CN1828470A - Circuit for enhancing driving capability of low voltage-difference linear voltage manostat - Google Patents

Abstract

Based on prior art, the circuit also comprises: a switch circuit (307) to control the connection of substrate power of output pipe (103), and a connected switch control circuit (308) to control the switch in (307). Wherein, to low VIN voltage and small grid voltage, it connects the substrate potential to VOUT; or else, it connects the substrate potential to VIN. This invention is also easy to integrate with common CMOS technique.

Description

A kind of circuit that strengthens driving capability of low voltage-difference linear voltage manostat

Technical field

The present invention relates to a kind of Analogous Integrated Electronic Circuits technology, especially refer to a kind of circuit that strengthens driving capability of low voltage-difference linear voltage manostat.

Background technology

LDO (Low Dropout Regulator; low pressure difference linear voltage regulator) is power supply IC (Integratedcircuit; integrated circuit) important branch in; with based on PWM (Pulse Width Modulation; pulse-length modulation); PFM (Pulse Frequency Modulation; the pulse frequency modulation principle) DC-DC (DC-to-dc) converter is compared; it is low that it has a cost; low and the little advantage of quiescent current of noise; simultaneously owing to need not inductance; also can not bring the problem of EMI, in portable product is used, use the power supply of LDO as system through regular meeting.

As shown in Figure 1, a basic LDO is made of efferent duct 103, resistance pressure-dividing network 104, error amplifier 102 and reference voltage 101.The reference voltage generation module is band-gap reference (bandgap) voltage normally, and this module produces a reference voltage that changes with conditions of work such as supply voltage, chip temperatures hardly.Output voltage VO UT samples by resistance R 1, R2 dividing potential drop, and this voltage division signal feeds back to the input end of error amplifier EA (Error Amplifier).Another input end of error amplifier connects reference voltage, the output VG of error amplifier receives a PMOS driving tube MPX with very big breadth length ratio, when the variation when external loading condition or other conditions makes that output voltage VO UT changes, the output VG voltage of error amplifier also can change thereupon, the conducting degree of control PMOS pipe MPX, thus make the voltage of VOUT remain unchanged.Load capacitance CL is used for auxiliary control makes that a such closed loop feedback system keeps stablizing under various application conditions situations, RL be LDO output with equivalent load.

Continuous development along with portable consumer electronic device (for example mobile phone, MP3 player, digital camera or the like) also constantly proposes new requirement to power supply IC.Along with the progress of technology, the technology of .18um .13um live width has progressively become main flow technology, and the needed operating voltage of master chip constantly reduces simultaneously, so just needs LDO can produce lower output voltage, for example: 1.2V, 1.5V, 1.8V or the like.

In portable set, what especially pay close attention to is the conversion efficiency of power supply IC, and for LDO, its efficient depends on the input voltage of LDO and the ratio of output voltage to a great extent.Do not consider the static current consumption of LDO internal work circuit, the efficient of LDO is approximately:

η=VOUT/VIN*100% formula (1)

Can see that for identical VOUT, VIN is low more, the conversion efficiency of LDO is just high more so.But,, under near the VOUT voltage condition, drive the gate source voltage V of big pmos MPX along with the reduction of input voltage VIN _GSBe restricted, be at most VIN, the current driving ability of MPX also reduces thereupon, and this has just limited the driving force of LDO.The conducting electric current of PMOS pipe is

$I_D=\frac{1}{2}{\mathrm{\μ}}_p{C}_{\mathrm{OX}}\frac{W}{L}{(V_{\mathrm{GS}}-V_{\mathrm{TH}})}^2$ Formula (2)

μ in the formula _pBe the mobility of holoe carrier, C _OXBe the gate oxide electric capacity of unit area. Be the breadth length ratio of efferent duct, be the threshold voltage of PMOS pipe.

For this LDO driving stage,, will inevitably run into the not enough problem of driving force along with the decline of input voltage VIN based on CMOS technology.

In order to improve the driving force of output driving tube MPX, in design, can allow MPX that bigger breadth length ratio is arranged, and bigger breadth length ratio needs bigger chip area, can bring the increase of chip cost like this, bigger breadth length ratio is brought bigger stray capacitance simultaneously, and this response speed to LDO has adverse influence again.

The PMOS pipe is a four-terminal device, is respectively, and grid (Gate), source (Source), leakage (Drain) and substrate (Buck), in Fig. 1, the grid of MPX are connected on the output of error amplifier EA, and source end and substrate are received VIN together, and drain terminal is received VOUT.

And under the situation of limited gate source voltage and PMOS pipe MPX size, giving increases a forward bias between source and the substrate, and changing threshold voltage is a highly effective method.Threshold voltage is:

$V_{\mathrm{TH}}=V_{\mathrm{TH}0}+\mathrm{\γ}(\sqrt{\left|2{\mathrm{\Φ}}_F\right|-V_{\mathrm{SB}}}-\sqrt{\left|2{\mathrm{\Φ}}_F\right|})$ Formula (3)

V in the formula _TH0Grid voltage when the electron concentration that is defined as the interface equals the majority carrier density of P type substrate, γ is a body-effect coefficient, | 2 Φ _F| be surperficial transoid gesture.

By formula (2) (3) as can be seen, under identical VGS situation, along with source lining voltage V _SBIncrease, V _THDiminish I _DBecome big.So just improved the driving force of MPX, made that MPX can the bigger electric current of conducting.

In order to increase the LDO driving force, existing solution circuit as shown in Figure 2.

It is a kind of current mirror sampling efferent duct electric current change source lining voltage V that Fig. 2 increases structure (206) newly _SBMethod, diode D is a schottky diode.During the underload low current, V _SBBe approximately 0.Along with the flow through electric current of MPX of load increase increases, the MPS sample rate current increases, V _SBIncrease the V of MPX _THDiminish, make the driving force of MPX get a promotion.

But, in common CMOS technology, generally can not provide such schottky diode, in order to realize above-mentioned circuit structure, need an external schottky diode, be unfavorable for integratedly like this, also increased application cost.

Summary of the invention

The object of the present invention is to provide a kind of circuit that strengthens driving capability of low voltage-difference linear voltage manostat, can not only improve the LDO driving force, improve the conversion efficiency of LDO, and realize easily.

A kind of circuit that strengthens driving capability of low voltage-difference linear voltage manostat provided by the present invention, based on the circuit of forming by efferent duct, error amplifier, reference voltage source, resistance pressure-dividing network and load, it is characterized in that: it also comprises an on-off circuit and the ON-OFF control circuit that is attached thereto, wherein: on-off circuit is used to control the connection of the substrate electric potential of efferent duct; ON-OFF control circuit is used for controlling the conduction status of described on-off circuit switch.

In the circuit of above-mentioned enhancing driving capability of low voltage-difference linear voltage manostat, on-off circuit comprises two metal-oxide-semiconductor MP1, MP2 and a phase inverter INV.

In the circuit of above-mentioned enhancing driving capability of low voltage-difference linear voltage manostat, two metal-oxide-semiconductor MP1, MP2 form not the switch of conducting simultaneously.

In the circuit of above-mentioned enhancing driving capability of low voltage-difference linear voltage manostat, the two switches not mode of conducting simultaneously are: when the first metal-oxide-semiconductor MP1 conducting, the substrate of efferent duct MPX is received input voltage VIN, is normal conditions; When the second metal-oxide-semiconductor MP2 conducting, the substrate electric potential of efferent duct MPX is received output voltage VO UT, produces a VSB voltage this moment.

In the circuit of above-mentioned enhancing driving capability of low voltage-difference linear voltage manostat, ON-OFF control circuit is made of comparer, resistance R 3 and a current source ISR with hysteresis characteristic, the negative terminal of comparer meets output voltage VO UT, the reference potential that produces between positive termination one current source and resistance.

Owing to adopted above-mentioned technical solution, that is, during lower in the VIN voltage ratio, as need to strengthen efferent duct current driving ability, at this moment the substrate electric potential of efferent duct is received VOUT, and higher when the VIN voltage ratio, when the efferent duct driving force is enough, the substrate electric potential of efferent duct is received VIN.By such circuit that dynamically changes the efferent duct underlayer voltage, can strengthen the driving force of LDO when VIN voltage is low greatly, simultaneously, sort circuit is easy to integrated, and being beneficial to common CMOS technology can realize.

Description of drawings

Fig. 1 is the circuit diagram of an existing basic LDO;

Fig. 2 is the circuit diagram after the existing increase LDO driving force;

Fig. 3 is the circuit diagram that the present invention strengthens the LDO driving force.

Embodiment

As shown in Figure 3, the present invention, it is a kind of circuit that strengthens driving capability of low voltage-difference linear voltage manostat, based on the available circuit of being formed by efferent duct 103, error amplifier 102, reference voltage source 101, resistance pressure-dividing network 104 and load 105, it is characterized in that: it also comprises an on-off circuit 307 and the ON-OFF control circuit 308 that is attached thereto, wherein:

On-off circuit 307 comprises two metal-oxide-semiconductor MP1, MP2 and a phase inverter INV, is used to control the connection of the substrate electric potential of efferent duct 103;

ON-OFF control circuit 308 is made of comparer, resistance R 3 and a current source ISR with hysteresis characteristic, the negative terminal of comparer meets output voltage VO UT, the reference potential that produces between positive termination one current source and resistance is used for controlling the conduction status of a certain switch of described on-off circuit 307.

Referring to Fig. 3, utilize MOS switch 307 to control the connection of the substrate electric potential of efferent duct MPX, switch MP1 and MP2 are one group of not switches of conducting simultaneously, when the MP1 conducting, the substrate of MPX is received VIN, is normal conditions; When the MP2 conducting, the substrate electric potential of MPX is received VOUT, produces a VSB voltage this moment.The conduction status of MP1 and MP2 is determined by ON-OFF control circuit (308).ON-OFF control circuit 308 is made of a comparer with hysteresis characteristic, and the negative terminal of comparer meets VOUT, the reference potential positive what resistance of termination one current source produces, and this current potential is:

V+＝VIN-VR3＝VIN-ISR*R3

Current source ISR makes R3 go up the pressure drop that produces about a 300mV.

Work as V _IN-V _R3＞V _OUTThe time, MP1 conducting, V _SB=0.

Work as V _IN-V _R3＜V _OUTThe time, MP2 conducting, V _SB=V _IN-V _OUT

Control the substrate electric potential of MPX dynamically by a such construction of switch, make lower and during near VOUT when the VIN voltage ratio, the substrate electric potential of MPX is received VOUT, the source end of forward bias MPX is to the voltage of substrate, so just equivalence has reduced the threshold voltage of MPX, thereby has strengthened the current driving ability of MPX.And comparer has hysteresis characteristic, makes the switching of underlayer voltage of MPX can frequently not change along with the variation of VIN, VOUT again, has improved the stability of system like this, returns stagnant voltage usually and can be set to 100mV～200mV.

The current driving ability formula of MPX is as follows:

$I_D=\frac{1}{2}{\mathrm{\μ}}_p{C}_{\mathrm{OX}}\frac{W}{L}{(V_{\mathrm{GS}}-V_{\mathrm{TH}0}-\mathrm{\γ}(\sqrt{\left|2{\mathrm{\Φ}}_F\right|-V_{\mathrm{SB}}}-\sqrt{\left|2{\mathrm{\Φ}}_F\right|}))}^2$ Formula (4)

For VIN=1.5V, under a kind of applicable cases of VOUT=1.2V, can calculate and whether adopt the present invention to bring the difference of efferent duct current driving ability:

μ _pC _OXBe 15uA/V ², V _TH0Be 0.9V, γ is 0.5V ^1/2, | 2 Φ _F| be 0.6V, this Several Parameters is the parameter relevant with technology, and the breadth length ratio W/L of MPX is designed to 40000, when VIN voltage is 1.5V, and V _GSMaximal value is 1.5V,

Work as V _SBBe 0 o'clock, I _Dmax=108mA.

Work as V _SBDuring for 0.3V, I _Dmax=152.7mA.

As seen: if do not adopt method of the present invention, the substrate electric potential of MPX fixedly meets VIN, and the maximum drive ability of MPX is 108mA so, and behind the circuit that adopts this patent to propose, driving force can increase to 152.7mA, and driving force has had great improvement.

In sum, the present invention has following advantage:

1. under the lower situation of VIN voltage ratio, significantly improve the LDO driving force.

2. technology realizes can realizing with general CMOS technology easily, need not extra components and parts when using.

Above embodiment is only for the usefulness that the present invention is described, but not limitation of the present invention, person skilled in the relevant technique, under the situation that does not break away from the spirit and scope of the present invention, can also make various conversion or modification, therefore all technical schemes that are equal to also should belong within the category of the present invention, should be limited by each claim.And include within the scope of claim.

Claims (5)

1. circuit that strengthens driving capability of low voltage-difference linear voltage manostat, based on the circuit of being formed by efferent duct (103), error amplifier (102), reference voltage source (101), resistance pressure-dividing network (104) and load (105), it is characterized in that: the ON-OFF control circuit (308) that it also comprises an on-off circuit (307) and is attached thereto, wherein:

On-off circuit (307) is used to control the connection of the substrate electric potential of efferent duct (103);

ON-OFF control circuit (308) is used for controlling the conduction status of described on-off circuit (307) switch.

2. the circuit of enhancing driving capability of low voltage-difference linear voltage manostat according to claim 1 is characterized in that: described on-off circuit (307) comprises two metal-oxide-semiconductors (MP1, MP2) and a phase inverter (INV).

3. the circuit of enhancing driving capability of low voltage-difference linear voltage manostat according to claim 2 is characterized in that: described two metal-oxide-semiconductors (MP1, MP2) form not the switch of conducting simultaneously.

4. the circuit of enhancing driving capability of low voltage-difference linear voltage manostat according to claim 3, it is characterized in that: the described two switches not mode of conducting simultaneously are: when first metal-oxide-semiconductor (MP1) conducting, the substrate of efferent duct (MPX) is received input voltage (VIN), is normal conditions; When second metal-oxide-semiconductor (MP2) conducting, the substrate electric potential of efferent duct (MPX) is received output voltage (VOUT), produces a VSB voltage this moment.

5. the circuit of enhancing driving capability of low voltage-difference linear voltage manostat according to claim 1, it is characterized in that: described ON-OFF control circuit (308) is made of comparer, resistance (R3) and a current source (ISR) with hysteresis characteristic, the negative terminal of comparer connects output voltage (VOUT), the reference potential that produces between positive termination one current source and resistance.

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