CN201097247Y - A standard voltage source circuit - Google Patents

Abstract

The utility model discloses a bandgap voltage reference circuit with low sensitivity to power supply voltage change and high stability, comprising a power supply circuit and a power supply preliminary adjusting circuit. The voltage input terminal of the power supply preliminary adjusting circuit is connected with a power supply V d d and the preliminary power supply terminal of the power supply preliminary adjusting circuit is connected with the input terminal of the power supply circuit; the reference voltage output terminal of the power supply circuit is connected with the voltage feedback terminal of the power supply preliminary adjusting circuit and outputs reference voltage V e f. When the bandgap voltage reference circuit is in work, the output voltage is stable under different power supply voltages and is of low sensitivity to the change of the power supply voltage; the bandgap voltage reference circuit is capable of generating a reference voltage source with low temperature coefficient and reducing the sensitivity of the output voltage of the reference voltage source to the power supply voltage change; meanwhile, the bandgap voltage reference circuit increases the capability of resistance to the shaking of the power supply; the the bandgap voltage reference circuit is simple in structure and low in cost and is widely applicable.

Description

A kind of reference voltage source circuit

Technical field

The utility model relates to a kind of voltage source circuit, relates in particular to a kind of reference voltage source circuit that has power supply pre-adjustment circuit.

Background technology

In recent years, integrated circuit relates to technology along with technology has obtained development at full speed together.The chip system integrated technology has been received extensive concern.Further complicated along with circuit system structure, basic module to mimic channel, have higher requirement as circuit such as A/D, D/A converter, dynamic storage, phaselocked loops, high precision, high stability, high integration and low-power consumption become the main flow of design.All require to have chip integration in these integrated circuit and become the high-precision voltage reference source, its precision and stability directly affect the performance of total system, and therefore a good reference source is vital.One high-precision reference voltage source requirement temperature coefficient is little, power supply inhibition ability is strong.

Reference voltage source has a variety of implementations, for example, and all kinds of bandgap voltage references; With the gate source voltage of field effect transistor reference voltage source circuit as benchmark; With the threshold voltage of field effect transistor reference voltage source circuit as benchmark, or the like.

Bandgap voltage reference is relatively ripe, and it adopts bipolar device to realize that output voltage values is substantially constant at about 1.25V; Principle of work is that the positive temperature coefficient (PTC) of Δ Vbe and the drift that negative temperature coefficient produced of Vbe are cancelled out each other.Bandgap voltage reference is because control and adjusting easily has application scenario very widely.

With the gate source voltage of field effect transistor reference voltage source circuit as benchmark, threshold voltage and mobility temperature coefficient by field effect transistor carry out temperature compensation, perhaps the reference voltage of low-temperature coefficient is relatively simple for structure, but it is bigger to be subjected to the influence of integrated circuit technology line.

With the threshold voltage of the field effect transistor reference voltage source circuit of benchmark the most, obtain the reference voltage of low-temperature coefficient by the threshold voltage difference of two types of field effect transistor, aspect temperature coefficient, because threshold voltage has linear temperature coefficient, thereby temperature compensation is fairly simple, but similar with the gate source voltage of field effect transistor as the reference voltage source circuit of benchmark, also be subjected to the influence of processing line bigger.

For all kinds of reference voltage sources, inside usually produces bias current by constant-current source circuit, obtain each required branch current by current mirror, because the existence of channel length modulation effect, when supply voltage changed, the electric current of mirror image can produce bigger error, especially when using minimum length transistors, this has just caused the output valve of reference voltage source bigger to the sensitivity of mains voltage variations, and it is stable inadequately that reference voltage output becomes.

Traditional bandgap voltage reference comprises biasing circuit and reference voltage output circuit.Principle of work is: adopted negative temperature coefficient voltage and positive temperature coefficient (PTC) voltage to superpose by a certain percentage, realized the output reference voltage that low temperature floats.Biasing circuit provides a positive temperature coefficient (PTC) electric current to reference voltage output circuit, resistance R 2 two ends form the voltage of positive temperature coefficient (PTC), the Vbe of triode Q1 is a negative temperature coefficient, the voltage stack back of Positive and Negative Coefficient Temperature forms the benchmark output voltage V ref of low-temperature coefficient, and the output absolute value of the bandgap voltage reference of the next standard of normal temperature is 1.25V.Traditional bandgap voltage reference has simple characteristics, but the output valve of reference voltage source is to producing bigger variation with mains voltage variations.

Summary of the invention

At the problems referred to above, the purpose of this utility model is to design the reference voltage source circuit to the very little high stability of the sensitivity of mains voltage variations

The utility model adopts following technical scheme:

A kind of reference voltage source circuit, comprise voltage source circuit, power supply pre-adjustment circuit, the voltage input end of power supply pre-adjustment circuit meets power supply Vdd, its pre-adjustment power end connects the input power supply source end of voltage source circuit, the reference voltage output end of voltage source circuit connects the pressure feedback port of power supply pre-adjustment circuit, and output reference output voltage V ref.Described power supply pre-adjustment circuit comprises current source A1 and PMOS pipe M6, the end of current source A1 meets power supply Vdd as the voltage input end of power supply pre-adjustment circuit, the source electrode of its other end and PMOS pipe M6 is connected and links to each other with the input power supply source end of voltage source circuit as the pre-adjustment power end of power supply pre-adjustment circuit, output pre-adjustment voltage Vreg, the grid of PMOS pipe M6 is as the pressure feedback port of power supply pre-adjustment circuit, the output voltage signal of input voltage source circuit, the drain electrode of PMOS pipe M6 connects common.

The utility model also comprises anti-power supply dither circuit, and the filtering end of anti-power supply dither circuit is connected with the reference voltage output end of voltage source circuit.Described anti-power supply dither circuit comprises capacitor C 1, and capacitor C 1 one ends are connected with the reference voltage output end of voltage source circuit as the filtering end of anti-power supply dither circuit, another termination common of capacitor C 1.

Compared with prior art, when the reference voltage source circuit that has power supply pre-adjustment circuit of the present utility model was worked, output voltage is highly stable under the different electrical power voltage initial conditions, and was very little to the sensitivity of mains voltage variations; And can when obtaining the low-temperature coefficient reference voltage source, reduce the sensitivity of reference voltage source output voltage, strengthen the anti-power supply shake ability of circuit simultaneously mains voltage variations.Specify as follows:

1, the utility model provides a kind of reference voltage source circuit of high stability, on traditional all kinds of reference sources basis, increased power supply pre-adjustment circuit, produce a pre-adjustment voltage Vreg, characteristics according to PMOS pipe steady current, produce constant gate source voltage, for traditional reference voltage source circuit provides a stable power supply source, make the stability of reference voltage source circuit of the present utility model improve greatly, make that the output of reference voltage source is very little to the sensitivity of supply voltage.

2, circuit of the present utility model can also comprise an anti-power supply dither circuit, and anti-power supply dither circuit plays the effect of filtering on the basis of traditional reference voltage source, has further improved the stability and the anti-power supply shake ability of circuit.

3, the supply voltage pre-adjustment circuit structure that provides of the utility model is simple, only needs a PMOS pipe and a current source, just can be traditional reference voltage source a stable power supply source is provided; Anti-power supply dither circuit only needs an electric capacity just can suppress the influence of the shake of supply voltage to reference voltage source output effectively.

4, reference voltage source circuit wide adaptability of the present utility model goes for multiple traditional reference voltage source circuit, is widely used.

5, the utility model circuit required device has seldom reduced cost greatly.

Description of drawings

Fig. 1 is a circuit structure block diagram of the present utility model.

Fig. 2 is another circuit structure block diagram of the present utility model.

Fig. 3 is the circuit diagram of the utility model first embodiment.

Fig. 4 is the circuit diagram of the utility model second embodiment.

Fig. 5 is the circuit diagram of the utility model the 3rd embodiment.

Embodiment

Below by specific embodiment of the utility model also in conjunction with the accompanying drawings, the purpose of this utility model, circuit structure and advantage are further described.

As Fig. 1, shown in 2, a kind of reference voltage source circuit of the present utility model comprises power supply pre-adjustment circuit 1, reference voltage source circuit 2, power supply pre-adjustment circuit 1 is used to reduce circuit to direct supply change in voltage sensitivity, it can produce a pre-adjustment voltage Vreg, for voltage source circuit 2 provides a stable power supply source, its voltage input end meets power supply Vdd, the pre-adjustment power end connects the input power supply source end of voltage source circuit 2, the reference voltage output end of voltage source circuit 2 connects the pressure feedback port of power supply pre-adjustment circuit 1, and output reference output voltage V ref; On this basis, in order to carry out filtering to output voltage, the filtering garbage signal suppresses the influence of the shake of supply voltage to reference voltage source output effectively, can also add anti-power supply dither circuit 3, its filtering end is connected with the reference voltage output end of voltage source circuit 2.

Above-mentioned power supply pre-adjustment circuit 1 is made up of current source A1 and PMOS pipe M6, the end of current source A1 is the voltage input end of power supply pre-adjustment circuit 1, meet power supply Vdd, the other end is connected with the source electrode of PMOS pipe M6 and links to each other with the input power supply source end of voltage source circuit 2, be and produce pre-adjustment voltage Vreg, the grid of PMOS pipe M6 connects the reference voltage output end of voltage source circuit 2 as the pressure feedback port of power supply pre-adjustment circuit 1, while is input reference output voltage V ref also, and the drain electrode of PMOS pipe M6 connects common.

Above-mentioned anti-power supply dither circuit 3 is made up of capacitor C 1, and an end of capacitor C 1 is connected another termination common as the input end of anti-power supply dither circuit 3 with the reference voltage output end of voltage source circuit 2.

Voltage source circuit 2 is traditional reference voltage source circuit, and Fig. 3, Fig. 4, Fig. 5 have illustrated several embodiment of the present utility model respectively; Voltage source circuit 2 is made up of biasing circuit 21 and reference voltage output circuit 22; Constitute biasing circuit 21 by PMOS pipe M1, M2, M3, M4 and resistance R 1 among Fig. 2, constitute reference voltage output circuit 22 by PMOS pipe M5, resistance R 2 and PNP pipe Q1; Traditional reference voltage source circuit among Fig. 3 is managed M7, M8, M11 by PMOS, NMOS pipe M9 and M10, and resistance R 2, and triode Q1～Q3 composition utilize the temperature characterisitic of triode BE junction voltage to carry out the reference voltage source that temperature compensation formation low temperature floats; Traditional reference voltage source circuit among Fig. 4 is managed M12, M13, M16 by PMOS, and NMOS pipe M14, M15, M17 and resistance R 1 are formed, and utilize the temperature coefficient of NMOS pipe threshold voltage and mobility to form the reference voltage source that low temperature floats.

Behind energized voltage, power supply pre-adjustment circuit 1 is at first worked, for voltage source circuit 2 provides a working power, after voltage source circuit 2 operate as normal, provide benchmark output voltage V ref as feedback voltage to power supply pre-adjustment circuit 1, the stable pre-adjustment voltage of final formation offers voltage source circuit 2, makes the output voltage of reference voltage source have the characteristics of high stability.

Principle of the present utility model is as follows:

Traditional reference voltage source circuit utilizes the subthreshold region saturation current to be the characteristic of exponential relationship with voltage, the positive temperature coefficient (PTC) of the voltage source that generation and absolute temperature are proportional, the negative temperature coefficient of compensation bipolar transistor BE knot pressure drop, thus the less reference voltage source of temperature coefficient obtained.PMOS pipe M3 and M4 require to be operated in subthreshold region among Fig. 3, obtain:

$I_{D3}=I_{o3}\exp \frac{V_{\mathrm{GS}3}}{{\mathrm{\ξV}}_T}$

$I_{D4}=I_{o4}\exp \frac{V_{\mathrm{GS}4}}{\mathrm{\ξ}{V}_T}$

So, $\frac{I_{D3}}{I_{D4}}=\frac{\mathrm{\&beta;}3}{\mathrm{\&beta;}4}\exp \frac{{\mathrm{\&Delta;V}}_{\mathrm{GS}}}{{\mathrm{\&xi;V}}_T}=\frac{\mathrm{\&beta;}3}{\mathrm{\&beta;}4}\mathrm{<figure-callout\; id="1"\; label="exp\; V\; R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">exp</figure-callout>}\frac{V_R}{}\frac{1_{}}{{\mathrm{\&xi;V}}_T}$ Wherein β 3, and β 4 represents the breadth length ratio of M3, M4 pipe, I respectively _DBe leakage current, V _GSBe gate source voltage, ξ is an imperfect factor, V _TIt is thermal voltage.

Again $\frac{I_{D3}}{I_{D4}}=\frac{\mathrm{\&beta;}1}{\mathrm{\&beta;}2}$ Obtain: ${\mathrm{<figure-callout\; id="1"\; label="V\; R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">V</figure-callout>}}_R={\mathrm{\&xi;V}}_T\ln \frac{\mathrm{\&beta;}4\mathrm{\&beta;}2}{\mathrm{\&beta;}3\mathrm{\&beta;}1}$

So, $I_{D5}=\frac{\mathrm{\&beta;}5}{\mathrm{\&beta;}2}{I}_{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">D</figure-callout>}2}=\frac{\mathrm{\&beta;}5}{\mathrm{\&beta;}2}\frac{V_{R1}}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">R</figure-callout>}1}$

So: $V_{\mathrm{ref}}=V_{\mathrm{be}}+{R2I}_{D5}=V_{\mathrm{be}}+\frac{R2}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">R</figure-callout>}1}\frac{\mathrm{\&beta;}5}{\mathrm{\&beta;}2}{\mathrm{\&xi;V}}_T\ln \frac{\mathrm{\&beta;}4\mathrm{\&beta;}2}{\mathrm{\&beta;}3\mathrm{\&beta;}1},$ Wherein, V _RefBe reference voltage source output, V _BeBe the base stage-emitter voltage of triode, V _R1Be the voltage at resistance R 1 two ends.

By the said temperature compensation, can obtain the reference voltage output of low-temperature coefficient.

Power supply pre-adjustment circuit 1 can provide stable power supply source for traditional reference voltage source circuit 2.Current source A1 in the power supply pre-adjustment circuit 1 provides stable electric current I 1.For traditional reference voltage source circuit, electric current is determined by subthreshold region NMOS pipe, also substantially constant, also be steady state value so flow through the electric current of PMOS pipe M6, the electric current I 1 that requires current source A1 to provide when design is greater than the total current of traditional reference voltage source circuit, and both difference electric currents flow through PMOS pipe M6.Know that by the saturation region current formula it is constant that steady current flows through the Vgs that forms behind the PMOS pipe M6.And the grid of PMOS pipe M6 is controlled by benchmark output voltage V ref, source voltage for PMOS pipe M6 is also constant relatively, promptly produced pre-adjustment voltage Vreg,, effectively raised the stability of reference circuit for traditional reference voltage source circuit 2 provides stable power supply source.

Anti-power supply dither circuit 3, the i.e. capacitor C 1 that links to each other with common at reference voltage output end, when benchmark output voltage V ref occurs shaking along with the shake of supply voltage, because the existence of capacitor C 1, AC signal has been carried out Filtering Processing, suppressed the influence of the shake of supply voltage effectively, improved the stability of reference circuit output reference voltage.

Fig. 3 only is a specific embodiment according to the utility model thought, only for the usefulness that the utility model is described, but not to restriction of the present utility model.Person skilled in the relevant technique, under the situation that does not break away from spirit and scope of the present utility model, can also make various conversion and modification, such as changing traditional reference voltage source circuit 2 into the structure different with Fig. 3, so all technical schemes that are equal to also should belong within the category of the present utility model; Such as Fig. 4 and the described reference voltage source circuit of Fig. 5, traditional voltage source circuit difference, but taked same pre-adjustment circuit, reach above-mentioned beneficial effect too.

Among Fig. 4, PNP pipe Q1 is made up of n transistor unit arranged side by side, and PNP pipe Q2 is a transistor unit.Article two, branch current all is I, so:

$\mathrm{\&Delta;}{V}_{\mathrm{BE}}=V_{\mathrm{BE}2}-{\mathrm{<figure-callout\; id="1"\; label="V\; BE"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{BE}}=V_T\ln \frac{I}{I_s}-V_T\ln \frac{I}{{\mathrm{nI}}_s}=V_T\ln n$

Δ V _BE=IR1, thus obtain $I=\frac{{\mathrm{\&Delta;<figure-callout\; id="1"\; label="V\; BE\; R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{BE}}}{R},$ As seen, I is the electric current with positive temperature coefficient (PTC).

Therefore, $\mathrm{Vref}={\mathrm{<figure-callout\; id="2"\; label="V\; BE"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{BE}}+I{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">R</figure-callout>}}_2=V_{\mathrm{<figure-callout\; id="2"\; label="BE"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">BE</figure-callout>}2}+\frac{R2}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">R</figure-callout>}1}\mathrm{\&Delta;}{V}_{\mathrm{BE}}={\mathrm{<figure-callout\; id="2"\; label="V\; BE"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{BE}}+V_T\frac{R2}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">R</figure-callout>}1}\ln n$

$\frac{\&PartialD;\mathrm{Vref}}{\&PartialD;T}=\frac{{\&PartialD;V}_{\mathrm{BE}2}}{\&PartialD;T}+\left(\frac{R2}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">R</figure-callout>}1}\ln n\right)\frac{\&PartialD;V_T}{\&PartialD;T}$

V _BE2Negative temperature coefficient be approximately-2mV/ ℃ V _TPositive temperature coefficient (PTC) be 0.089mV/ ℃, then obtaining zero-temperature coefficient, to compensate needed proportionality constant be 2/0.089 ≈ 22.5, should make when promptly designing

Equal or near 22.5, thereby realize temperature compensation, obtain the reference voltage source circuit that low temperature floats.

Vref＝V _BE+KV _T

PMOS pipe M16, NMOS pipe M17 is the core of reference circuit among Fig. 5, and by PMOS pipe M16 replica current, the gate source voltage Vgs6 of NMOS pipe M17 directly forms the reference voltage of low-temperature coefficient.

$\mathrm{Vref}=\mathrm{Vgs}6=\mathrm{Vth}6\left(T\right)+\sqrt{\frac{{2I}_{M6}}{{\mathrm{\&mu;}}_n\left(T\right)C_{\mathrm{ox}}{\left(\frac{W}{L}\right)}_6}}$

$=\mathrm{Vth}6\left(T_0\right)-\mathrm{\&beta;vth}6(T-T_0)+\frac{2}{{\mathrm{\&mu;}}_n\left(T_0\right)C_{\mathrm{ox}}R1}\left(\frac{1}{\sqrt{{\left(\frac{W}{L}\right)}_3-{\left(\frac{W}{L}\right)}_4}}\right)\sqrt{\frac{M}{{\left(\frac{W}{L}\right)}_6}}{\left(\frac{T}{T_0}\right)}^{\mathrm{\&beta;un}}$

So, $\frac{\&PartialD;\mathrm{Vref}}{\&PartialD;T}=-\mathrm{\&beta;vth}6+\mathrm{\&beta;un}\frac{2}{{\mathrm{\&mu;}}_n\left(T_0\right)C_{\mathrm{ox}}R1}\left(\frac{1}{\sqrt{{\left(\frac{W}{L}\right)}_3-{\left(\frac{W}{L}\right)}_4}}\right)\sqrt{\frac{M}{{\left(\frac{W}{L}\right)}_6}}{\left(\frac{T}{T_0}\right)}^{\mathrm{\&beta;un}-1}$

Order $\frac{\&PartialD;\mathrm{Vref}}{\&PartialD;T}=0,$ Then:

$\frac{M}{{\left(\frac{W}{L}\right)}_6}={\left(\frac{\mathrm{\&beta;vth}6\&CenterDot;{\mathrm{\&mu;}}_n\left(T_0\right){\mathrm{<figure-callout\; id="1"\; label="C\; ox\; R"\; filenames="S2007200433802E00021.png"\; state="\{\{state\}\}">C</figure-callout>}}_{\mathrm{ox}}R1}{2\mathrm{\&beta;un}\&CenterDot;{\left(\frac{T}{T_0}\right)}^{\mathrm{\&beta;un}-1}}\sqrt{{\left(\frac{W}{L}\right)}_3-{\left(\frac{W}{L}\right)}_4}\right)}^2$

Wherein, Vth is a threshold voltage, T ₀Be reference temperature, β vth is the temperature coefficient of threshold voltage, μ _nBe mobility, β un is a mobility temperature coefficient index, C _OxBe the gate oxide electric capacity of unit area.

Can determine relatively that according to following formula M value and NMOS manage the breadth length ratio of M17, suitably regulate the magnitude of voltage that obtains low-temperature coefficient.Suppose that benchmark presents positive temperature coefficient (PTC), then can perhaps reduce NMOS pipe M17 electric current and obtain zero-temperature coefficient by increasing NMOS pipe M17 W/L, on the contrary similar.

Power supply pre-adjustment circuit 1 can provide stable power supply source for voltage source circuit 2.Current source A1 in the power supply pre-adjustment circuit 1 provides stable electric current.For voltage source circuit, electric current is by the decision of PNP pipe, and also substantially constant also is steady state value so flow through the electric current of PMOS pipe M6, the electric current I 1 that requires current source A1 to provide when design is greater than the total current of voltage source circuit, and both difference electric currents flow through PMOS pipe M6.Know that by the saturation region current formula it is constant that steady current flows through the Vgs that forms behind the NMOS pipe M17.And the grid of NMOS pipe M17 is controlled by benchmark output voltage V ref, source voltage for PMOS pipe M6 is also constant relatively, promptly produced pre-adjustment voltage Vreg,, effectively raised the stability of reference circuit for traditional reference voltage source circuit 2 provides stable power supply source.

Claims (4)

1, a kind of reference voltage source circuit, comprise voltage source circuit (2), it is characterized in that: also comprise power supply pre-adjustment circuit (1), the voltage input end of power supply pre-adjustment circuit (1) meets power supply Vdd, its pre-adjustment power end connects the input power supply source end of voltage source circuit (2), the reference voltage output end of voltage source circuit (2) connects the pressure feedback port of power supply pre-adjustment circuit (1), and output reference output voltage V ref.

2, a kind of reference voltage source circuit according to claim 1, it is characterized in that: described power supply pre-adjustment circuit (1) comprises current source A1 and PMOS pipe M6, the end of current source A1 meets power supply Vdd as the voltage input end of power supply pre-adjustment circuit (1), the source electrode of its other end and PMOS pipe M6 is connected and links to each other with the input power supply source end of voltage source circuit (2) as the pre-adjustment power end of power supply pre-adjustment circuit (1), output pre-adjustment voltage Vreg, the grid of PMOS pipe M6 is as the pressure feedback port of power supply pre-adjustment circuit (1), the output voltage signal of input voltage source circuit (2), the drain electrode of PMOS pipe M6 connects common.

3, a kind of reference voltage source circuit according to claim 1 and 2 is characterized in that: also comprise anti-power supply dither circuit (3), the filtering end of anti-power supply dither circuit (3) is connected with the reference voltage output end of voltage source circuit (2).

4, a kind of reference voltage source circuit according to claim 3, it is characterized in that: described anti-power supply dither circuit (3) comprises capacitor C 1, capacitor C 1 one ends are connected another termination common of capacitor C 1 as the filtering end of anti-power supply dither circuit (3) with the reference voltage output end of voltage source circuit (2).

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