CN102368683B - Low power consumption weak signal amplification shaping circuit - Google Patents

Abstract

The invention discloses a low power consumption weak signal amplification shaping circuit, which relates to the technology of integrated circuits and comprises a reference source circuit, an amplification circuit and a Schmitt trigger shaping circuit, wherein the amplification circuit consists of an opa (optoelectronic pulse amplifier), two capacitors and two PMOS (positive channel metal oxide semiconductor) tubes, the Schmitt trigger shaping circuit consists of three PMOS tubes, three NMOS (N-Metal-Oxide-Semiconductor) tubes, an inverter INV and an SR (Synchronous Reset) trigger, and the reference source circuit consists of two PMOS tubes, two NMOS tubes and three resistors. In the invention, a flip threshold controllable mixed mode Schmitt trigger is adopted, and three equally-spaced negative temperature coefficient reference voltage offset pre-amplification circuits and Schmitt triggers are used so as to ensure the circuit of higher precision under any PVT (process verification test) conditions. The circuit disclosed by the invention has lower power consumption, and simultaneously has higher PVT change resisting capacity.

Description

A kind of low power consumption weak signal amplification shaping circuit

Technical field

The present invention relates to technical field of integrated circuits, is a kind of low power consumption weak signal amplification shaping circuit, and small-signal such as square wave, the amplification such as sinusoidal wave also is shaped as the circuit of full width of cloth square wave.

Background technology

Along with developing rapidly of integrated circuit manufacturing industry, high density, high-performance, low cost, low-power consumption have become the main body trend of integrated circuit (IC) design development.Progressively popularizing of wireless mobile technology is so that this design requirement of low-power consumption becomes particularly urgent.

The signal of millivolt and following magnitude thereof is called as small-signal.Weak signal amplification shaping circuit is widely used in the systems such as biological signal collecting, RFID, wireless electron charge, radio sensing network, Internet of Things.For example in highway wireless electron Fare Collection System [GB/T 20851-2007], in order to reduce system energy consumption, generally adopt sleep-awake mechanism.Its basic functional principle is: wake carrier signal up by the base station emission, portable terminal receives carrier wave and restores wake-up signal, wake-up signal after the reduction is generally continuous faint square signal, after this faint square signal need to amplify the square-wave signal that is shaped as the full width of cloth, send into again subsequent module and carry out analyzing and processing.

Power consumption is to weigh an important indicator of weak signal amplification shaping circuit.The powered battery mode is all adopted in a lot of application scenarios at weak signal amplification shaping circuit.In order to prolong battery-powered time, under the prerequisite that guarantees systematic function, circuit power consumption requires in 10uA magnitude or following.

Sensitivity is another important indicator of weighing weak signal amplification shaping circuit.Weak signal amplification shaping circuit requires sensitivity moderate.Sensitivity is too little, is subjected to easily the impact of noise and other interference; Sensitivity is too large, does not reach again the sensitivity requirement of system.

Resisting temperature, supply voltage and process corner (PVT) changing capability is to weigh the index whether a Circuits System is fit to large-scale industrial production.In order to improve the demand under yields and the different application condition, the anti-PVT characteristic of circuit is more strong better.

The general implementation method that small-signal is amplified shaping is first small-signal to be amplified, and then is shaped as full width of cloth Digital Square-Wave by Schmidt trigger.Yet the turn threshold of traditional Schmitt trigger circuit is very responsive to the variation of PVT.In order to keep the excursion of the signal amplitude covering turn threshold after amplifying circuit amplifies, the amplifying circuit of prime needs very high multiplication factor.In order to reach so high multiplication factor, amplifying circuit need to consume a large amount of electric currents.In addition, the change of turn threshold can cause the change of output square-wave signal duty ratio after the shaping.On the other hand, the power consumption of traditional Schmidt trigger is also very responsive to the variation of PVT.

Summary of the invention

The objective of the invention is to announce a kind of low power consumption weak signal amplification shaping circuit, the signals such as faint square wave, sine wave can be amplified and be shaped as full width of cloth square wave, the accuracy height of shaping.

The present invention adopts following technical scheme to achieve these goals:

A kind of low power consumption weak signal amplification shaping circuit amplifies faint square wave, sine wave signal and is shaped as full width of cloth square wave; It comprises reference source circuit, amplifying circuit and Schmidt trigger shaping circuit; Wherein, reference circuit comprises two PMOS pipe PMr ₁, PMr ₂, two NMOS pipe NMr ₁, NMr ₂With three resistance R ₁, R ₂, R ₃Amplifying circuit comprises an amplifier opa, two capacitor C 1, C2, two PMOS pipe NMo ₁, NMo ₂The electric resistance structure that cascade forms; Schmitt trigger circuit comprises three PMOS pipe PMs ₁, PMs ₂, PMs ₃, three NMOS pipe NMs ₁, NMs ₂, NMs ₃, inverter INV and a set-reset flip-floop;

The PMr of reference source circuit ₁Pipe and PMr ₂The source electrode of pipe meets respectively power supply, PMr ₁The pipe drain electrode meets respectively NMr ₁Pipe drain electrode and NMr ₂Tube grid; PMr ₁Tube grid respectively with PMr ₂Tube grid, drain electrode and NMr ₂The pipe drain electrode is electrically connected; NMr ₂Tube source grade is through the resistance R of series connection ₁, R ₂, R ₃Meet respectively NMr ₁Pipe source electrode and ground; NMr ₂Tube source grade and resistance R ₁Contact and NMs ₂Tube grid is electrically connected; Resistance R ₁With resistance R ₂Contact respectively with NMr ₁Tube grid and amplifier opa positive input terminal are electrically connected;

The capacitor C 1 one termination input signals of pre-amplifying circuit, the other end is electrically connected with amplifier opa negative input end; NMo ₁Pipe and NMo ₂After the pipe serial connection, two ends are in parallel with capacitor C 2, and are connected across between the negative input end, output of amplifier opa; Amplifier out and NMs ₁Tube grid is electrically connected;

Three PMs of Schmidt trigger ₁, PMs ₂, PMs ₃The source electrode of pipe connects respectively power supply, three NMs ₁, NMs ₂, NMs ₃The source electrode of pipe is ground connection respectively; PMs ₁Pipe drain electrode, three PMs ₁, PMs ₂, PMs ₃Tube grid, NMs ₁The pipe drain electrode is electrically connected; PMs ₂Pipe drain electrode, NMs ₂The S utmost point of pipe drain electrode, set-reset flip-floop is electrically connected; PMs ₃Pipe drain electrode, NMs ₃The input of pipe drain electrode, inverter INV is electrically connected; The output of inverter INV is electrically connected with the R utmost point of set-reset flip-floop; The Q of set-reset flip-floop very exports.

Described low power consumption weak signal amplification shaping circuit, its described Schmidt trigger is modulus mixed mode Schmidt trigger, its V _IH, V _ILProvided by reference source circuit.V _IH, V _ILThe negative input end that connects respectively two comparators.Vin connects the positive input terminal of two comparators, respectively and V _IH, V _ILRelatively export by comparator, obtain digital signal A, B.It is non-that B obtains B through inverter.A and B are non-again through set-reset flip-floop output.Set-reset flip-floop is built by two NAND gate.When Vin greater than V _IH, SR is output as 0, when Vin is reduced to V _ILAnd V _IHBetween the time, circuit output remains unchanged, until Vin is reduced to V _ILBelow, it is 1 that set-reset flip-floop output just can be overturn; In like manner, when Vin voltage less than V _IL, set-reset flip-floop is output as 1, when Vin voltage is increased to V _ILAnd V _IHBetween, the set-reset flip-floop output state remains unchanged, and only has as Vin to be increased to V _IHWhen above, the set-reset flip-floop output state just can change.

Described low power consumption weak signal amplification shaping circuit, its described amplifying circuit can be isolated the direct current signal of weak signal, thereby prevents the DC maladjustment that the signal source direct current signal causes.

Described low power consumption weak signal amplification shaping circuit, two resistance R of its described reference source circuit ₁, R ₂Equivalence, reference source circuit provides biasing V for amplifier opa ₀, for comparator provides biasing V _IHAnd V _IL, pass through resistance R ₁, R ₂The constant resistance dividing potential drop, V _IH, V ₀, V _ILMagnitude of voltage becomes uniformly-spaced, and the pre-flat V of amplifying circuit output DC ₁Equal V ₀Thereby, V _IH, V ₁, V _ILMagnitude of voltage becomes uniformly-spaced, and namely three of Schmidt trigger input DC level become uniformly-spaced, have guaranteed the accuracy of Schmidt trigger shaping.

The DC maladjustment that signal amplification shaping circuit of the present invention, the amplification circuit structure of employing can stop weak signal to be introduced.Simultaneously, adopt the controlled mixed mode Schmidt trigger of a kind of turn threshold, and use three equally spaced negative temperature coefficient reference voltage biasings, guaranteed the accuracy of shaping.Sensitivity of the present invention is inferior millivolt magnitude, and power consumption is the microampere magnitude.

Description of drawings

Fig. 1 is a kind of low power consumption weak signal amplification shaping circuit structural representation of the present invention;

Fig. 2 is amplifying circuit schematic diagram in the signal amplification shaping circuit of the present invention;

Fig. 3 is the operation amplifier circuit figure that amplifying circuit adopts in the signal amplification shaping circuit of the present invention;

Fig. 4 is mixed mode Schmidt trigger principle schematic in the signal amplification shaping circuit of the present invention;

Fig. 5 is the comparator circuit figure that Schmidt trigger adopts in the signal amplification shaping circuit of the present invention;

Fig. 6 is weak signal amplification shaping circuit figure in the signal amplification shaping circuit of the present invention;

Fig. 7 is embodiments of the invention circuit input faint square signal simulation waveform figure;

Fig. 7 (a) embodiment is input as the faint square signal with slow edge of 2mV;

Fig. 7 (b) embodiment input signal is through the output waveform behind the pre-amplifying circuit;

The full width of cloth square-wave signal of the final output of Fig. 7 (c) embodiment system;

Fig. 8 is embodiments of the invention circuit input Weak Sinusoidal Signal simulation waveform figure;

Fig. 8 (a) input peak value is the sinusoidal signal of 2mV;

The waveform of Fig. 8 (b) signal after the embodiment amplifying circuit amplifies;

Waveform after Fig. 8 (c) embodiment shaping;

Fig. 9 is that embodiments of the invention Circuits System power consumption is with supply voltage and temperature changing curve diagram;

Fig. 9 (a) embodiment system power dissipation electric current varies with temperature curve;

The system power dissipation electric current was with the mains voltage variations curve when Fig. 9 (b) embodiment temperature was 27 ℃;

Figure 10 is that the sensitivity of embodiments of the invention Circuits System is with supply voltage and temperature changing curve diagram;

Figure 10 (a) varies with temperature curve for the embodiment circuit sensitivity;

Figure 10 (b) for exemplary circuit when temperature is 27 ℃ sensitivity with the mains voltage variations curve.

Embodiment

Below in conjunction with accompanying drawing technical scheme of the present invention is elaborated.

Fig. 1 is the system construction drawing of weak signal amplification shaping circuit.Whole system mainly is comprised of three modules: reference source circuit module, amplifying circuit module, mixed mode Schmidt trigger module.Reference source circuit provides electric current and voltage reference for other each modules.Amplifying circuit amplifies the small-signal of input, and the mixed mode Schmidt trigger carries out shaping to the signal after amplifying, and obtains desirable full width of cloth output square-wave signal.

Figure 2 shows that the amplifying circuit schematic diagram.The DC maladjustment that this structure can stop front stage circuits to be introduced has the advantages such as low-power consumption simultaneously.Its multiplication factor is

$G=\frac{\frac{1}{\mathrm{jw}{C}_2}}{\frac{1}{\mathrm{jw}{C}_1}}=\frac{C_1}{C_2}---\left(1\right)$

The opa output dc voltage equates with opa negative input end voltage.Because the short characteristic of the void of opa, opa positive-negative input end direct voltage equates, thereby the output dc voltage Vout of pre-amplifying circuit equals Vref.Vout passes through resistance R ₁Provide direct current biasing to the opa negative input end.Because the appearance value of electric capacity is less in the integrated circuit, its equiva lent impedance is more than M ohm.In order to make resistance R ₁Do not affect the multiplication factor of amplifying circuit, its resistance need to be far longer than the equiva lent impedance of capacitor C 2.The resistance of so large resistance can take a large amount of chip areas.In order to save area, R ₁The PMOS pipe that is formed by two cascades substitutes, and its resistance can reach G ohm magnitude.Opa adopts traditional difference input Single-end output structure herein, as shown in Figure 3.

Small-signal needs be shaped as through Schmidt trigger the square-wave signal of the full width of cloth through after amplifying in advance.Schmidt trigger is shaping circuit commonly used, and the edge can being changed slowly, waveform shaping signal is the precipitous square wave in edge.Schmidt trigger can also be removed the noise that is superimposed upon on the signal effectively.When the shaping square wave, the duty ratio that can also guarantee to export rear square-wave signal is constant.

Traditional digital Schmitt trigger threshold value trigging signal V _IH, V _ILVariation with supply voltage and technique changes, and does not meet the accuracy requirement of weak signal amplification shaping circuit.For example work as V _IH, signal DC level, V _ILBe not uniformly-spaced, and signal just within the whole cycle amplitude do not arrive another turn threshold to arrive one of them turn threshold only, then Schmidt trigger output is constant, shaping feature lost efficacy.Give one example again, amplify in the shaping process at faint square signal, work as V _IH, V _ILWhen becoming uniformly-spaced with the square wave intermediate level, duty cycle square wave is constant after the shaping; Work as V _IH, V _ILChange V _IH, V _ILNo longer become uniformly-spaced with the square wave intermediate level, the duty cycle square wave after the shaping just can change.Simultaneously, conventional digital Schmidt trigger static current of lcd is very sensitive to the variation of supply voltage and temperature, and power consumption is too high, and circuit can produce the energy consumption waste; Power consumption is excessively low, and circuit then can the driving force deficiency.

The present invention has adopted a kind of modulus mixed mode Schmidt trigger, as shown in Figure 4, and the turn threshold V of this structure Schmidt trigger _IH, V _ILProvided by reference source circuit.V _IH, V _ILThe negative input end that connects respectively two comparators.Vin connects the positive input terminal of two comparators, respectively and V _IH, V _ILRelatively export by comparator, obtain digital signal A, B.It is non-that B obtains B through inverter.A and B are non-again through set-reset flip-floop output.Set-reset flip-floop is built by two NAND gate.When Vin greater than V _IH, SR is output as 0, when Vin is reduced to V _ILAnd V _IHBetween the time, circuit output remains unchanged, until Vin is reduced to V _ILBelow, it is 1 that set-reset flip-floop output just can be overturn; In like manner, when Vin voltage less than V _IL, set-reset flip-floop is output as 1, when Vin voltage is increased to V _ILAnd V _IHBetween, the set-reset flip-floop output state remains unchanged, and only has as Vin to be increased to V _IHWhen above, the set-reset flip-floop output state just can change.

Two comparators that Schmidt trigger adopts can be simplified to a circuit, as shown in Figure 5, and PMs ₁, PMs ₂, PMs ₃Measure-alike, consist of current-mirror structure; NMs ₁, NMs ₂, NMs ₃Measure-alike.

The present invention adopts V _GS/ R type reference source circuit structure is shown in Fig. 6 left side.PMr ₁And PMr ₂Consist of current mirror, NMr ₁Grid be connected to resistance R ₂Anode, R ₂Be negative temperature coefficient.Because the threshold voltage of metal-oxide-semiconductor is negative temperature coefficient, when its gate source voltage temperature coefficient also when negative and identical with the temperature coefficient of threshold voltage, the overdrive voltage that flows through metal-oxide-semiconductor is constant, thus the current value maintenance of flowing through metal-oxide-semiconductor is constant.V _GS/ R type a reference source is exactly a kind of reference source circuit that forms according to this principle.By choosing suitable NMr ₁Breadth length ratio and R ₂, R ₃The resistance value sum, namely can obtain a reference current value Iref with temperature and independent of power voltage.The zero-temperature coefficient reference current flows through negative temperature coefficient resister R ₁, R ₂And R ₃, obtain three negative temperature coefficient reference voltage V _IH, V ₀And V _IL

The present invention has adopted a kind of biasing means, as shown in Figure 6, uses three equally spaced negative temperature coefficient reference voltages setover pre-amplifying circuit and Schmidt trigger.This biasing means does not namely affect the reference source circuit normal operation, guarantees again the accuracy of Schmidt trigger.

Among Fig. 6, the left side is reference source circuit, and the centre is amplifying circuit, and the right is Schmidt trigger.Reference source circuit provides biasing V for the opa positive input terminal ₀, for Schmidt trigger provides biasing V _IHAnd V _ILAs can be seen from the figure, by constant resistance dividing potential drop, V _IH, V ₀, V _ILMagnitude of voltage becomes uniformly-spaced.And the pre-flat V of amplifying circuit output DC ₁Equal V ₀Thereby, V _IH, V ₁, V _ILMagnitude of voltage becomes uniformly-spaced.Be that three input DC level of Schmidt trigger become uniformly-spaced.DC level becomes uniformly-spaced, can guarantee that output is being shaped waveform (V ₁) first cycle and second symmetric points place in cycle change state, this has guaranteed the accuracy of weak signal amplification shaping circuit.If the input small-signal is faint square wave, it is identical with the duty ratio of input square wave also can to guarantee to export square wave.

The below is for an embodiment:

Embodiment adopts TSMC 0.18-um 3V-CMOS technique to realize as shown in Figure 6 circuit.

Fig. 7 be the embodiment circuit at supply voltage 3.3V, Simulation results during 27 ℃ of temperature.Be input as the faint square signal with slow edge of 2mV, shown in Fig. 7 (a).Fig. 7 (b) for input signal through the output waveform behind the pre-amplifying circuit.Fig. 7 (c) is the full width of cloth square-wave signal of the final output of system.As we know from the figure, the faint square signal of input is converted to the constant full width of cloth square-wave signal of the precipitous duty ratio in edge via amplifying circuit.

Fig. 8 is that the Weak Sinusoidal Signal of amplitude 2mV frequency 14kHz is through the oscillogram of embodiment weak signal amplification shaping circuit.Fig. 8 (a) is the sinusoidal signal of 2mV for the input peak value, and Fig. 8 (b) is the waveform of signal after amplifying circuit amplifies, and Fig. 8 (c) is the waveform after the shaping.

Fig. 9 is that embodiment Circuits System power consumption is with temperature and mains voltage variations curve.By the power constraints scheme, system power dissipation is with temperature and mains voltage variations kept stable.Fig. 9 (a) varies with temperature curve for the system power dissipation electric current, and at-40 ℃-120 ℃, system power dissipation has only changed 0.08 μ A.The system power dissipation electric current was with the mains voltage variations curve when Fig. 9 (b) was 27 ℃ for temperature, and when supply voltage changed to 3.3V from 1V, static current of lcd was substantially constant.

Sensitivity is the minimum signal amplitude that amplifying circuit can detect and amplify.Amplitude surpasses the difference V of the height turn threshold of Schmidt trigger after the pre-amplification of signal _IH-V _IL, namely can be detected and amplify.The as can be known sensitivity of system:

$V_{\min }=\frac{H_{\mathrm{IH}}-V_{\mathrm{IL}}}{G}=\frac{2{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000119444290000022.png"\; state="\{\{state\}\}">R</figure-callout>}}_1\&CenterDot;I_{\mathrm{<figure-callout\; id="1"\; label="ref\; C"\; filenames="HDA0000119444290000022.png"\; state="\{\{state\}\}">ref</figure-callout>}}}{C_{}}=\frac{{2\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000119444290000022.png"\; state="\{\{state\}\}">R</figure-callout>}}_1\&CenterDot;I_{\mathrm{ref}}\&CenterDot;C_2}{C_1}---\left(2\right)$

Wherein, R ₁The resistance R of reference source circuit in the representative graph 6 ₁Resistance, C1, C2 represent the capacitance of pre-amplifying circuit.In actual applications, sensitivity need to remain within the rational scope, and sensitivity is too little, is subject to easily the impact of noise and other interference, and sensitivity is too large, then can lose useful small-signal.Can find out from formula (2), by regulating R ₁Set suitable system sensitivity with the ratio of C1/C2.

Figure 10 (a) varies with temperature curve for the embodiment circuit sensitivity, and at-40 ℃-120 ℃, sensitivity remains within the rational scope.Sensitivity is with the mains voltage variations curve when temperature is 27 ℃ for exemplary circuit for Figure 10 (b), and when supply voltage changed to 3.3V from 1V, sensitivity kept 760 μ V constant.

Under different PVT conditions the embodiment circuit is carried out emulation, the result shows that system sensitivity all remains within the rational scope under different PVT conditions with power consumption.

Claims (4)

1. low power consumption weak signal amplification shaping circuit amplifies faint square wave, sine wave signal and is shaped as full width of cloth square wave; It is characterized in that, comprise reference source circuit, amplifying circuit and Schmitt trigger circuit; Wherein, reference source circuit comprises two PMOS pipe PMr ₁, PMr ₂, two NMOS pipe NMr ₁, NMr ₂With three resistance R ₁, R ₂, R ₃Amplifying circuit comprises an amplifier opa, two capacitor C 1, C2, two PMOS pipe NMo ₁, NMo ₂The electric resistance structure that cascade forms; Schmitt trigger circuit comprises three PMOS pipe PMs ₁, PMs ₂, PMs ₃, three NMOS pipe NMs ₁, NMs ₂, NMs ₃, inverter INV and a set-reset flip-floop;

The PMr of reference source circuit ₁Pipe and PMr ₂The source electrode of pipe meets respectively power supply, PMr ₁The pipe drain electrode meets respectively NMr ₁Pipe drain electrode and NMr ₂Tube grid; PMr ₁Tube grid respectively with PMr ₂Tube grid, drain electrode and NMr ₂The pipe drain electrode is electrically connected; NMr ₂Tube source grade is through the resistance R of series connection ₁, R ₂, R ₃Meet respectively NMr ₁Pipe source electrode and ground; NMr ₂Tube source grade and resistance R ₁Contact and NMs ₂Tube grid is electrically connected; Resistance R ₁With resistance R ₂Contact respectively with NMr ₁Tube grid and amplifier opa positive input terminal are electrically connected;

The capacitor C 1 one termination input signals of amplifying circuit, the other end is electrically connected with amplifier opa negative input end; NMo ₁Pipe and NMo ₂After the pipe serial connection, two ends are in parallel with capacitor C 2, and are connected across between the negative input end, output of amplifier opa; Amplifier out and NMs ₁Tube grid is electrically connected;

Three PMs of Schmitt trigger circuit ₁, PMs ₂, PMs ₃The source electrode of pipe connects respectively power supply, three NMs ₁, NMs ₂, NMs ₃The source electrode of pipe is ground connection respectively; PMs ₁Pipe drain electrode, three PMs ₁, PMs ₂, PMs ₃Tube grid, NMs ₁The pipe drain electrode is electrically connected; PMs ₂Pipe drain electrode, NMs ₂The S utmost point of pipe drain electrode, set-reset flip-floop is electrically connected; PMs ₃Pipe drain electrode, NMs ₃The input of pipe drain electrode, inverter INV is electrically connected; The output of inverter INV is electrically connected with the R utmost point of set-reset flip-floop; The Q of set-reset flip-floop very exports.

2. low power consumption weak signal amplification shaping circuit as claimed in claim 1 is characterized in that, described Schmitt trigger circuit is modulus mixed mode Schmitt trigger circuit, its high threshold trigging signal V _IH, low threshold value trigging signal V _ILProvided by reference source circuit; V _IH, V _ILThe negative input end that connects respectively two comparators; Input Vin connects the positive input terminal of two comparators, respectively and V _IH, V _ILRelatively export by comparator, obtain digital signal A, B; It is non-that B obtains B through inverter; A and B are non-again through set-reset flip-floop output; Set-reset flip-floop is built by two NAND gate; When Vin greater than V _IH, SR is output as 0, when Vin is reduced to V _ILAnd V _IHBetween the time, circuit output remains unchanged, until Vin is reduced to V _ILBelow, it is 1 that set-reset flip-floop output just can be overturn; When Vin voltage less than V _IL, set-reset flip-floop is output as 1, when Vin voltage is increased to V _ILAnd V _IHBetween, the set-reset flip-floop output state remains unchanged, and only has as Vin to be increased to V _IHWhen above, the set-reset flip-floop output state just can change.

3. low power consumption weak signal amplification shaping circuit as claimed in claim 1 is characterized in that, described amplifying circuit can be isolated the direct current signal of weak signal, thereby prevents the DC maladjustment that the signal source direct current signal causes.

4. low power consumption weak signal amplification shaping circuit as claimed in claim 1 is characterized in that, two resistance R of described reference source circuit ₁, R ₂Equivalence, reference source circuit provides biasing V for amplifier opa ₀, for comparator provides high threshold trigging signal V _IHWith low threshold value trigging signal V _IL, pass through resistance R ₁, R ₂The constant resistance dividing potential drop, V _IH, V ₀, V _ILMagnitude of voltage becomes uniformly-spaced, and the flat V of amplifying circuit output DC ₁Equal V ₀Thereby, V _IH, V ₁, V _ILMagnitude of voltage becomes uniformly-spaced, and namely three of Schmitt trigger circuit input DC level become uniformly-spaced, have guaranteed the accuracy of Schmitt trigger circuit shaping.

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