CN103645771B - A kind of current mirror - Google Patents

Abstract

The present invention relates to electronic circuit technology, relate to a kind of current mirror with larger driving force specifically.A kind of current mirror of the present invention, comprises the first NMOS tube M1 and the second NMOS tube M2, it is characterized in that, also comprises the first resistance R1, the second resistance R2 and bias current sources I _bias, one end of described first resistance R1 is connected the first input end of current mirror with one end of the second resistance R2, the drain electrode of described second NMOS tube M2 connects the second input end of current mirror; The other end of the first resistance R1 is connected with the drain and gate of the first NMOS tube M1, the other end of the second resistance R2 and the grid of the second NMOS tube M2 and bias current sources I _biaspositive input terminal connects; The source electrode of the first NMOS tube M1, the source electrode of the second NMOS tube M2 and bias current sources I _biasthe equal ground connection of negative pole.Beneficial effect of the present invention is, compared with common current mirror is under identical quiescent current conditions, can obtain larger dynamical output electric current, driving force is stronger.The present invention is particularly useful for current mirror.

Description

A kind of current mirror

Technical field

The present invention relates to electronic circuit technology, relate to a kind of current mirror with larger driving force specifically.

Background technology

Current mirror is the important circuit unit of of mimic channel, may be used for replica current, and it both also as Signal Processing Element, can be widely used in various simulation and radio circuit design as bias unit.

As shown in Figure 1, metal-oxide-semiconductor MP1 is in state of saturation to the simplest current mirror always, according to the relation of saturated metal-oxide-semiconductor drain-source current and gate source voltage (wherein, μ is electronics or hole mobility; C _oxthe gate oxide capacitance of representation unit area; for the breadth length ratio of metal-oxide-semiconductor; V _gsfor gate source voltage; V _thfor threshold voltage) can obtain: if the gate source voltage of the metal-oxide-semiconductor that two are identical (having identical breadth length ratio and threshold voltage) is equal, so its drain-source current is also equal.If breadth length ratio is different, then the ratio that electric current MP1, MP2 pipe flow through is proportional to breadth length ratio is:

$\frac{I_2}{I_1}=\frac{{\mathrm{\β}}_{\mathrm{MP}2}}{{\mathrm{\β}}_{\mathrm{MP}1}}=\frac{W_2/L_2}{W_1/L_1}=K$

The current mirror of cascode structure has the output impedance more much bigger than simple current mirror.As shown in Figure 2 be standard common-source common-gate current mirror, the output impedance of current mirror is:

R _out＝g _MP4r _o4r _o2

But the same with simple current mirror, input and output electric current is proportional to the ratio of breadth length ratio.

At existing OTA(operation transconductance amplifier) in circuit, the second level adopts common current mirror or cascode current mirror as output stage.When input current one timing of current mirror, larger output current be obtained, need larger scale factor K.But along with the increase of scale factor K, the quiescent current of current mirror outputs, by thereupon proportional increase, namely increases quiescent dissipation.Therefore, when designing OTA, must compromise between quiescent dissipation and driving force, selecting suitable current mirror scale factor K.For both requiring little quiescent dissipation, have the application scenario of large transient response speed (namely large output current ability) again, as being applied to LDR(low-dropout regulator) in OTA, existing current mirror cannot satisfy the demands.

Summary of the invention

To be solved by this invention, between quiescent dissipation and dynamic driving ability, there is the problem of contradiction exactly for above-mentioned conventional current mirror, propose a kind of current mirror with low speed paper tape reader static power disspation, large driving force.

The present invention solves the problems of the technologies described above adopted technical scheme: a kind of current mirror, comprises the first NMOS tube M1 and the second NMOS tube M2, it is characterized in that, also comprises the first resistance R1, the second resistance R2 and bias current sources I _bias, one end of described first resistance R1 is connected the first input end of current mirror with one end of the second resistance R2, the drain electrode of described second NMOS tube M2 connects the second input end of current mirror; The other end of the first resistance R1 is connected with the drain and gate of the first NMOS tube M1, the other end of the second resistance R2 and the grid of the second NMOS tube M2 and bias current sources I _biaspositive input terminal connects; The source electrode of the first NMOS tube M1, the source electrode of the second NMOS tube M2 and bias current sources I _biasthe equal ground connection of negative pole.

The technical scheme that the present invention is total, adopt resistance sampling input current, be converted into voltage superposition on the gate source voltage of current mirror output mos pipe, and utilize the square law transport property of metal-oxide-semiconductor itself, make the quadratic term comprising input current in output current, thus substantially increase current mirror output current driving force.

Beneficial effect of the present invention is, compared with common current mirror is under identical quiescent current conditions, can obtain larger dynamical output electric current, driving force is stronger; Under identical driving force requires, lower quiescent dissipation can be reached, be applicable to require little quiescent dissipation, have the application scenario of large transient response speed again.

Accompanying drawing explanation

Fig. 1 is fundamental current mirror structural representation;

Fig. 2 is standard common-source common-gate current mirror structural representation;

Fig. 3 is the structural representation of current mirror of the present invention;

Fig. 4 is the output characteristic curve schematic diagram of current mirror of the present invention;

Fig. 5 is the structural representation of the OTA with current mirror of the present invention.

Embodiment

Below in conjunction with accompanying drawing, describe technical scheme of the present invention in detail:

As shown in Figure 3, current mirror of the present invention, comprises the first NMOS tube M1, the second NMOS tube M2, the first resistance R1, the second resistance R2 and bias current sources I _bias, one end of described first resistance R1 is connected the first input end of current mirror with one end of the second resistance R2, the drain electrode of described second NMOS tube M2 connects the second input end of current mirror; The other end of the first resistance R1 is connected with the drain and gate of the first NMOS tube M1, the other end of the second resistance R2 and the grid of the second NMOS tube M2 and bias current sources I _biaspositive input terminal connects; The source electrode of the first NMOS tube M1, the source electrode of the second NMOS tube M2 and bias current sources I _biasthe equal ground connection of negative pole.

Principle of work of the present invention is:

M ₂the gate voltage V of pipe ₂m can be expressed as ₁the gate source voltage of pipe adds R ₁on pressure drop, then deduct R ₂on pressure drop.Result is as follows:

$V_2=\sqrt{\frac{2I_1}{{\mathrm{\β}}_M}}+V_{\mathrm{th},N}+I_1\·R_1-I_{\mathrm{bias}}\·R_2---\left(1\right)$

Determine gate voltage, substitute into metal-oxide-semiconductor current characteristics equation: in, obtain output current I ₂expression formula, as follows:

$I_2=\frac{1}{2}{\mathrm{\β}}_{M2}{[\sqrt{\frac{{2I}_1}{{\mathrm{\β}}_{M1}}}+I_1\·R_1-I_{\mathrm{bias}}\·R_2]}^2---\left(2\right)$

Select bias current I _biassize, make R ₂, R ₁on quiescent voltage equal, thus make to flow through M ₂and M ₁the quiescent current of pipe is equal.Can find out, now the quiescent current of output terminal is:

$I_2=\frac{{\mathrm{\β}}_{M2}}{{\mathrm{\β}}_{M1}}{I}_1=K\·I_1---\left(3\right)$

Can draw, this current mirror has identical quiescent current with common current mirror.

As input current I ₁time very large, cause resistance R ₁on pressure drop be far longer than R ₂on pressure drop.Formula (3) is reduced to:

$\begin{array}{c}{I}_2\≈\frac{1}{2}{\mathrm{\β}}_{M2}{[\sqrt{\frac{{2I}_1}{{\mathrm{\β}}_{M1}}}+I_1\·R_1]}^2\\ ={\mathrm{\β}}_{M2}[\frac{I_1}{{\mathrm{\β}}_{M1}}+\frac{{(I_1\·R_2)}^2}{2}+\sqrt{\frac{{2I}_1}{{\mathrm{\β}}_{M1}}}\·I_1\·R_1]\\ =K\·I_1+{\mathrm{\β}}_{M2}\·[\frac{{(I_1\·R_1)}^2}{2}+\sqrt{\frac{{2I}_1}{{\mathrm{\β}}_{M1}}}\·I_1\·R_1]\end{array}---\left(4\right)$

As can be seen from formula (4), output current expression formula contains the quadratic term of input current, increases output current ability, improves transient response speed.

Can be drawn by formula (3) and formula (4), compare with common current mirror, the present invention adopts resistance sampling input current, be converted into voltage superposition on the gate source voltage of current mirror output mos pipe, and utilize the square law transport property of metal-oxide-semiconductor itself, make the quadratic term comprising input current in output current, thus substantially increase current mirror output current driving force.Thus make this current mirror have under the quiescent current conditions identical with common current mirror, can obtain larger dynamical output electric current, driving force is stronger.In other words, under identical driving force requires, the present invention can reach lower quiescent dissipation.

Figure 4 shows that resistance R ₁and R ₂the output current characteristic of resistance when getting different value, R ₁and R ₂resistance when being 0, this current mirror is common current mirror.Can find out, resistance is larger, and the quadratic term proportion in output current is larger, exports driving force stronger; But, at quiescent point place (input current I _{1, static}equal the bias current I of 2 times _bias), export quiescent current I _{2, static}equal, power consumption is identical.

Bias current sources I is set _bias(can be the current source of single transistor, also can be cascode current source, arrange bias current size by the breadth length ratio arranging pipe), allows and flows through R ₂electric current I _biaswith flow through R ₁quiescent current I ₁-I _biasbe inversely proportional to resistance R ₂, R ₁resistance, make resistance R ₂, R ₁on static drop equal.R got by this instructions ₂, R ₁be that special case is described when resistance is equal, according to the factor such as power consumption and driving force, suitable resistance and bias current can be selected in actual applications.This current mirror can be used for the OTA second level or other need the occasion of large driving force.

As shown in Figure 5, using the second level of this current mirror as OTA, to improve the driving force of OTA.The input end of two large driving force current mirror Mirror1, Mirror2 is connected on differential pair two output terminal respectively, and passes through M _4Rand M _4Lthe common current mirror of composition converts Single-end output to.By arranging V _b,P, V _b,N, make to flow through R _2L, R _2Ron quiescent current equal differential-pair tail current I _b1/4th.This circuit has the current driving ability larger than common OTA.

Claims (1)

1. a current mirror, comprises the first NMOS tube M1 and the second NMOS tube M2, it is characterized in that, also comprises the first resistance R1, the second resistance R2 and bias current sources I _bias, one end of described first resistance R1 is connected the first input end of current mirror with one end of the second resistance R2, the drain electrode of described second NMOS tube M2 connects the second input end of current mirror; The other end of the first resistance R1 is connected with the drain and gate of the first NMOS tube M1, the other end of the second resistance R2 and the grid of the second NMOS tube M2 and bias current sources I _biaspositive input terminal connects; The source electrode of the first NMOS tube M1, the source electrode of the second NMOS tube M2 and bias current sources I _biasthe equal ground connection of negative pole.