CN101839941A - signal sense amplifier - Google Patents

本发明公开了一种信号感测放大器，包括差分跨导输入电路、差分共源共栅转导放大电路和有源负载电路；差分跨导输入电路为一个具有对称结构能实现宽共模输入范围的电压到电流差分输入级；差分共源共栅转导放大电路包括相同类型和尺寸的晶体管M₅和M₆，C_B3和C_B4分别与M₅与M₆的源极连接并提供直流电流偏置。本发明提供了一种能优先支持CMOS工艺的宽共模输入，特别是能宽于供电电压轨的高速、高精度、低压、低功耗的感测放大器，该电路不受工艺、供电电压、温度(PVT)漂移的影响，既能作为比较器功能又能作为放大器功能来实现电流检测或感测电路。

The invention discloses a signal sensing amplifier, which comprises a differential transconductance input circuit, a differential cascode transconductance amplifying circuit and an active load circuit; the differential transconductance input circuit is a symmetrical structure capable of realizing a wide common-mode input range The voltage-to-current differential input stage; the differential cascode transconductance amplifier circuit includes transistors M ₅ and M ₆ of the same type and size, C _B3 and C _B4 are respectively connected to the sources of M ₅ and M ₆ and provide DC current bias. The present invention provides a wide common-mode input that can preferentially support CMOS technology, especially a high-speed, high-precision, low-voltage, low-power sense amplifier that can be wider than the power supply voltage rail. The circuit is not affected by technology, power supply voltage, The effect of temperature (PVT) drift can be implemented as either a comparator function or an amplifier function to implement a current sense or sense circuit.

Signal sensing amplifier

Affiliated technical field

The present invention relates to a kind of signal sensing amplifier, especially, a kind of low pressure, low-power consumption, common-mode input range can be widened the high speed sense amplifying circuits to the power supply supply voltage rail, and it is used for current status to power supply equipment current delivery passage and detects or the channel current size is carried out sensing.

Background technology

At present, in many consumer electronics, communication apparatus, the computer equipment power supply, often need carry out the direct current conversion process, to satisfy unequally loaded supply voltage demand.In these were used, typical converter was the DC-DC converter, and it has occupied a large amount of volume, power consumption and the costs of electronic equipment.Electronic equipment development in future trend is low pressure, low-power consumption, miniaturization and cost degradation, this just needs the design of DC-DC converter circuit towards low pressure, low-power consumption, high-level efficiency development, the switching frequency of DC-DC converter is towards high frequency development (switching frequency is that the DC-DC converter of ten order of megahertz is a development in future trend), and manufacture craft aspect court is the CMOS technological development cheaply.Transient response speed is fast, control is simple because current-control type DC-DC converter has, be easy to compensate, high-precision output voltage and inherent control and limitation capability to the power switch electric current, therefore the DC-DC converter adopts current control mode more, but in the face of electronic equipment development in future trend, as the necessary current detecting of Current Control or current sensing circuit in low pressure, low-power consumption, at a high speed, be subjected to great challenge aspect the high precision.

In current control mode, controller need be understood the control signal that could determine after the current status information of current channel power switch.This just need carry out the real-time sensing of size of current to current channel, or the channel current state is carried out current detecting (detecting as peak point current state-detection, valley point current state-detection or zero current condition).For the sensing of size of current, its output waveform is passage waveform voltage or the current waveform behind the constant convergent-divergent in proportion.And to the detection of current status, its output waveform is a digital level, and detected waveform is corresponding digital level state with regard to saltus step after sensed current reaches predefined thresholding.

With CMOS technology cheaply is example, and theoretically, current detecting or sensing circuit have signal input and source signal to import dual mode.It is narrow to adopt the structure of grid input signal to be subject to common-mode input range, can not effectively operate in beyond its power supply supply voltage rail, its application scenario be limited in that common mode detects or sensing voltage at the supply voltage rail with interior or slightly wide occasion.Can better describe this situation by Fig. 1 a, described the traditional amplifier with folded common source and common grid structure in Fig. 1 a, this amplifier gain is higher, but its input common-mode range need guarantee to allow difference input pipe M ₁, M ₂Do not enter linear zone, must guarantee its current offset source C yet _B2And C _B3Operate as normal, thus make its common-mode input range have a upper limit, and the maximal value of its common-mode input range is:

V _{CM_MAX}＝V _DD+V _TH-V _CB23 (1)

Wherein:

V _DDIt is supply voltage;

V _THBe differential pair tube M1, the threshold voltage of M2;

V _CB23Be current source C _B2And C _B3The minimum voltage difference that its two ends need during operate as normal.

From formula (1) as can be seen, the highest input common mode voltage of this circuit is limited by the threshold voltage of its supply voltage, differential pair crystal and current source minimum operationg pressure differential.Aspect speed, the common source circuit can influence its response speed owing to the Miller phenomenon of differential pair tube mostly.

So operate in power supply supply voltage rail situation in addition for common mode detection or sensing voltage, generally use common gate mode by the source electrode input signal, though general common grid input method can produce the differential mode computing and circuit is simple, low in energy consumption, but the asymmetry of its structure, particularly under CMOS technology, make its performance be subjected to the influence of technology, supply voltage and temperature (PVT) drift serious, robustness is relatively poor, especially it is simple in structure, be difficult to improve its gain bandwidth product, cause its speed and precision limited.Can better describe this situation by Fig. 1 b, describe the both-end that adopts the source electrode input signal among Fig. 1 b and arrive single-ended differential mode amplifier, wherein M ₁The employing diode connects, with V _1NSignal is coupled to M ₂Grid and M ₂Source signal V _IPForm the differential mode computing, but because the asymmetry of this structure, on the one hand when this circuit when device uses as a comparison its threshold value to be subjected to the influence of PVT drift serious, on the other hand when this structure is used as amplifier, owing to M ₂Drain electrode as output, make the direct current fluctuation of output voltage can cause M ₁And M ₂The dc point of drain voltage does not match, and this will worsen input offset voltage.And this structure output terminal equals M to the common mode admittance of input end ₂Mutual conductance, cause its common-mode rejection ratio extremely low.Its gain characteristic is subject to M ₂The highest-gain characteristic be M ₂Self mutual conductance g _m(M ₂) divided by its source stray admittance g _Ds(M ₂), if will strengthen its gain or common-mode rejection ratio or M ₁And M ₂Match condition then need connect commonsource amplifier in back level, but like this can be because the Miller phenomenon that common source is introduced and seriously limit its bandwidth.

Summary of the invention

Drawback in view of prior art, the object of the present invention is to provide a kind of wide common-mode input range that can preferentially support CMOS technology, particularly can be wider than high speed, high precision, the low pressure of supply voltage rail, the sensing amplifier of low-power consumption, this circuit is not subjected to the influence of technology, supply voltage, temperature (PVT) drift, and the device function realizes that current detection circuit can realize current sensing circuit as the amplifier function again as a comparison.

Therefore, the technical scheme of sensing amplifier of the present invention comprises differential transconductance input circuit, difference cascode transduction amplifying circuit and active pull-up circuit as shown in Figure 2.Described differential transconductance input circuit is one and has voltage that symmetrical structure can realize wide common-mode input range to the current-differencing input stage, comprises (M ₁, M ₂) and (M of the generation difference current that constitutes ₃, M ₄) another of the generation difference current that constitutes, M ₁～M ₄Be the transistor of same type, wherein, M ₁With M ₄Measure-alike, M ₂And M ₃Measure-alike.And M ₁And M ₄All adopt diode to connect and respectively by C _B1And C _B2Provide the DC current biasing, M ₁With M ₃Source electrode (or emitter) link together, constitute an input end of differential input stage, M ₄With M ₂Source electrode (or emitter) link together, constitute another input end of differential input stage, M ₂And M ₃Drain electrode (or collector) link to each other with the next stage input end as the output terminal of difference current; Described difference cascode transduction amplifying circuit comprises the transistor M of same type and size ₅And M ₆, C _B3And C _B4Respectively with M ₅And M ₆Source electrode (or emitter) connect and DC current biasing be provided, this tie point is as the difference current input end of the corresponding levels, M ₅And M ₆Grid (or base stage) has common DC voltage biasing V _B, M ₅And M ₆Drain electrode separately links to each other with active pull-up circuit and forms the output terminal of signal amplification as sensing amplifier of the present invention.

The present invention utilizes source electrode (or emitter) input differential signal, has the input common mode voltage of wide region, and circuit adopts symmetrical structure to have robustness preferably, and internal signal transmits with current system, can realize that high gain-bandwidth is long-pending with miniwatt, and response speed is fast.Below explain detailedly with the specific embodiment conjunction with figs. so that be easier to understand purpose of the present invention, technology contents, characteristics and effect thereof.

Description of drawings

The collapsible common source and common grid amplifier of Fig. 1 a tradition grid input signal

The sensing amplifier of Fig. 1 b tradition source electrode input signal

Fig. 2 sensing amplifier block diagram of the present invention

An example circuit diagram of Fig. 3 a sensing amplifier of the present invention

Another example circuit diagram of using of device as a comparison of Fig. 3 b sensing amplifier of the present invention

Fig. 4 a adopts one of them typical case of the current sensing circuit of Fig. 3 a example circuit to use

The simulation waveform that Fig. 4 b adopts one of them typical case of the current sensing circuit of Fig. 3 a example circuit to use

The specific embodiment of the present invention

(1) invention block diagram technology is set forth

The technical scheme of sensing amplifier of the present invention comprises differential transconductance input circuit, difference cascode transduction amplifying circuit and active pull-up circuit as shown in Figure 2.Described differential transconductance input circuit is one and has voltage that symmetrical structure can realize wide common-mode input range to the current-differencing input stage, comprises (M ₁, M ₂) and (M of the generation difference current that constitutes ₃, M ₄) another of the generation difference current that constitutes, M ₁～M ₄Be the transistor of same type, wherein, M ₁With M ₄Measure-alike, M ₂And M ₃Measure-alike, M ₁Or M ₄With M ₂Or M ₃Equivalent breadth length ratio be M: N.And M ₁And M ₄All adopt diode to connect and respectively by C _B1And C _B2Provide the DC current biasing, M ₁With M ₃Source electrode (or emitter) link together, constitute an input end V of differential input stage _IP, M ₄With M ₂Source electrode (or emitter) link together, constitute another input end V of differential input stage _IN, V at this moment _IPAC portion pass through M ₁Be directly coupled to M ₂Grid (or base stage), V _INAC portion pass through M ₄Be directly coupled to M ₃Grid (or base stage), M ₂And M ₃Drain electrode (or collector) as difference current (Δ i _D1, Δ i _D2)Output terminal, and satisfy:

Δ i D 2 = - Δ i D 1 = Δv · g m ( M 2 , M 3 ) - - - ( 2 )

Δ v is the pressure reduction of input end.

It is the common-mode input range that can not had the upper limit in theory that this input stage adopts the advantage of source electrode (emitter) input signal, and its minimum input common mode voltage is:

V CM _ MIN = V SG ( M 1 , 4 ) + V C B 1.2 - - - ( 3 )

Wherein:

Difference current (Δ i _D1, Δ i _D2) output terminal link to each other with the input end of described difference cascode transduction amplifying circuit, comprise the transistor M of same type and size ₅And M ₆, C _B3And C _B4Respectively with M ₅And M ₆Source electrode (or emitter, preferred FET) connect and the DC current biasing be provided, this tie point is as the difference current input end of the corresponding levels, M ₅And M ₆Grid (or base stage) has common DC voltage biasing V _B, especially work as V _BWhen adopting the cascode structure that gain strengthens, make M ₅And M ₆The node impedance that the source electrode place is arranged lower, make the inferior limit of this point at high frequency treatment, thereby obtain good frequency response.M ₅And M ₆Drain electrode separately links to each other with active pull-up circuit and forms the output terminal of signal amplification as sensing amplifier of the present invention.Active load generally adopts the current mirror mode, thereby especially the cascade interface that strengthens of cascode structure or gain can obtain high output impedance and obtains high output gain, and its every dc bias current is:

I active _ load = I C B 3.4 - N M I C B 1.2 - - - ( 4 )

So C _B3And C _B4Bias current must be enough greatly, to satisfy the direct current biasing demand of active load.

Bias voltage V _BMust be enough high to satisfy cascade transduction amplifier operate as normal, with respect to power rail V _PS2, V _BThe condition that needs to satisfy is:

V B > V GS ( M 5,6 ) + V C B 3.4 - - - ( 5 )

Wherein:

V _{GS (M5,6)}Be M ₅, M ₆Grid source (base-emitter) driving voltage

Be C _B3, C _B4Minimum

Simultaneously, the simulation output area of sensing amplifier is subjected to V _BWith the restriction of active pull-up circuit structure, its minimum output voltage is by V _BBe restricted to:

V _O(min)＝V _B-V _TH (5)

Wherein:

V _THThreshold voltage for MOSFET.

(2) example of sensing amplifier shown in Fig. 3 a and the typical case's application (Fig. 4) in current sense thereof is set forth

This circuit is single-ended output, and the highest of output area is than the low 0.2V of supply voltage, and its DC current gain equals 2g _{M (M2,3)}* r _{O (M12)}, g wherein _{M (M2,3)}Be M ₂And M ₃Mutual conductance, r _{O (M12)}Be M ₁₂Output impedance.

Fig. 4 a is for adopting the example that the typical case uses in current sense of this Fig. 3 a amplifier, and is wherein identical with Fig. 3 a amplifier in the frame of broken lines s; Supply voltage V _DDBe 5V, M _SWBe current switch, M _P1Be current sense pipe, M _P1Size and M _SWRatio be 2: 10 ⁵, they have drive signal V _DRVV is worked as in control _DRVElectric current is closed during=5V, works as V _DRV=0 o'clock electric current I _LBy.The static input current of amplifier is I _B=2uA, M _P2Link to each other with the output of amplifier and back linking to each other constitute negative feedback, M with the negative terminal input vin of amplifier _P2Also can make M among Fig. 3 a ₁₁And M ₁₂More symmetrical, work as V _DRV, force M at=0 o'clock _P1And M _SWBoth end voltage is identical, passes through I _CCompensation, thereby the electric current I that senses _SensBe I _L2/10 ⁵, this function of current is to wave filter R _SAnd C _SAfter output voltage V _SenseShown in Fig. 4 b, waveform can satisfy the demand of high frequency switch power less than 50ns Time Created.

(3) sensing amplifier example shown in Fig. 3 b is set forth

This circuit is single-ended output, has symmetrical structure, and gain reaches g _{M (M2,3)}r _{O (M12)}g _{M (m13)}r _{O (m13)}, be suitable as that comparer detects at current detecting such as peak current detection, valley point current, use in the zero passage detection.

Below the useful result of this circuit comprises as can be known:

(a), common-mode input range is big, the minimum value of input common mode voltage is V in theory _TH+ 2V _OV, there is not higher limit, can reach any high pressure that technology is supported, wherein V _THBe transistorized threshold voltage (about 0.7V), V _OV(0.1V～0.2V) is generally got in board design for its overdrive voltage;

(b), whole signal flow is by the source electrode or the emitting stage input of differential mode, reduced the Miller phenomenon, response speed is fast, can under miniwatt, realize big gain bandwidth product, and differential mode can make the input dc offset voltage be subjected to the influence of technology, supply voltage, temperature (PVT) drift little, also makes entire circuit have stronger common mode inhibition capacity.