CN103645771A - Current mirror - Google Patents

Abstract

The invention relates to electronic circuit technology, in particular to a current mirror with relatively large drive capability. A current mirror of the present invention includes a first NMOS transistor M1 and a second NMOS transistor M2, and is characterized in that it also includes a first resistor R1, a second resistor R2 and a bias current source I _bias , the first resistor R1 One end of the second resistor R2 is connected to the first input end of the current mirror, and the drain of the second NMOS transistor M2 is connected to the second input end of the current mirror; the other end of the first resistor R1 is connected to the first NMOS transistor M1 The drain of the second resistor R2 is connected to the gate, and the other end of the second resistor R2 is connected to the gate of the second NMOS transistor M2 and the positive input end of the bias current source I _bias ; the source of the first NMOS transistor M1, the second NMOS transistor M2 The source of the bias current source and the negative electrode of the _bias current source Ibias are grounded. The beneficial effect of the invention is that, compared with the common current mirror under the same static current condition, a larger dynamic output current can be obtained, and the driving ability is stronger. The invention is particularly applicable to current mirrors.

Description

A kind of current mirror

Technical field

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

Background technology

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

As shown in Figure 1, metal-oxide-semiconductor MP1 is always in state of saturation, according to the relation of saturated metal-oxide-semiconductor drain-source current and gate source voltage for the simplest current mirror

(wherein,

μ is electronics or hole mobility; C _oxthe gate oxide electric capacity of representation unit area;

breadth length ratio for metal-oxide-semiconductor; V _gsfor gate source voltage; V _thfor threshold voltage) can obtain: if the gate source voltage of two identical metal-oxide-semiconductors (having identical breadth length ratio and threshold voltage) is equal, its drain-source current also equates so.If breadth length ratio is different, MP1, the ratio that the electric current flowing through on MP2 pipe is proportional to breadth length ratio is:

$\frac{I_2}{I_1}=\frac{{\mathrm{\&beta;}}_{\mathrm{<figure-callout\; id="2"\; label="MP"\; filenames="HDA0000439807870000011.png,HDA0000439807870000012.png"\; state="\{\{state\}\}">MP</figure-callout>}2}}{{\mathrm{\&beta;}}_{\mathrm{MP}1}}=\frac{{\mathrm{<figure-callout\; id="2"\; label="W"\; filenames="HDA0000439807870000011.png,HDA0000439807870000012.png"\; state="\{\{state\}\}">W</figure-callout>}}_2/L_2}{W_1/L_1}=K$

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.Input current one timing when current mirror, obtain larger output current, needs larger scale factor K.But along with the increase of scale factor K, the quiescent current of current mirror output terminal, by proportional increase thereupon, has increased quiescent dissipation.Therefore, when design OTA, must between quiescent dissipation and driving force, compromise, select suitable current mirror scale factor K.For both requiring little quiescent dissipation, have again the application scenario of large transient response speed (being large output current ability), as be 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, for above-mentioned conventional current mirror, between quiescent dissipation and dynamic driving ability, there is exactly the problem of contradiction, a kind of current mirror with low speed paper tape reader static power disspation, large driving force is proposed.

The present invention solves the problems of the technologies described above adopted technical scheme: a kind of current mirror, comprise a NMOS pipe M1 and the 2nd NMOS pipe M2, and it is characterized in that, also comprise the first resistance R 1, the second resistance R 2 and bias current sources I _bias, one end of described the first resistance R 1 is connected the first input end of current mirror with one end of the second resistance R 2, and the drain electrode of described the 2nd NMOS pipe M2 connects the second input end of current mirror; The other end of the first resistance R 1 is connected with the drain and gate of a NMOS pipe M1, grid and the bias current sources I of the other end of the second resistance R 2 and the 2nd NMOS pipe M2 _biaspositive input terminal connects; Source electrode and the bias current sources I of the source electrode of the one NMOS pipe M1, the 2nd NMOS pipe M2 _biasthe equal ground connection of negative pole.

The technical scheme that the present invention is total, adopt resistance sampling input current, be converted on the gate source voltage that voltage is superimposed upon current mirror output mos pipe, and utilize the square law transport property of metal-oxide-semiconductor itself, make the quadratic term that comprises input current in output current, thereby greatly improved current mirror output current driving force.

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

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 with the OTA of 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 a NMOS pipe M1, the 2nd NMOS pipe M2, the first resistance R 1, the second resistance R 2 and bias current sources I _bias, one end of described the first resistance R 1 is connected the first input end of current mirror with one end of the second resistance R 2, and the drain electrode of described the 2nd NMOS pipe M2 connects the second input end of current mirror; The other end of the first resistance R 1 is connected with the drain and gate of a NMOS pipe M1, grid and the bias current sources I of the other end of the second resistance R 2 and the 2nd NMOS pipe M2 _biaspositive input terminal connects; Source electrode and the bias current sources I of the source electrode of the one NMOS pipe M1, the 2nd NMOS pipe M2 _biasthe equal ground connection of negative pole.

Principle of work of the present invention is:

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

${\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="HDA0000439807870000011.png,HDA0000439807870000012.png"\; state="\{\{state\}\}">V</figure-callout>}}_2=\sqrt{\frac{2I_1}{{\mathrm{\&beta;}}_M}}+V_{\mathrm{th},N}+I_1\&CenterDot;R_1-I_{\mathrm{bias}}\&CenterDot;R_2---\left(1\right)$

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

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

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

$I_2=\frac{{\mathrm{\&beta;}}_{\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="HDA0000439807870000011.png,HDA0000439807870000012.png"\; state="\{\{state\}\}">M</figure-callout>}2}}{{\mathrm{\&beta;}}_{M1}}{I}_1=K\&CenterDot;I_1---\left(3\right)$

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

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

$\begin{array}{c}{I}_2\&ap;\frac{1}{2}{\mathrm{\&beta;}}_{M2}{[\sqrt{\frac{{2I}_1}{{\mathrm{\&beta;}}_{M1}}}+I_1\&CenterDot;R_1]}^2\\ ={\mathrm{\&beta;}}_{M2}[\frac{I_1}{{\mathrm{\&beta;}}_{M1}}+\frac{{(I_1\&CenterDot;R_2)}^2}{2}+\sqrt{\frac{{2I}_1}{{\mathrm{\&beta;}}_{M1}}}\&CenterDot;I_1\&CenterDot;R_1]\\ =K\&CenterDot;I_1+{\mathrm{\&beta;}}_{\mathrm{<figure-callout\; id="2"\; label="M"\; filenames="HDA0000439807870000011.png,HDA0000439807870000012.png"\; state="\{\{state\}\}">M</figure-callout>}2}\&CenterDot;[\frac{{(I_1\&CenterDot;R_1)}^2}{2}+\sqrt{\frac{{2I}_1}{{\mathrm{\&beta;}}_{M1}}}\&CenterDot;I_1\&CenterDot;R_1]\end{array}---\left(4\right)$

By formula (4), can be found out, the quadratic term that output current expression formula contains input current, has increased output current ability, has improved transient response speed.

By formula (3) and formula (4), can be drawn, compare with common current mirror, the present invention adopts resistance sampling input current, be converted on the gate source voltage that voltage is superimposed upon current mirror output mos pipe, and utilize the square law transport property of metal-oxide-semiconductor itself, make the quadratic term that comprises input current in output current, thereby greatly improved current mirror output current driving force.Thereby, this current mirror is had under the quiescent current conditions identical with common current mirror, can obtain larger dynamic output 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 while getting different value, R ₁and R ₂resistance be 0 o'clock, this current mirror is common current mirror.Can find out, resistance is larger, and the quadratic term proportion in output current is larger, and output driving force is stronger; But, at (the input current I of quiescent point place _{1, static}equal the bias current I of 2 times _bias), output quiescent current I _{2, static}equate, power consumption is identical.

Bias current sources I is set _bias(can be the current source of single transistor, can be also cascode current source, by the breadth length ratio of pipe is set, bias current size is set), 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 equate.This instructions is got R ₂, R ₁resistance is that special case describes while equating, can, according to factors such as power consumption and driving forces, select suitable resistance and bias current in actual applications.This current mirror can be used for the occasion of the OTA second level or the large driving force of other needs.

As shown in Figure 5, the second level using 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 respectively to differential pair two output terminals, and passes through M _4Rand M _4Lthe common current mirror forming converts Single-end output to.By V is set _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, comprising a first NMOS transistor M1 and a second NMOS transistor M2, characterized in that it also includes a first resistor R1, a second resistor R2 and a _bias current source Ibias, the first resistor R1 One end and one end of the second resistor R2 are connected to the first input end of the current mirror, and the drain of the second NMOS transistor M2 is connected to the second input end of the current mirror; the other end of the first resistor R1 is connected to the first NMOS transistor M1 The drain is connected to the grid, and the other end of the second resistor R2 is connected to the gate of the second NMOS transistor M2 and the positive input end of the bias current source I _bias ; the source of the first NMOS transistor M1, the second NMOS transistor M2 Both the source and the negative terminal of the bias current source I _bias are connected to ground.

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