CN101819449A - Subthreshold MOSFET band-gap reference source - Google Patents

Abstract

The invention discloses a subthreshold MOSFET band-gap reference source capable of resisting technical fluctuations, which is composed of a negative temperature coefficient current generating circuit, a start circuit, a positive temperature coefficient current generating circuit and a reference voltage generating circuit, wherein the negative temperature coefficient current generating circuit adopts a bulk potential modulation technique, the bulk end of the subthreshold NMOSFET (used for generating a negative temperature coefficient voltage) is separated from the substrate and connected with the output end of a modulated voltage generator of the invention. According to the actual technical fluctuation conditions, a rheostat in the modulated voltage generator is adjusted to generate an appropriate modulated voltage so as to compensate the subthreshold NMOSFET threshold voltage variations caused by technical fluctuations, thereby greatly reducing the unfavorable effect of the technical fluctuations on the output reference voltage of the subthreshold MOSFET band-gap reference source.

Description

Subthreshold MOSFET band-gap reference source

Affiliated technical field

The present invention relates to a kind of subthreshold MOSFET band-gap reference source, belong to technical field of integrated circuits.

Background technology

Aspect bandgap voltage reference, the problem that needs to solve comprises: 1, along with the CMOS process constantly dwindles, the performance degradation and the compatibility issue of the bipolar transistor in traditional band gap reference are on the rise; 2, when supply voltage is lower than band gap voltage value (1.26V), the band-gap reference source circuit of conventional voltage pattern is difficult to be suitable for.In view of the above problems, a kind of subthreshold MOSFET band-gap reference source structure is proposed and has obtained broad research by people.For example, Xia Xiaojuan, Xie Liang and Sun Weifeng, " A CMOS Voltage Reference Based on V _GSAnd Δ V _GSIn the Weak InversionRegion; " Chinese Journal of Semiconductors, vol.29 (8), pp.1523-1528,2008. because MOSFET is similar at the transport property and the bipolar transistor of sub-threshold region, said structure adopts subthreshold MOSFET to replace bipolar transistor, greatly reduces circuit complexity and power consumption.Simultaneously, subthreshold MOSFET band-gap reference source can adopt current-mode, realizes low benchmark output voltage arbitrarily, and is not subjected to the restriction of band gap voltage.In addition, the same with traditional band gap reference, the output voltage of subthreshold MOSFET band-gap reference source can be realized good temperature coefficient.

But, because influenced by the technology fluctuation bigger for the parameters such as threshold voltage of MOSFET in the subthreshold MOSFET structure, so the benchmark output voltage values exists than large deviation (maximum deviation reach ± 13.1%) under the different process angle, is difficult to be applicable to a lot of occasions higher to the circuit accuracy requirement.

Summary of the invention

The technical problem to be solved in the present invention is, a kind of subthreshold MOSFET band-gap reference source of anti-technology fluctuation is proposed, it is bigger influenced by process deviation with the output voltage of the subthreshold MOSFET band-gap reference source that overcomes prior art, is difficult to be applicable to much the deficiencies to the higher occasion of circuit accuracy requirement.

Subthreshold MOSFET band-gap reference source of the present invention is taked following technical scheme, and it is made up of start-up circuit, positive temperature coefficient (PTC) current generating circuit, reference voltage generating circuit that negative temperature parameter current of the present invention produces circuit and prior art.Whole reference voltage source was in the conducting duty constantly after start-up circuit guaranteed to power on, the positive temperature coefficient (PTC) current generating circuit is used to produce a current branch that is directly proportional with absolute temperature, negative temperature parameter current produces circuit and is used to produce a current branch that is inversely proportional to absolute temperature, above-mentioned two branch currents converge in reference voltage generating circuit and the Temperature Influence of cancelling out each other (being current-mode), finally produce the reference voltage of a zero-temperature coefficient by resistance.Negative temperature parameter current wherein of the present invention produces circuit and has adopted the bulk potential modulation technique, and it comprises a NMOSFET who is used to monitor of prior art, a biasing resistor, two current mirrors and a limit control capacittance, it is characterized in that it also comprises:

The NMOSFET that bulk potential is adjustable is operated in sub-threshold region, is used to produce negative temperature coefficient voltage;

A modulation voltage generator is used to produce modulation voltage.

The body end of the described NMOSFET that is used to produce negative temperature coefficient voltage is independent from substrate, links to each other with the output terminal of described modulation voltage generator.

Described modulation voltage generator is made up of a rheostat, an operational amplifier and two filter capacitors, wherein rheostat is used to change the output voltage of modulation voltage generator, operational amplifier is used for the voltage buffering, and two filter capacitors are used for noise and other interference that filtering circuit is introduced.

The modulation voltage of modulation voltage generator output is inserted the body end of subthreshold value NMOSFET (being used to produce negative temperature coefficient voltage), can change the parameters such as threshold voltage of this NMOSFET, and then change the negative temperature coefficient voltage of its generation and the negative temperature parameter current value that the place module produces thereof, finally reach the purpose of the output reference voltage that changes band gap reference.In the practical application, can be according to the output reference voltage deviation situation that causes owing to the technology fluctuation, adjust the rheostat in the modulation voltage generator pointedly, produce suitable modulation voltage, reduce the adverse effect of technology fluctuation greatly the output reference voltage of subthreshold MOSFET band-gap reference source.

Advantage of the present invention and good effect: by modulation voltage generator output voltage to the subthreshold value NMOSFET bulk potential modulating action of (being used to produce negative temperature coefficient voltage), make that finally the output reference voltage of subthreshold MOSFET band-gap reference source is more consistent under the situation of different process angle, thereby avoided the adverse effect of process deviation, greatly improved the stability and the robustness of circuit in the situation of not obvious increase circuit complexity.

Description of drawings

Fig. 1 is the subthreshold MOSFET band-gap reference source circuit diagram of prior art;

Fig. 2 varies with temperature curve map for the reference voltage of prior art band gap reference under the different process angle;

Fig. 3 is subthreshold MOSFET band-gap reference source of the present invention (not comprising a modulation voltage generator) circuit diagram;

Fig. 4 is modulation voltage generator circuit figure of the present invention;

Fig. 5 varies with temperature curve map for the reference voltage of band gap reference of the present invention under the different process angle.

Embodiment

Embodiments of the invention:

The subthreshold MOSFET band-gap reference source circuit diagram of prior art as shown in Figure 1, it produces circuit 13 by start-up circuit 11, positive temperature coefficient (PTC) current generating circuit 12, negative temperature parameter current and reference voltage generating circuit 14 is formed.

Start-up circuit 11 is made up of PMOSFET MP1, MP2 and NMOSFET MN1, and whole band gap reference is in the conducting duty constantly after being used for guaranteeing to power on.If circuit enters zero current condition, the grid end of MP1, MP2 and MN1 all is in high level, the phase inverter that this moment, MP1 and MN1 formed is pulled down to low level by force with MP1 drain terminal (MP2 grid end), the MP2 conducting is also injected positive temperature coefficient (PTC) current generating circuit 12 with electric current, and whole band gap reference is opened immediately again.After the unlatching, MP3 grid terminal potential descends, the MP1 conducting, and MP2 ends, and can ignore the influence of start-up circuit 11 like this during the band gap reference operate as normal.

Positive temperature coefficient (PTC) current generating circuit 12 is by PMOSFET MP3, MP4, and NMOSFET MN2, MN3 and resistance R 1 are formed, and wherein MP3, MP4 constitute current-mirror structure, and MN2, MN3 are operated in sub-threshold region, its transport property (I _D-V _GS) similar with bipolar transistor, therefore can substitute the bipolar transistor in traditional band gap reference, its transport property (I _D-V _GS) satisfy relational expression (1):

$I_D=I_{\mathrm{DO}}\mathrm{Sexp}\left(\frac{V_{\mathrm{GS}}-\left|V_{\mathrm{th}}\right|}{n{V}_T}\right)---\left(1\right)$

V wherein _GS, V _ThWith S be respectively gate source voltage, threshold voltage and the breadth length ratio of MOSFET, V _T=kT/q is a thermal voltage, and n is a slope factor, I _D0Be V _GS=V _Th, the leakage current during S=1.Can derive R1 according to formula (1) and go up electric current I _R1(be the output current I of positive temperature coefficient (PTC) current generating circuit 12 _PTAT) be:

$I_{\mathrm{PTAT}}=I_{R1}=\frac{V_{\mathrm{GSN}2}-V_{\mathrm{GSN}3}}{R1}\≅n\frac{\mathrm{kT}}{\mathrm{qR}1}\ln \left(\frac{S_{P3}{S}_{N3}}{S_{P4}{S}_{N2}}\right)---\left(2\right)$

V wherein _GSN2, V _GSN3Be respectively the gate source voltage of MN2, MN3, S _P3, S _P4, S _N2And S _N3It is respectively the breadth length ratio of MP3, MP4, MN2 and MN3.By formula (2) as can be known, the output current I of positive temperature coefficient (PTC) current generating circuit 12 _PTATBe directly proportional with temperature.

Negative temperature parameter current produces circuit 13 by PMOSFET MP5, MP6, MP7, NMOSFETMN4, MN5, and biasing resistor R2 and limit control capacittance C1 form.Wherein MP3, MP4 constitute one group of current-mirror structure in MP5 and the positive temperature coefficient (PTC) current generating circuit 12, and MP6, MP7 constitute another group current-mirror structure, and MN5 is used for monitoring (detailed down), and MN4 is operated in sub-threshold region, its transport property (I _D-V _GS) satisfy formula (1), can derive the gate source voltage V of MN4 thus _GSN4For:

$V_{\mathrm{GSN}4}\≅V_{\mathrm{th}}+n\frac{\mathrm{kT}}{q}\ln \left(\frac{I_D}{I_{D0}{S}_{N4}}\right)---\left(3\right)$

V wherein _GSN4Be the gate source voltage of MN4, S _N4Breadth length ratio for MN4.Because MOSFET I when sub-threshold region _DCertainly less than I _D0S _N4So, the gate source voltage V of MN4 _GSN4Reduce with the temperature increase, negative temperature parameter current produces the output current I of circuit 13 _CTATBe inversely proportional to temperature, see formula (4):

$I_{\mathrm{CTAT}}=\frac{V_{\mathrm{GSN}4}{S}_{P7}}{R2\·S_{P6}}---\left(4\right)$

S wherein _P6, S _P7It is respectively the breadth length ratio of MP6 and MP7.In addition, negative temperature parameter current produces and has a negative feedback in the circuit 13: because the leakage current on the MN4 is provided by the current mirror that MP3, MP4 and MP5 form, current value ratio is more fixing, so MN5 can be by the voltage on the grid terminal potential supervision biasing resistor R2, in case make a mistake, MN5 will adjust electric current and voltage on the R2 by the current mirror that MP6, MP7 form.Limit control capacittance C1 is used to regulate the dominant pole on the feedback control loop.

Reference voltage generating circuit 14 is by PMOSFET MP8, MP9, and resistance R 3 and capacitor C 2 are formed.The output current I of positive temperature coefficient (PTC) current generating circuit 12 _PTATOutput current I with negative temperature parameter current generation circuit 13 _CTATBe mirrored in the reference voltage generating circuit 14 by MP8 and MP9 respectively, the Temperature Influence of cancelling out each other, and, see formula (5) by the final reference voltage V ref of resistance R 3 generations

$V_{\mathrm{ref}}=R3[\frac{n{V}_T}{R1}\ln \left(\frac{S_{P3}{S}_{N3}}{S_{P4}{S}_{N2}}\right)+\frac{V_{\mathrm{GSN}4}{S}_{P7}}{R2\·S_{P6}}]---\left(5\right)$

By formula (5) as can be known, by the reasonable ratio of adjusting R1, R2 and R3, finally can obtain a reference voltage V ref who approaches zero-temperature coefficient.Capacitor C 2 is used for the influence of filter away high frequency noise to reference voltage V ref.

Under 0.13 μ m CMOS mixed signal technology, supply voltage Vdd=1.2V, the reference voltage of prior art band gap reference under the different process angle varies with temperature curve map as shown in Figure 2.As shown in Figure 2, under each process corner (ss, tt and ff), reference voltage V ref all possesses temperature coefficient preferably, and temperature coefficient TC is respectively 30.38ppm, 31.35ppm and 44.33ppm.But the reference voltage value under the different process angle differs approaching ± 100mV, deviation reaches ± and 13.1%, be difficult to be applicable to a lot of occasions higher to the circuit accuracy requirement.

Circuit diagram as shown in Figure 3 for subthreshold MOSFET band-gap reference source of the present invention (not comprising the modulation voltage generator), wherein 11,12 and 14 of start-up circuit 31, positive temperature coefficient (PTC) current generating circuit 32 and reference voltage generating circuit 34 and prior art is identical, the innovation part is that negative temperature parameter current produces in the circuit 33, the body end of subthreshold value NMOSFET MN4 (being used to produce negative temperature coefficient voltage) is independent from substrate, be used for the bulk potential modulation, modulation voltage is defined as Vadjust, and the output terminal of the modulation voltage generator that increases newly with the present invention links to each other.

Modulation voltage generator circuit figure of the present invention as shown in Figure 4, it is made up of rheostat 41, operational amplifier 42 and filter capacitor C3, C4.Wherein rheostat 41 makes the modulation electric pressure energy of modulation voltage generator output change in 0～Vdd scope, but the load capacity of operational amplifier 42 enhanced modulation voltage generators, guarantee the accuracy of modulation voltage Vadjust, filter capacitor C3, C4 are used for noise and other interference that filtering circuit is introduced, wherein consider the capacitive load effect of operational amplifier 42, filter capacitor C4 value is unsuitable excessive, generally at hundreds of fF between several nF, and C3 value is generally at hundreds of nF extremely between a few μ F.

We know, the threshold voltage V of MOSFET _ThAnd exist relation between the bulk potential suc as formula (6)

$V_{\mathrm{th}}=V_{\mathrm{th}0}+\mathrm{\γ}(\sqrt{2\left|{\mathrm{\φ}}_F\right|+v_{\mathrm{SB}}}-\sqrt{2\left|{\mathrm{\φ}}_F\right|})---\left(6\right)$

V wherein _SBBe the source bulk voltage of MOSFET, V _Th0Be v _SB=0 o'clock threshold voltage, γ are body-effect coefficient, φ _FIt is Fermi potential.By following formula as can be known, (adjust v by the bulk potential modulation _SB) can change the threshold voltage of MOSFET.

Therefore, with the body end of modulation voltage Vadjust access subthreshold value NMOSFET MN4, can change the threshold voltage of MN4 effectively, by formula (3)～(5) as can be known, the MN4 variations in threshold voltage will cause MN4 gate source voltage V _GSN4Variation, and then change the reference voltage V ref of band gap reference output.Utilize this characteristic, we can be by adjusting the rheostat 41 in the modulation voltage generator, produce suitable modulation voltage Vadjust and compensate the MN4 variations in threshold voltage that causes owing to the technology fluctuation, and then reduce the adverse effect of technology fluctuation greatly the reference voltage V ref of subthreshold MOSFET band-gap reference source output.

The reference voltage of band gap reference of the present invention under the different process angle varies with temperature curve map as shown in Figure 5.Because the introducing of bulk potential modulation technique, the reference voltage value under the different process angle only differ be ± 25mV, deviation is ± 3.2%, and it is remarkable to improve effect.Temperature coefficient TC under ff and ss process corner is slightly poorer than prior art for band gap reference of the present invention, reason is MN2 and the symmetry of the MN3 to some extent variation of MN4 in bulk potential modulation back and positive temperature coefficient (PTC) current generating circuit 12, but the index temperature coefficient of band gap reference of the present invention stands good in most high-precision circuit occasions.

In sum, be preferred embodiment of the present invention only, be not to be used for limiting practical range of the present invention, promptly all equivalences of doing according to the content of the present patent application claim change and modify, and all should be technology category of the present invention.

Claims (4)

1. subthreshold MOSFET band-gap reference source, it comprises

Start-up circuit (31), the whole reference source in back that guarantees to power on is in the conducting duty constantly;

Positive temperature coefficient (PTC) current generating circuit (32) is used to produce a current branch that is directly proportional with absolute temperature;

Negative temperature parameter current produces circuit (33), is used to produce a current branch that is inversely proportional to absolute temperature;

Reference voltage generating circuit (34) converges above-mentioned two branch currents and the Temperature Influence of cancelling out each other, and finally produces the reference voltage of a zero-temperature coefficient;

It is characterized in that: described negative temperature parameter current produces circuit (33) and has adopted the bulk potential modulation technique, is used for anti-technology fluctuation.

2. subthreshold MOSFET band-gap reference source according to claim 1 is characterized in that: described negative temperature parameter current produces circuit (33) and comprises

A subthreshold value NMOSFET (MN6), bulk potential is adjustable, is used to produce negative temperature coefficient voltage;

A modulation voltage generator is used to produce modulation voltage;

It also comprises a NMOSFET who is used to monitor (MN5), a biasing resistor, two current mirrors and a limit control capacittance.

3. subthreshold MOSFET band-gap reference source according to claim 1, it is characterized in that: described negative temperature parameter current produces in the circuit, the body end of NMOSFET that is used to produce negative temperature coefficient voltage is independent from substrate, links to each other with the output terminal of described modulation voltage generator.

4. subthreshold MOSFET band-gap reference source according to claim 1 is characterized in that: described negative temperature parameter current produces in the circuit, and the modulation voltage generator comprises

A rheostat (41) is used to change the output voltage of modulation voltage generator;

An operational amplifier (42) is used for the voltage buffering;

Two filter capacitors are used for noise and other interference that filtering circuit is introduced.

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