CN102722210A - Nonlinear correction circuit for band-gap reference - Google Patents

Abstract

The invention discloses a nonlinear correction circuit for band-gap reference. The form of the output current of the nonlinear correction circuit is TlnT. When the nonlinear correction circuit is used for a curvature correction circuit, the circuit compensates the inherent nonlinearity accurately.

Description

A kind of nonlinearity correction circuit that is used for band-gap reference

Technical field

The present invention is that a kind of monolithic integrated optical circuit that relates to band-gap reference, especially output current form are the nonlinearity correction circuit that is used for band-gap reference of TlnT.

Background technology

A/D, D/A converter, temperature sensor, various systems such as measuring system and voltage stabilizer use reference circuit to set up the accuracy of this system.Generally, reference circuit has following two types: band-gap reference or Zener benchmark.

With respect to about 7 volts voltage breakdown, the Zener diode benchmark needs about 10 volts voltage to reach suitable opereating specification.Yet the development trend of microelectronic industry is to reduce supply voltage, and with 5 volts of supply voltage standardization.Consequently reduce the number that is suitable for the Zener baseline system, also need a benchmark accurately simultaneously.Band-gap reference is the first choice circuit that can satisfy precision and single 5 volts of power supply double requirements.Yet the degree of accuracy of band-gap reference requires increasingly high, and especially an urgent demand improves the precision with respect to temperature linearity.

The characteristic of in this, looking back traditional band-gap reference is favourable with approximate output.Fig. 1 is a kind of schematic diagram of traditional band-gap reference circuit 10, and its form is simple relatively and band-gap reference is relatively accurate, i.e. the Bu Luokao unit.

In the Bu Luokao unit, resistance R 1, the resistance of R2 and operational amplifier A 1 are selected, so that NPN transistor Q1 and Q2 work under the situation that collector current equates.Secondly, the emitter junction area of Q1 and Q2 is than being A, and when Q1 and Q2 worked under the equal situation of collector current, the base-emitter voltage Vbe of Q1 was low than the base-emitter voltage of Q2.The 3rd, the value of R3 two ends pressure drop VR3 is the difference Δ Vbe of the base-emitter voltage of transistor Q1 and Q2.As everyone knows, it is " PTAT " voltage that such voltage difference is directly proportional with absolute temperature, and its form is following:

Wherein A is the Q1 that selectes and the current density ratio of Q2, because they work under identical levels of current, so A also is the emitter junction area ratio of Q1 and Q2.The 4th, because I4=I1+I2=2I2, so the voltage ratio VR4/VR3 at resistance R 4 and R3 two ends is provided by formula G=VR4/VR3=2R4/R3.

Simultaneously, the benchmark output voltage V out of transistor Q2 base stage is base-emitter voltage Vbe and the VR4 sum of Q2.Because VR4 is big more than VR3, and VR3 is the voltage that depends on temperature, so output voltage V out can be expressed as

$\mathrm{Vout}=\mathrm{Vbe}+\mathrm{VR}4=\mathrm{Vbe}+\mathrm{GVR}3=\mathrm{Vbe}\frac{2R4}{R3}\frac{\mathrm{KT}}{q}\ln A$

In practical application, if ratio R4/R3 selects suitably, make the VR3 that is directly proportional with temperature offset the Vbe that is inversely proportional to temperature, then will obtain an accurate and stable relatively benchmark output voltage V out.

Although above-described circuit has obtained relatively accurate output, band-gap reference output also might be non-linear because of the influence of two temperature source.

First non-linear source relates to the use of diffusion resistance in the band-gap reference.Diffusion resistance has very high temperature coefficient, greatly between 1000 to 3000PPM/ ℃, thereby causes reference voltage that significantly curvature is arranged.Yet the temperature coefficient of sheet resistances such as nickel-chrome or silicochromium resistance is lower, and their use can be to a great extent with the non-linear elimination relevant with resistance.

Second non-linear source is that more scabrous general type is the inherent error item of TlnT at present.The form of band-gap reference output voltage that comprises this error term is following:

$\mathrm{Vout}=C1\frac{\mathrm{KT}}{q}+\mathrm{Vgo}(1-\frac{T}{\mathrm{To}})+\mathrm{Vbeo}\frac{T}{\mathrm{To}}+\frac{\mathrm{KT}}{q}\ln \frac{\mathrm{Ic}}{\mathrm{Ico}}+\frac{\mathrm{nKT}}{q}\ln \frac{T}{\mathrm{To}}$

Differentiate gets following formula to temperature:

$\frac{\mathrm{dVout}}{\mathrm{dT}}=\frac{C1K}{q}-\frac{\mathrm{Vgo}}{\mathrm{To}}+\frac{\mathrm{Vbeo}}{\mathrm{To}}+\frac{\mathrm{nKT}1}{q}\frac{1}{T}-\frac{\mathrm{nK}}{q}\ln \frac{T}{\mathrm{To}}+\frac{K}{q}\ln \frac{\mathrm{Ic}}{\mathrm{Ico}}=f\left(T\right)$

Wherein: the C1=constant,

The K=Boltzmann constant,

The q=electron charge,

The band gap voltage of Vgo=silicon,

Temperature when To=measures Vbeo,

Collector current is the base-emitter voltage of the silicon transistor of Ico under the Vbeo=To temperature,

The transistorized collector current of Ic=(nominally being the function of temperature),

N=constant (being about 2)

The T=Kelvin temperature.

In the item number that all differentiates obtain, all the other are all temperature independent except last two.In practical application, the summation of all item numbers of following formula at room temperature is approximately zero.Yet, because last two, temperature coefficient still can not be zero under all temperature.

Specifically, for (nK/q) ln (T/To) second from the bottom of equality 4, at-55 ℃, 25 ℃ during with 125 ℃, this value is respectively-49 μ V/ ℃, and 0 and+49 μ V/ ℃.This show temperature by-55 ℃ be increased to+125 ℃ the time, this has changed 98 μ V/ ℃.This has produced one about 82ppM/ ℃ variation, because reference voltage itself is about 1.2 volts, so limited its application under high precision, wide temperature range.

Because opposite in sign is so second nonlinear terms (K/q) ln (Ic/Ico) can be used for eliminating first nonlinear terms.When Ic=Ico (T/To) n, will offset fully for these two.This transistorized operating current expression formula is to correct one of band-gap reference circuit non-linear method, but correcting circuit is implemented complicacy, and in relative broad range, works and also can bring problem for the operation of circuit.

On May 1 nineteen eighty-two, Pi Si has delivered the paper of a piece " a kind of novel Celsius temperature sensor " by name in " Circuits and Systems alliance " that PASADENA, Calif. is published, proposed a kind of curvature correction circuit that is used for temperature sensor.It is the nonlinear terms of TlnT with the correction form that this sensor adopts a T2 generator circuit.The T2 generator circuit is shown in the system among Fig. 2 20.In brief, the electric current (IPTAT) that is admitted to transistor Q1 and Q2 is directly proportional with absolute temperature, and the electric current that is loaded on the Q3 is a constant with respect to temperature.The value of correcting current I4 through Q4 be (I1 * I2)/I3, wherein I1 and I2 are the IPTAT through Q1 and Q2, I3 is the electric current through Q3.That is to say that I4 is directly proportional with IPTAT2, promptly be directly proportional with T2.This T2 curvature compensation circuit is used to add to temperature sensor circuit.Yet, should be pointed out that T2 curvature compensation circuit 20 is not a real band gap correcting circuit.The applicant knows that circuit 20 is the simplest, perhaps is the most effective T2 temperature curvature compensating circuit.Although the T2 item is similar to the error term of band-gap reference, band-gap reference has departed from the T2 item, especially at a lower temperature.Therefore, a kind of generally better band-gap reference nonlinearity correction circuit should produce a TlnT item.

Unfortunately, considerably less in the work of being done aspect the solution nonlinear problem.The circuit that at present known only is is used to produce the TlnT item comprises A/D converter, band-gap reference and correcting circuit.Correcting circuit is complicated, yet the objective of the invention is to obtain simple relatively and effective curvature correction circuit.

Therefore, remove few exceptions, band-gap reference does not have available curvature correction technology.This is unfortunate: because temperature coefficient itself is the function of temperature, nonlinear TlnT error term has limited the minimum temperature coefficient that can obtain.To be significantly improved about the performance of temperature drift through eliminating this nonlinear terms bandgap reference.

Summary of the invention

Circuit or method that to the invention provides a kind of output current form be TlnT.

Second purpose of the present invention provide easily and with/or the circuit or the method for circuit interface, this and circuit are embedded into band-gap reference circuit and this band-gap reference circuit can produce the curvature correction electric current that general type is TlnT.

The 3rd purpose of the present invention provides the circuit or the method for the curvature correction electric current that can produce the above-mentioned type, and with respect to linear element, circuit is optimized nonlinear element through the selection of conventional transistor.

The 4th purpose of the present invention provides circuit or the method for correcting current by the decision of the base-emitter difference between current of conventional bipolar transistor, and the selection of the collector current that the ratio of non-linear current and linear current can be through bipolar transistor and the ratio of emitter area is optimized.

Technical solution of the present invention

Above-mentioned and other purposes embody in a kind of circuit that comprises a pair of bipolar transistor better, and transistorized collector current is I1 and I2, and I1 directly is directly proportional with temperature.It is the electric current of TlnT that above-mentioned transistorized base stage connects so that form to be provided through selected resistance.Collector current is provided by current feedback circuit, and wherein first electric current has essential temperature coefficient, and second electric current is zero-temperature coefficient.

The base stage of the 3rd bipolar transistor links to each other with base stage with first transistorized collector respectively with emitter in the circuit, being the electric current of TlnT through the 3rd transistor output form.

In addition, the present invention includes first and second parts.First comprises the band-gap reference circuit of the linear function that is output as temperature; Wherein a pair of bipolar transistor produces an output current on the different basis of base-emitter voltage; The output of feedback amplifying return circuit is connected to the right base stage of bipolar transistor, and a reverse input is arranged.Second portion is a curvature correction circuit that is used for band-gap reference; Comprise second pair of bipolar transistor; The area of their emitters is I1/I2 than the current ratio for A1/A2 and collector, and the resistance that base stage is R through a value links to each other and is directly proportional with absolute temperature and general type is the electric current of TlnT to produce one.This logarithmic term is relevant with the emitter area and the collector current of second pair of bipolar transistor.So as long as select electric current and area than suitable transistor, the nonlinear terms of correcting current can be easy to optimised with respect to linear term.

Description of drawings

Fig. 1 is a kind of traditional band-gap reference circuit synoptic diagram.

Fig. 2 is traditional band-gap reference circuit synoptic diagram that a kind of generation comprises T2 item correcting current.

Fig. 3 is a kind of curvature correction circuit diagram that obtains according to the present invention.

Embodiment

Fig. 3 is a kind of curvature correction circuit 30 synoptic diagram that are used for band-gap reference that obtain according to the present invention, and it produces the correction term that form is TlnT.Correcting circuit 30 as shown in Figure 3 produces the TlnT correction term and has only used four transistor Q41-Q44.This simple circuit can be connected to suitable band-gap reference circuit node through output current Io, so just has been embedded in the band-gap reference correcting circuit at an easy rate.As shown in the figure, current feedback circuit 41 and 42 produces IPTAT electric current I 41 and non-IPTAT electric current I 42 respectively, and wherein I42 is a zero-temperature coefficient.The form of output current Io is by collector current I41 and the I42 of transistor Q41 and Q42, and the emitter junction area determines than A.Can draw from the analysis to circuit 30, the correcting current Io through transistor Q43 confirms by Δ Vbe/R41, and wherein, Δ Vbe is base-emitter voltage Vbe poor of transistor Q41 and Q42.The form of this electric current is:

The emitter area of A41=Q41 wherein

And the emitter area of A42=Q42

As previously mentioned, I41 is proportional to absolute temperature and its form is I1=Io T/To, and I42 is temperature independent.Therefore, the form of output current Io is:

$\mathrm{Io}=\frac{\mathrm{KT}}{\mathrm{qR}41}\ln \left(\frac{\mathrm{IoT}}{\mathrm{ToI}42}\frac{A42}{A41}\right)$

The form of this parabolic function is:

Io＝C1?TlnC2?T

C1=K/qR41 wherein,

The output calibration electric current I o of parabolic is the form of the non-linear TlnT of band gap just.Therefore, correcting circuit 30 can embed band-gap reference circuit at suitable node with output calibration electric current I o, to eliminate the curvature of band-gap reference.These simple four transistor correcting circuits 30 can be carried out its calibration function very exactly, embed the band-gap reference unit at an easy rate, and can easily adjust correcting value.Important parameter in the circuit is R41; IPTAT electric current I 41; Zero-temperature coefficient electrical current (OTC) I42; Emitter junction area ratio and the collector current ratio of transistor Q41 and Q42.Through adjusting above-mentioned area and current ratio, make electric current through R41 under all temperature greater than zero.

In order to realize the curvature correction of special datum circuit, can easily obtain accurate Io value through selection and make circuit non-linear resistance R 41.Select I41, I42, A41 and A42 value do not reduce to zero to guarantee Io.Yet Io should be as far as possible little, makes the non-linear partial of Io big as far as possible with respect to linear segment.This is because the non-linear partial of Io is used for curvature correction and linear segment is an additional band-gap reference error term.Nonlinear terms are independent of current ratio and the emitter junction area ratio of transistor Q41 and Q42, and linear term then is the function of these ratios.In order linear dimensions to be minimized and the nonlinear parameter maximization, under the minimum operation temperature of band-gap reference, should make the value of the value of I41/I42 greater than A42/A41.This makes the gamma correction item be optimized with respect to intrinsic linear term, and this adjustment is relatively easy, and except producing the TlnT correction term with a kind of simple relatively circuit, this is a major advantage of the present invention.

Claims (6)

1. nonlinearity correction circuit that is used for band-gap reference; It is characterized in that: a pair of bipolar transistor 1 and 2 base stage are that the resistance of R links to each other through resistance, and its collector loads input current respectively, circuit through above-mentioned resistance with selected form output current; Make transistorized collector current be respectively I1; I2, wherein I1 directly is directly proportional with temperature, and the form of above-mentioned output current through resistance is:

$\frac{\mathrm{KT}}{\mathrm{qR}}\ln \left(\frac{I1}{I2}\frac{A2}{A1}\right)$

Wherein K is a Boltzmann constant.

The T=Kelvin temperature

The q=electron charge

The emitter area of A1=transistor 1

The emitter area of A2=transistor 2;

And order the collector current of transistor 1 and 2 is provided is I1 and I2.

2. the nonlinearity correction circuit that is used for band-gap reference according to claim 1; It is characterized in that: the output current form is TlnT; Bipolar transistor 2 and 1 emitter area are than being A2/A1, and electric current I 1 is directly proportional with absolute temperature, and output current is generally the TlnT form like this; Than relatively large, under selected working temperature, current value is bigger like this than less relatively and collector current for the emitter area of selecting.

3. the nonlinearity correction circuit that is used for band-gap reference according to claim 2; It is characterized in that: the base stage of bipolar transistor 3 and emitter are connected respectively to the collector and the base stage of transistor 1, thereby on transistor 3, form the collector current of a TlnT form.

4. the nonlinearity correction circuit that is used for band-gap reference according to claim 2 is characterized in that: the collector of transistor 3 is connected to band-gap reference circuit so that output current to be provided.

5. according to claim 1 and the 2 described nonlinearity correction circuits that are used for band-gap reference; It is characterized in that: a pair of bipolar transistor produces an output current on the different basis of base-emitter voltage; The output of feedback amplifying return circuit is connected to the right base stage of bipolar transistor, and a reverse input is arranged.

6. the nonlinearity correction circuit that is used for band-gap reference according to claim 5 is characterized in that: resistance of emitter series connection of transistor 2 is to control effective emitter area.

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