CN101013332A - Ultra-low voltage reference source - Google Patents

Abstract

The invention discloses a low-voltage reference source circuit. The circuit includes the PTAT current generating circuit, the start circuit and the low-voltage reference generating circuit; the PTAT current generating circuit is used to generate a current proportional to absolute temperature, and the current is the ratio of the thermal voltage of PN junction and the resistance inside; the current mirroring to the low-voltage reference generating circuit; the start circuit is used to cut the working point of zero current, and after power-on, it provides nonzero initial current for the low-voltage reference generating circuit, and guides it entering stable state, to achieve the normal start of the circuit; the low-voltage reference generating circuit mirroring a current proportional to the temperature, and generating a low pressure drop through the resistor, to provide the low-voltage reference voltage. This voltage reference source circuit is based on the thermal voltage of bipolar junction transistors, to generate the reference voltage with a certain proportion of the voltage. This voltage reference source circuit of the invention is simple and low cost, and it can provide a stable, lowing to 10mV reference voltage for integrated circuits at different temperatures and different supply voltages.

Description

A kind of ultra-low voltage reference source

Technical field

The invention belongs to the voltage reference technology, be specifically related to a kind of ultra-low voltage reference source, it is particularly useful for integrated circuit.

Background technology

In integrated circuit, the input voltage and the some fixing reference voltages that often need to sample compare.Circuit designers wishes that all this fixing reference voltage fixes at any time, promptly is not subjected to the influence of extraneous factor, such as deviation of the variation of supply voltage, circuit working variation of temperature, integrated circuit fabrication process or the like.

But in actual conditions, can't make the reference voltage source that is not subjected to mains voltage variations fully, also can't realize the reference voltage of zero-temperature coefficient.It is enough little that we wish that just supply voltage and temperature are reduced to the influence of reference voltage, under existing manufacturing process situation, and the deviation that reduces integrated circuit fabrication process of matching and the symmetry by circuit as far as possible.

The mode of the reference voltage that current generation is fixing mainly contains two kinds: first kind is band-gap reference source circuit more commonly, it mainly based on the voltage addition with the voltage and a negative temperature coefficient of a positive temperature coefficient (PTC), has produced a temperature independent zero-temperature coefficient voltage; Second kind is directly to adopt the Zener diode voltage stabilizing.These two kinds of methods can produce high-precision reference voltage, but the greatest drawback that exists is: the reference source circuit that can't realize extra low voltage.Negative temperature coefficient voltage utilization in the band-gap reference source circuit be the base stage of bipolar transistor and the voltage difference VBE of emitting stage, this voltage is about about 0.7V usually, therefore the reference voltage that constitutes can not be very low.Generally, the reference voltage that adopts this principle to constitute is generally 1.2V.What the pressure stabilization function of Zener diode adopted is the breakdown reverse voltage of diode, because the restriction of technology, this voltage can not be too low.

Yet in actual the use, may need a very low reference voltage, such as at tens millivolts.So low voltage can't rely on traditional method to realize.

Summary of the invention

The object of the present invention is to provide a kind of ultra-low voltage reference source, the reference voltage that this voltage reference source provides is low to moderate and can compares with the thermal voltage of PN junction, and changes at input voltage, can provide a constant reference voltage under the different operating temperature.

A kind of ultra-low voltage reference source circuit provided by the invention is characterized in that: this circuit comprises and is proportional to absolute temperature current generating circuit, start-up circuit and low pressure reference generating circuit;

Wherein, be proportional to the absolute temperature current generating circuit and be used to produce one and be proportional to the absolute temperature electric current, this electric current is the thermal voltage of PN junction and the ratio of resistance wherein; This current mirror is to the low pressure reference generating circuit; Start-up circuit is used for the working point of degeneracy zero current, and the back that powers on provides the non-zero initial current for the low pressure reference generating circuit, guides it to enter steady state (SS), realizes the normal startup of circuit; Low pressure reference generating circuit mirror image goes out an electric current that is proportional to temperature, and produces low pressure drop by resistance, and the low pressure reference voltage is provided.

Generally, along with the rising of temperature, thermal voltage can rise with the speed of every degree centigrade of 0.085mV.If select for use the resistance of negative temperature coefficient to cooperate, can design and produce the reference voltage under the zero-temperature coefficient under certain temperature with thermal voltage.PN junction thermal voltage VT under the room temperature is 26mV, based on this voltage, produces a voltage suitable with this voltage, thereby realizes ultra-low voltage reference source.The present invention is based on the bipolar junction transistor technology, utilized the thermal voltage of PN junction,, obtain one and the proportional reference voltage of thermal voltage by computing and processing of circuit.Because the thermal voltage of PN junction does not change with PN junction voltage, therefore, obtain a reference voltage that has nothing to do with external voltage easily.Thermal voltage is the minorant of device temperature, and reference voltage source circuit of the present invention is simple, realizes that cost is low, can provide reference voltage stable, that can be low to moderate the 10mV level to integrated circuit under different temperatures He under the different electrical power voltage.

Description of drawings

Fig. 1 is the circuit diagram of ultra-low voltage reference source of the present invention;

Fig. 2 is the improved ultra-low voltage reference source circuit diagram of the present invention.

Specific embodiments

The present invention is further detailed explanation below in conjunction with accompanying drawing and example.

As shown in Figure 1, the ultra-low voltage reference source circuit comprises the current branch that three current mirroring circuits that are made of the PNP bipolar junction transistor are formed: be proportional to absolute temperature current generating circuit (being the PTAT current generating circuit) 1, start-up circuit 2 and low pressure reference generating circuit 3.

PTAT current generating circuit 1 is used to produce a PTAT electric current, and this electric current is the thermal voltage of PN junction and the ratio of resistance wherein, is directly proportional with the current amplification factor of PNP bipolar junction transistor and NPN bipolar junction transistor simultaneously.PTAT current generating circuit 1 is an auto bias circuit, has two stable current work points.

Start-up circuit 2 is used for the working point of degeneracy zero current, realizes the normal startup of circuit.

Low pressure reference generating circuit 3 is used to produce the low pressure reference voltage.

PTAT current generating circuit 1 produces an electric current that is proportional to temperature, and this electric current goes out an electric current that is proportional to temperature by low pressure reference generating circuit 3 mirror images, and current flowing resistance produces low pressure drop, and the low pressure reference voltage is provided.Start-up circuit 2 for low pressure reference generating circuit 3 provides the non-zero initial current, guides it to enter steady state (SS) behind power supply electrifying, realizes the startup of entire circuit.

PTAT current generating circuit 1 is by PNP transistor Q1, and resistance R 1 and NPN transistor Q4 are composed in series, and the base stage that the voltage on the resistance R 1 is reduced to NPN transistor Q4 provides biasing.

Start-up circuit 2 is made of resistance R 5 and capacitor C 1 series connection.

Low pressure reference generating circuit 3 is made of two parts, and first is by PNP transistor Q2, and NPN transistor Q5 is composed in series, and base stage and the collector of PNP transistor Q2 are connected to form the diode form; Second portion is composed in series by PNP transistor Q3 and resistance R 3, and PNP transistor Q2 and Q3 constitute the current mirror relation.

The collector of NPN transistor Q4 in the PTAT current generating circuit 1 links to each other through the NPN transistor Q5 of resistance R 2 and low pressure reference generating circuit 3 and provides biasing for NPN transistor Q5.PNP transistor Q2 collector in the low pressure reference generating circuit 3 links to each other with the base stage of PNP transistor Q1 in the PTAT current generating circuit 1, drives its base stage, produces the electric current that becomes mirror with the Q2 collector current in the collector of PNP transistor Q1.Resistance R 5 in the start-up circuit 2 connects the collector of PNP transistor Q2 in the low pressure reference generating circuit 3, for circuit start provides the non-zero initial current.

After powering on, power supply is formed the path of power supply to ground through PNP transistor Q2, resistance R 5, the capacitor C 1 of diode connected mode, can produce electric current in the branch road at PNP transistor Q2 place.

Because the current mirror of PNP transistor Q2 and Q1 relation has also produced electric current, driving transistors Q4 and Q5 conducting in the branch road at Ql place.Produce electric current among the PTAT current generating circuit l, realized the startup of PTAT current generating circuit l.Because the effect of capacitor C l, when the electric current in the circuit reach stable after, the electric current that flows through on the resistance R 5 is almost O, it can not have influence on the operate as normal of circuit.

In the circuit of Fig. 1, make the emitter area of PNP transistor Q1, Q2, Q3 identical, then:

I _B1＝I _B2＝I _B3 (1)

I _C1＝I _C2＝I _C3 (2)

Simultaneously:

I _C5＝I _B1+I _B2+I _B3+I _C2 (3)

I _B＝I _C/β (4)

Wherein, β is the ratio of collector current and base current in the transistor, i.e. current amplification factor.So:

$I_{C5}=(1+\frac{1}{{\mathrm{\β}}_{\mathrm{PNP}}})I_{C1}---\left(5\right)$

I _C1＝I _B4+I _C4+I _B5 (6)

I _C4＝I _C1-I _B4-I _B5

$=I_{C1}-\frac{I_{C4}}{{\mathrm{\β}}_{\mathrm{NPN}}}-I_{B5}---\left(7\right)$

Can get by (5) and (7):

$I_{C4}=\frac{{\mathrm{\β}}_{\mathrm{NPN}}-1-\frac{3}{{\mathrm{\β}}_{\mathrm{PNP}}}}{1+{\mathrm{\β}}_{\mathrm{NPN}}}{I}_{C1}---\left(8\right)$

Make R2=2R1, then first current branch and second current branch have following relation among Fig. 1:

V _A＝V _BE4＝V _BE5+I _B5R2+(I _B5+I _C4)R1

＝V _BE5+(2I _B5+I _B5+I _C4)R1 (9)

ΔV _BE＝V _BE4-V _BE5＝R1(3I _B5+I _C4) (10)

Simultaneously:

${\mathrm{\ΔV}}_{\mathrm{BE}}=V_T\ln \frac{I_{C4}{A}_{E5}}{I_{C5}{A}_{E4}}---\left(11\right)$

V wherein _TBe transistorized thermal voltage.Can get by (5), (8), (10) and (11):

$I_{\mathrm{<figure-callout\; id="3"\; label="C"\; filenames="A20061012513000091.png"\; state="\{\{state\}\}">C</figure-callout>}3}={\mathrm{<figure-callout\; id="1"\; label="I\; C"\; filenames="A20061012513000091.png"\; state="\{\{state\}\}">I</figure-callout>}}_C=\frac{V_T\ln [\frac{{\mathrm{\&beta;}}_{\mathrm{NPN}}{\mathrm{\&beta;}}_{\mathrm{PNP}}-{\mathrm{\&beta;}}_{\mathrm{PNP}}-3}{({\mathrm{\&beta;}}_{\mathrm{NPN}}+1)({\mathrm{\&beta;}}_{\mathrm{PNP}}+3)}\&CenterDot;\frac{A_{E5}}{A_{E4}}]}{3-\frac{1+3/{\mathrm{\&beta;}}_{\mathrm{PNP}}}{{\mathrm{\&beta;}}_{\mathrm{NPN}}}+\frac{{\mathrm{\&beta;}}_{\mathrm{NPN}}-1-3/{\mathrm{\&beta;}}_{\mathrm{PNP}}}{1+{\mathrm{\&beta;}}_{\mathrm{NPN}}}}\&CenterDot;\frac{1}{R1}---\left(12\right)$

Then:

V _REF＝I _C3·R3 (13)

By (12) and (13) formula, can draw a reference voltage with independent of power voltage:

$V_{\mathrm{REF}}=\frac{V_T\ln [\frac{{\mathrm{\&beta;}}_{\mathrm{NPN}}{\mathrm{\&beta;}}_{\mathrm{PNP}}-{\mathrm{\&beta;}}_{\mathrm{PNP}}-3}{({\mathrm{\&beta;}}_{\mathrm{NPN}}+1)({\mathrm{\&beta;}}_{\mathrm{PNP}}+3)}\&CenterDot;\frac{A_{E5}}{A_{E4}}]}{3-\frac{1+3/{\mathrm{\&beta;}}_{\mathrm{PNP}}}{{\mathrm{\&beta;}}_{\mathrm{NPN}}}+\frac{{\mathrm{\&beta;}}_{\mathrm{NPN}}-1-3/{\mathrm{\&beta;}}_{\mathrm{PNP}}}{1+{\mathrm{\&beta;}}_{\mathrm{NPN}}}}\&CenterDot;\frac{R3}{R1}---\left(14\right)$

Generally, β _NPNAnd β _PNPBigger, (14) formula is simplified and can be obtained:

$V_{\mathrm{REF}}=\frac{R3}{R1}{V}_T\ln \left(\frac{A_{E5}}{A_{E4}}\right)---\left(15\right)$

The meaning of each symbol of using in the above-mentioned formula is described as follows:

I _B1The base current of expression PNP transistor Q1, wherein, symbol I represents electric current, subscript B represents base stage, the numbering of subscript 1 expression transistor correspondence, I _B2, I _B3The meaning of symbol can be analogized according to inferior principle.

I _C1: the collector current of expression PNP transistor Q1, I represents electric current in the symbol, subscript C represents collector, the numbering of subscript 1 expression transistor correspondence, I _C2, I _C3The meaning of symbol can be analogized according to inferior principle.

β _NPN: the current amplification factor of expression NPN transistor correspondence, wherein, β represents current amplification factor, subscript NPN represents the transistor of NPN type.β _PNPThe current amplification factor of expression PNP transistor correspondence.

V _REF: expression low pressure reference voltage, this is that the present invention is resulting.

V _BE4: the emitter junction voltage of expression transistor Q4, it and thermodynamic temperature T are inversely proportional to

V _BE5: the emitter junction voltage of expression transistor Q5, it and thermodynamic temperature T are inversely proportional to.

Δ _BE: the emitter junction voltage difference of expression transistor Q4 and Q5, its direct ratio and thermodynamic temperature T.

V _A: the voltage of expression node A.

V _T: the thermal voltage of expression PN junction.

A _E5: the emitter junction area of expression transistor Q5.

A _E4: the emitter junction area of expression transistor Q4.

R1, R2, R3: represent resistance R 1 respectively, the resistance value of R2 and R3 correspondence.

If R3 and R1 adopt resistance of the same type, the temperature coefficient of this reference voltage is the temperature coefficient of thermal voltage VT.Generally, this temperature coefficient is 0.085mV/C.

For above-mentioned design concept, if expect the reference voltage of zero-temperature coefficient under the room temperature, can select for use the resistance of negative temperature coefficient to be R3, be R1～R2 with the resistance of positive temperature coefficient (PTC).

When the circuit of Fig. 1 has realized that supply voltage VCC changes on a large scale, provide a constant relatively output voltage V _REFThis output voltage is numerically comparable with transistorized thermal voltage, can provide common band gap reference voltage the extra low voltage that can not provide.

When supply voltage rises to when higher,, cause output reference voltage also to increase on year-on-year basis because the influence of transistorized Early voltage makes reference current increase.For increasing the precision of reference voltage, can select the big integrated circuit realization technology of Early voltage to produce this reference voltage.

In addition, from the second portion of low pressure reference generating circuit 3 as can be seen, the direct voltage difference of the collector and emitter of Q3 is the poor of supply voltage and output reference voltage.Because the latter is very little, makes VCE3 increase with the increase of supply voltage, has further increased the electric current of the 3rd current branch.Because the error that Early voltage brings can add the transistor that a diode connects in the 3rd current branch, reduced the error that the output current branch road brings owing to mains voltage variations, the coupling of having accomplished 3 built-up circuits simultaneously for reducing to export branch road.As shown in Figure 2, the NPN transistor Q6 and the resistance R 4 of series diode connected mode between the collector of the resistance R 3 of low pressure reference generating circuit 3 and PNP transistor Q3.

Claims (3)

1, a kind of ultra-low voltage reference source circuit is characterized in that: this circuit comprises and is proportional to absolute temperature current generating circuit (1), start-up circuit (2) and low pressure reference generating circuit (3);

Wherein, be proportional to absolute temperature current generating circuit (1) and be used to produce one and be proportional to the absolute temperature electric current, this electric current is the thermal voltage of PN junction and the ratio of resistance wherein; This current mirror is to low pressure reference generating circuit (3); Start-up circuit (2) is used for the working point of degeneracy zero current, and the back that powers on provides the non-zero initial current for low pressure reference generating circuit (3), guides it to enter steady state (SS), realizes the normal startup of circuit; Low pressure reference generating circuit (3) mirror image goes out an electric current that is proportional to temperature, and produces low pressure drop by resistance, and the low pressure reference voltage is provided.

2, ultra-low voltage reference source circuit according to claim 1 is characterized in that:

The described absolute temperature current generating circuit (1) that is proportional to is by PNP transistor Q1, and resistance R 1 and NPN transistor Q4 are composed in series, and the base stage that the voltage on the resistance R 1 is reduced to NPN transistor Q4 provides biasing;

Start-up circuit (2) is made of resistance R 5 and capacitor C 1 series connection;

Low pressure reference generating circuit (3) is made of two parts, and first is by PNP transistor Q2, and NPN transistor Q5 is composed in series, and base stage and the collector of PNP transistor Q2 are connected to form the diode form; Second portion is composed in series by PNP transistor Q3 and resistance R 3, and PNP transistor Q2 and Q3 constitute the current mirror relation;

The collector of NPN transistor Q4 links to each other with NPN transistor Q5 through resistance R 2, and provides biasing for NPN transistor Q5; PNP transistor Q2 collector links to each other with the base stage of PNP transistor Q1, drives its base stage, produces the electric current that becomes mirror with the Q2 collector current in the collector of PNP transistor Q1; Resistance R 5 connects the collector of PNP transistor Q2, for circuit start provides the non-zero initial current.

3, ultra-low voltage reference source circuit according to claim 2 is characterized in that: in low pressure reference generating circuit (3), and the NPN transistor Q6 of resistance in series R4 and diode connected mode successively between the collector of PNP transistor Q3 and resistance R 3.

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