CN100403632C - Fast restoring low voltage drop linear voltage stabilizer - Google Patents

Abstract

The present invention discloses a fast return voltage stabilizer for the drop linear of low voltage, which utilizes the size of output current detected by a current detection circuit and compares the output current with reference current to dynamically regulate the bias current of a second stage amplifier. When the second stage amplifier outputs current, the damping factor zeta of a system is still bigger than 1 and maintains stable. Thereby, when the output current suddenly changes, output voltage can be quickly stored stably.

Description

Quick low-voltage-drop linear voltage regulator of replying

Technical field

The present invention relates to a kind of low-voltage-drop linear voltage regulator (low drop-out linearregulator; LDO), when particularly a kind of output current has bigger variation suddenly, can be returned to the low-voltage-drop linear voltage regulator of burning voltage output fast.

Background technology

When the ripe gradually development in communications market, the application of relevant IC is constantly ripe especially.Yet along with development such as the portability product of mobile phone etc., the length service time additional important especially of battery.How improving the power of battery and keeping its certain stability is a problem that quite has challenge.Low-voltage-drop linear voltage regulator (low drop-out linearregulator is called for short LDO) because the raising of its conversion efficiency adds its small size, low noise characteristic, becomes the main flow of small-power step-down and voltage stabilizing circuit in recent years.On various electronic product of being correlated with, all used in large quantities by the portable system and the communication of battery power supply.

In existing product (method), in order to make low-voltage-drop linear voltage regulator more accurate, generally speaking can adopt the operational amplifier (operational amplifier) of three grades of series systems to increase its gain, yet but can therefore cause unsettled situation.So constantly the someone proposes frequency compensation method miscellaneous and reaches the stable of system.At the beginning, the someone proposes to utilize the outer electric capacity that strengthens to reduce the dominant pole position and increase the phase place limit.But can there be following shortcoming like this:

Because the dominant pole of this type of circuit falls within output point, therefore need come systems stabilisation, yet therefore be not easy this electric capacity is made in chip internal than heavy load electric capacity, can increase the difficulty in the system combination.

Generally speaking, we wish that bigger system gain improves the precision of system, yet improve the stability that gain can reduce system relatively, therefore can cause the choice between precision and the stability.

The size of output current can be subject to the stability of system.Because output current is big more, representing load resistance more little, the therefore relative dominant pole that is positioned at output point is also big more, therefore can make the stability of system poor more.

Because the non-dominant pole of this circuit is positioned at the output point (generally speaking being high impedance) of operational amplifier, the therefore relative first non-dominant pole (first non-dominant pole) is lower, thereby has reduced the frequency range of system, also makes its transient response variation.

Therefore, in order to improve above shortcoming, constantly the someone has proposed frequency compensation method miscellaneous, as: nido is miller-compensated, damping coefficient ζ controls etc.Yet these methods all need two building-out capacitors, and therefore comparatively speaking, the chip area of its use is bigger than simple miller-compensated method again, so the someone had proposed to utilize the single miller-compensated of gain amplification afterwards, see also shown in Figure 1.Though the method has successfully solved above-mentioned problem, its damping coefficient ζ is subjected to the influence of output current size and slows down the stable speed of its output voltage V out.

See also shown in Figure 2ly, be small-signal model shown in Figure 1, wherein gm1, gm2, gmp are respectively the conduction of first, second and output stage, go1, go2, gL are the output conductance of the first order, the second level and output stage, and Cp1, Cg are respectively second and the input parasitic capacitance of output stage.Cout is a load capacitance, and Re is the dead resistance of load capacitance, and Cm1, Rm are building-out capacitor and compensating resistance.A _DcDC current gain for system.ζ is a damping coefficient.Can derive to such an extent that its system's transfer equation formula is as follows by the small-signal model (small signal model) of Fig. 2:

$\mathrm{Av}\left(s\right)=\frac{A_{\mathrm{dc}}(1+{\mathrm{SC}}_{\mathrm{out}}{R}_e)[1+{\mathrm{SC}}_{m1}(R_m-\frac{g_{o2}}{g_{m2}{g}_{\mathrm{mp}}})-S^2\frac{C_{m1}{C}_g}{g_{m2}{g}_{\mathrm{mp}}}]}{(1+\frac{S}{P_{-3\mathrm{db}}})(1+{\mathrm{SC}}_{\mathrm{out}}(R_e+\frac{g_{o2}}{g_{m2}{g}_{\mathrm{mp}}}){+S}^2\frac{C_g{C}_{\mathrm{out}}}{g_{m2}{g}_{\mathrm{mp}}})}\·\·\·\·\left(1\right)$

Wherein $A_{\mathrm{dc}}=\frac{g_{m1}{g}_{m2}{g}_{\mathrm{mp}}}{g_{o1}{g}_{o2}{g}_L},$ $P_{-3\mathrm{db}}=\frac{C_{m1}{g}_{m2}{g}_{\mathrm{mp}}}{g_{o1}{g}_{o2}{g}_L}.$

$\mathrm{\ξ}=\frac{1}{2}{C}_{\mathrm{out}}(R_e+\frac{g_{o2}}{g_{m2}{g}_{\mathrm{mp}}})\sqrt{\frac{g_{m2}{g}_{\mathrm{mp}}}{C_g{C}_{\mathrm{out}}}}$

$(\mathrm{<figure-callout\; id="2"\; label="gm"\; filenames="C20051006462400121.png"\; state="\{\{state\}\}">gm</figure-callout>}2=\frac{I_{b2}}{V_{\mathrm{gs}2}-{\mathrm{<figure-callout\; id="2"\; label="V\; th"\; filenames="C20051006462400121.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{th}}},\mathrm{go}2=\mathrm{\&lambda;Ib}2)$

$\begin{array}{cc}\mathrm{\&alpha;}& \sqrt{\frac{I_{b2}}{g_{\mathrm{mp}}}}\end{array}\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\left(3\right)$

In order to reduce required cost, existing market is inclined to use more cheap electric capacity such as ceramic condenser as load capacitance.Yet the dead resistance of ceramic condenser itself is less, therefore by (2) formula can simplify (3) formula.

Can learn damping coefficient ζ and output stage conduction (g by (3) formula _Mp) be inversely proportional to and with the bias current (I of second level amplifier _B2) be directly proportional, because when output current becomes greatly (during for example by 0.1mA-＞150mA), output stage conduction (gmp) also and then becomes big (about 30 times), therefore can make damping coefficient ζ diminish and less than 1 (even can much smaller than 1), and make frequency response near unit gain frequency, have surging, so that when output current changes suddenly, can produce Lian Boer in the transient response of output voltage V out and slow down its stable speed, thereby the low-voltage-drop linear voltage regulator of a fast and stable can't be provided.

Summary of the invention

Main purpose of the present invention is dynamically to adjust the bias current of second level amplifier, compensates the influence of output current variation to damping coefficient ζ, with the surging of eliminating frequency response and the stabilized speed of accelerating output voltage.

The present invention is a kind of low-voltage-drop linear voltage regulator of quick answer, and it has the low-voltage-drop linear voltage regulator circuit that single miller-compensated electric capacity is amplified in gain, and this low-voltage-drop linear voltage regulator circuit has a second level amplifier (2 ^NdStage amplifier) and have an output current and use for a load, it comprises that a current-sensing circuit, a comparison circuit, a control element and add volt circuit, this current-sensing circuit is used to detect the size of this output current of this compensating circuit, to export a corresponding relatively electric current; This comparison circuit is imported this a comparison electric current and a fixing reference current, makes size relatively and produce a comparison signal to utilize this comparison circuit; This control element is to be controlled by this comparison signal, and exports a control signal; This adds volt circuit, and in order to change the bias current of this second level amplifier, this adds this control signal that volt circuit receives this control element, whether changes the bias current of this second level amplifier with decision; Compare electric current greater than this reference current when this in view of the above, this comparison circuit is exported this comparison signal and is controlled this and add the bias current that volt circuit increases this second level amplifier, offset output current according to this and change the influence of damping coefficient ζ reducing company's ripple of output voltage in the transient response, and accelerate its stabilized speed.

Description of drawings

Fig. 1 is existing low-voltage-drop linear voltage regulator.

Fig. 2 is the small-signal model of Fig. 1.

Fig. 3 is a system circuit diagram of the present invention.

Fig. 4 is the frequency response chart of the present invention when not compensating.

Fig. 5 is the transient response figure of the present invention when not compensating.

Fig. 6 is the frequency response chart after the present invention compensates.

Fig. 7 is the transient response figure after the present invention compensates.

Embodiment

Relevant detailed content of the present invention and technical descriptioon, existing accompanying drawings is as follows:

See also shown in Figure 3, it is a system circuit diagram of the present invention, it comprises that one has the low-voltage-drop linear voltage regulator circuit 10 that single miller-compensated electric capacity (Miller capacitor) is amplified in gain, it utilizes the required driving voltage of high levle supply voltage Vdd supply, and this low-voltage-drop linear voltage regulator circuit 10 has a second level amplifier 101 and has an output current I ₁₀Use for a load, it utilizes current mirror (current mirror) principle to adopt two transistor MP, MPR to form a current-sensing circuit 20, and recycling amplifier 30 forms a negative feedback (feedback) mechanism, removes to detect accurately the output current I of low-voltage-drop linear voltage regulator circuit 10 ₁₀, and export a corresponding relatively electric current I ₂₀, and load and consumption in order to reduce circuit, this is electric current I relatively ₂₀Sizes values can dwindle by multiple, as allow I ₂₀=I ₁₀/ K; Wherein K is that the characteristic of transistor MP, MPR determines.

This is electric current I relatively ₂₀With a fixing reference current I _Ref, utilize a comparison circuit 40 to make comparisons, to export a comparison signal, this reference current I _RefBe that two high levles supply voltage Vdd, Vb and a transistor MI produce, this comparison circuit 40 can be made of 1 current mirror 41 than 1NMOS, and it imports this comparison electric current I respectively ₂₀With this reference current I _Ref, and having a high resistance point Vr, the two ends of this high resistance point Vr are respectively this reference current I _RefCompare electric current I with 1 current mirror 41 according to this than 1NMOS ₂₀The electric current I that equates that produces ₄₀, change by the electric current of measuring this high resistance point Vr, can make current ratio, and produce a comparison signal.

This comparison signal is used to be input to a control element 50 to produce a control signal, and this control element 50 can utilize reverser invn, the invp of two series connection to constitute, and be connected with this high resistance point Vr, thereby change this comparison signal that is produced by the electric current of high resistance point Vr, promptly produce 0,1 control signal of one (invn, invp) via reverser invn, invp (Inverter) of these two series connection.

This control signal is used for control and adds volt circuit 60, and add the bias current that volt circuit 60 is used to change this second level amplifier 101, this adds volt circuit 60 and can be made of first couple of transistor MSP, MSN and second couple of transistor M24a, M22a, whether increases the bias current of second level amplifier 101 with the conducting that utilizes this control signal control first couple of transistor MSP, MSN.

The present invention must determine this reference current I earlier before running _RefSizes values, this reference current I _RefThe optimal design value and the damping coefficient ζ of system less than the output current I that was had in 1 o'clock ₁₀Relevant, if output current I ₁₀Sizes values when being A, the damping coefficient ζ of its system promptly can be less than 1, then this reference current I _RefNumerical value can be made as A/K.

The present invention can be divided into two states when running, at first as output current I ₁₀When exporting with underloading, the damping coefficient ζ of system is greater than 1 at this moment, and this is electric current I relatively ₂₀(=I ₁₀/ K) less than reference current I _RefThe control signal of the reverser of 50 liang of series connection of this control element this moment is (invn:0, invp:1), allow the switch of this transistor MSP, MSN close and be open circuit, so the time second level amplifier 101 bias current do not become big, the damping coefficient ζ of right system at this moment is still greater than 1, it does not need compensation, can allow output current I ₁₀Output voltage V out reach stable fast.

As output current I ₁₀Change when exporting its output current I with heavy duty ₁₀Become big, this moment, the damping coefficient ζ of system began to diminish output current I ₁₀Output voltage V out begin to have unsettled ripples to produce; Yet when comparing electric current I ₂₀Greater than reference current I _RefMoment, the control signal of reverser invn, the invp of 50 liang of series connection of this control element this moment changes (invn:1, invp:0) into, and allow transistor MSP, MSN switch opens and strengthened the bias current of second level amplifier 101, again because damping coefficient ζ is directly proportional with the bias current of second level amplifier 101, so the present invention can compensate output current I by strengthening the bias current of second level amplifier 101 ₁₀To the influence of damping coefficient ζ, allow damping coefficient ζ can keep suitable value (greater than 1).Therefore as output current I ₁₀When being converted to heavy duty (as 150mA) by underloading (as 0.1mA), its output current I ₁₀Output voltage V out also can reach stable status fast.

Please consult Fig. 4 and shown in Figure 5 again, it is respectively the frequency response chart and the transient response figure of this low-voltage-drop linear voltage regulator circuit 10 gained when not compensating.By shown in Figure 4, obviously visible as output current I ₁₀Change when exporting with heavy duty, frequency response chart has surging near unit gain frequency (unity gain frequency), also therefore have the generation of many ripples on the transient response figure of Fig. 5, so that need 34 microseconds consuming time the stabilization time of its output voltage V out.

Please consult Fig. 6 and shown in Figure 7 again, be respectively frequency response (frequency response) figure and transient response (transient response) figure of these low-voltage-drop linear voltage regulator circuit 10 compensation back gained.As seen from Figure 6, near unit gain frequency and the generation of non-surge, also therefore among Fig. 7 as seen, the ripple minimizing in the transient response thereby reached stable (about 8 microseconds) fast; Therefore the present invention is at output current I ₁₀Change when exporting with heavy duty, it still can allow output current I fast ₁₀Output voltage V out return back to stable status.

The above is the preferred embodiments of the present invention only, is not limited to the present invention, and for a person skilled in the art, the present invention can have various changes and variation.Within the spirit and principles in the present invention all, any modification of being done, be equal to replacement, improvement etc., all should be included within the claim scope of the present invention.

Claims (7)

1. low-voltage-drop linear voltage regulator of replying fast, it has the low-voltage-drop linear voltage regulator circuit (10) that single miller-compensated electric capacity is amplified in gain, and described low-voltage-drop linear voltage regulator circuit (10) has a second level amplifier (101) and has an output current (I ₁₀) use for a load, it is characterized in that comprising:

One current-sensing circuit (20), described current-sensing circuit (20) are used to detect the described output current (I of described low-voltage-drop linear voltage regulator circuit (10) ₁₀) size, to export an electric current (I relatively ₂₀);

One comparison circuit (40) is imported described relatively electric current (I ₂₀) with a fixing reference current (Iref), make size relatively and produce a comparison signal to utilize described comparison circuit (40);

One control element (50), described control element (50) is controlled by described comparison signal, and exports a control signal;

One adds volt circuit (60), in order to changing the bias current of described second level amplifier (101), describedly adds the described control signal that volt circuit (60) receives described control element (50), whether changes the bias current of described second level amplifier (101) with decision; In view of the above as described relatively electric current (I ₂₀) during greater than described reference current (Iref), the described volt circuit (60) that adds of the described comparison signal control of described comparison circuit (40) output is to increase the bias current of described second level amplifier (101).

2. low-voltage-drop linear voltage regulator according to claim 1 is characterized in that described current-sensing circuit (20) is made of current mirroring circuit.

3. low-voltage-drop linear voltage regulator according to claim 2 is characterized in that also having an amplifier (30), and described amplifier (30) forms a negative feedback mechanism with described current-sensing circuit (20).

4. low-voltage-drop linear voltage regulator according to claim 1 is characterized in that described comparison circuit (40) is made of 1 current mirror than 1NMOS (41), and described comparison circuit (40) is imported described relatively electric current (I respectively ₂₀) with described reference current (Iref), and described comparison circuit (40) has a high resistance point (Vr), the two ends of described high resistance point (Vr) are respectively described reference current (Iref) and 1 current mirror than 1NMOS (41) according to described relatively electric current (I ₂₀) electric current (I that produced ₄₀), change by the electric current of measuring described high resistance point (Vr), can make current ratio.

5. low-voltage-drop linear voltage regulator according to claim 1 is characterized in that described control element (50) is two reversers (invn, an invp) serial connection and constituting, and allows described control signal have 0,1 signal output of two reversers (invn, invp).

6. low-voltage-drop linear voltage regulator according to claim 1, it is characterized in that the described volt circuit (60) that adds is made of first pair of transistor (MSP, MSN) and second pair of transistor (M24a, M22a), whether its conducting that utilizes described control signal to control described first pair of transistor (MSP, MSN) increases the bias current of described second level amplifier (101).

7. low-voltage-drop linear voltage regulator according to claim 1 is characterized in that described relatively electric current (I ₂₀) sizes values be described output current (I ₁₀) multiple dwindle.

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