the approximately 200-mV additional headroom requirement compared with a single height circuit can usefully be removed using the methods of Figure 6.
  • Figure 9 shows the method of figure 7 applied to Brokaw' s arrangement.
  • Figures 10 and 11 show ways of utilising series groups based on the arrangement of Figure 7 to produce lower noise currents than would be available from a circuit that occupies a single diode height.
  • Figure 12 shows the methods of figures 10 and 11 incorporated jointly with that of Figure 5 in a new bandgap regulator.
  • the regulator is configured to produce an output Voltage that is equal to three silicon bandgaps plus one Schottky bandgap, or about 3.8 Volts.
  • the forward Voltage of the Schottky diode may advantageously be incorporated into the input offset Voltage of the amplifier by placing it within the amplifiers input stage. It is to be understood that this is a portmanteau implementation, and that any of the arrangements incorporated may be omitted or replaced with other PTAT or amplification arrangements in order to match a particular output requirement.
  • Figure 13 shows an arrangement that is essentially two of the Figure 8 arrangements stacked.
  • the version as shown uses the symmetry of the arrangement to allow the connections shown as ctrlF, ctrlD and ctrlW, which have be joined in the arrangement of Figure 8, to be separated. If the Transistors of like polarity match precisely, the current noise will be 3-dB lower than the arrangement of Figure 8. However, mismatches will generally cause the equilibrium current in the upper or lower half to be greater than that in the other; the half with the greater equilibrium current will then saturate, and the performance will be little if any better than the performance of the PTAT of Figure 8. Accordingly, some form of feedback is required to render both stages in the proper operational region and achieve the desired noise improvement.
  • a simple arrangement that provides the required stabilisation is to provide feedback resistors around the Collector-Base terminals of some or all of the transistors QPFh, QnFh, QPFi and QNFi, the requirement being that the arrangements for the top and bottom halves result in the halves having similar dynamic impedances.
  • the downside of this is that the resistors contribute both to the supply sensitivity and also additional noise. If a suitable external bias point is available, resistors may be connected between the terminals ctrlF, ctrlD and ctrlW such as to equalise the currents of the cells; such resistors will contribute negligible noise provided that the gain is corrected to account for their effects, and both halves of the circuit are maintained in their proper operating condition.
  • Noise on the external bias point will also be well attenuated, at least at low frequencies.
  • the signals from some or all the ports ctrlF, ctrlD and ctrlW may be used to generate currents that are injected into some other point in the cells; an example would be the bases of QPFh and QNFi. These signals would be antiphase currents .
  • Figure 14 shows an arrangement derived from figure 8 that is particularly suitable for use in bandgap regulators.
  • An amplifier Amp with an inbuilt input offset Voltage Vos that is shown external to the amplifier is used to set up the Voltage between the collector and the emitter of the transistor QNW such that the current from the collector to the emitter is adequately maintained.
  • this could be a PTAT Voltage generated by running the amplifiers input transistors at different current densities.
  • the PTAT current generated is passed through the resistor RPTAT to generate the major contribution to the PTAT Voltage that compensates the temperature coefficient of the transistor base-to-emitter Voltage.
  • the Voltage across RNW also contributes to the PTAT Voltage; this can provide a further noise advantage, as the transistors that drive RNW present a relatively low impedance.
  • Figure 15 extends the principle of figure 14, using the Voltage across RPW and the base to emitter Voltage of Qsns to provide bias for QNW.
  • Qsns serves as the first amplification stage of the bias circuit, and in principle can provide lower input noise Voltage than would an input pair that was operated at the same current.
  • An additional advantage is that the relatively low noise Voltages that the circuit applies to both RNW and RPW contribute to the final bandgap potential.
  • Figure 16 shows an exemplary arrangement that places two of the bandgap circuits of figure 15 effectively in series.
  • the regulation current from the amplifier Amp can provide current to drive external load, and the amplifier output AmpH corrects the bias for the upper circuit.
  • the choice of which amplifier provides the external load current will depend on the design of the amplifiers, and the arrangement is readily adapted for higher output Voltages.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Power Engineering (AREA)
  • Nonlinear Science (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Control Of Electrical Variables (AREA)

Abstract

La présente invention concerne un circuit pour une utilisation dans une source de courant ou dans un capteur proportionnel à la température absolue (PTAT) ou dans un régulateur de bande interdite conduisant un courant. Le circuit comprend une cellule PTAT comportant deux dérivations de courant en parallèle comprenant chacune au moins un transistor et au moins une résistance, et un circuit de commande permettant de déterminer la relation entre les courants de commande sur les deux dérivations. Un premier transistor dans la première dérivation présente une densité de courant efficace en circulation pendant l’utilisation sur sa zone conductrice plus grande que celle sur la zone conductrice d’un deuxième transistor dans la seconde dérivation de façon à développer des tensions de commande (VBE) sur les bornes de commande des premier et deuxième transistors qui diffèrent l’une de l’autre, la différence (VBE) entre les deux tensions de commande (VBE) étant régulée par la tension sur au moins une résistance de régulation dans la seconde dérivation. Dans l’invention, au moins une résistance de régulation supplémentaire est prévue dans la première dérivation, la chute de tension sur cette résistance régulant la différence efficace des densités de courant entre un troisième transistor et un transistor de référence, et sensiblement la totalité d’au moins une tension VBE est développée sur une résistance de régulation ou des résistances dans chacune des deux dérivations pour chaque VBE complète d’un potentiel nécessaire pour polariser le circuit dans son état de fonctionnement.
EP08788717A 2008-08-28 2008-08-28 Circuit sensible à la température Withdrawn EP2329230A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/GB2008/050746 WO2010023421A1 (fr) 2008-08-28 2008-08-28 Circuit sensible à la température

Publications (1)

Publication Number Publication Date
EP2329230A1 true EP2329230A1 (fr) 2011-06-08

Family

ID=40637726

Family Applications (1)

Application Number Title Priority Date Filing Date
EP08788717A Withdrawn EP2329230A1 (fr) 2008-08-28 2008-08-28 Circuit sensible à la température

Country Status (2)

Country Link
EP (1) EP2329230A1 (fr)
WO (1) WO2010023421A1 (fr)

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3617859A (en) 1970-03-23 1971-11-02 Nat Semiconductor Corp Electrical regulator apparatus including a zero temperature coefficient voltage reference circuit
US3659121A (en) 1970-11-16 1972-04-25 Motorola Inc Constant current source
JPS4854460A (fr) * 1971-11-11 1973-07-31
US3887863A (en) 1973-11-28 1975-06-03 Analog Devices Inc Solid-state regulated voltage supply
US3930172A (en) * 1974-11-06 1975-12-30 Nat Semiconductor Corp Input supply independent circuit
US4447784B1 (en) 1978-03-21 2000-10-17 Nat Semiconductor Corp Temperature compensated bandgap voltage reference circuit
US5627461A (en) 1993-12-08 1997-05-06 Nec Corporation Reference current circuit capable of preventing occurrence of a difference collector current which is caused by early voltage effect
JP2800720B2 (ja) * 1995-05-19 1998-09-21 日本電気株式会社 起動回路

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
None *
See also references of WO2010023421A1 *

Also Published As

Publication number Publication date
WO2010023421A1 (fr) 2010-03-04

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