CN104320092A - Wideband and low-noise differential application circuit for measuring weak signal - Google Patents

Abstract

The invention relates to a wideband and low-noise differential application circuit for measuring a weak signal. The amplification circuit comprises a first-stage amplification circuit, a second-stage amplification circuit and a third-stage amplification circuit which are sequentially coupled and connected; both the first-stage amplification circuit and the third-stage amplification circuit are proportional differential amplification circuits; the second-stage amplification circuit is a high-pass filter differential amplification circuit; the first-stage amplification circuit comprises a first resistor, a second resistor, a third resistor, a first integrated operation amplifier and a second integrated operation amplifier; the second-stage amplification circuit comprises a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first capacitor, a second capacitor and a third integrated operation amplifier; the third-stage amplification circuit comprises an eighth resistor, a ninth resistor and a fourth integrated operation amplifier. The wideband and low-noise differential application circuit for measuring the weak signal is a wideband and low-noise amplification circuit provided for the shortages of a weak signal output detecting circuit of a marine sensor; the amplification circuit is capable of effectively amplifying nanometer-stage weak signals within the wideband range of 0.1Hz to 10MHz.

Description

A kind of broadband low noise differential amplifier circuit of Weak absorption

Technical field

The present invention relates to a kind of Technique of Weak Signal Detection, in particular to a kind of broadband, low noise differential amplifier circuit of Weak absorption, this circuit can export ground small-signal to electromagnetic type current meter front sensors and effectively amplify, background noise level in the frequency domain that simultaneously also may be used for measuring multiple sensors material.

Background technology

At present, in the research and development of ocean current measurement instrument, electromagnetic type current meter adopts earth magnetic field as exciting field source because of it, and equipment of itself need not design emission source, makes front-end probe comparatively light.Quicker, convenient relative to other ocean current measurement equipment, be suitable for the parameter measurement under multiple marine environment.As document: the article " jettisoning the development of formula ocean current electric field profile instrument " that Zhang Qisheng etc. deliver at " Chinese Journal of Geophysics " 2013 the 56th (11) volume 3699-3707 page, the electric field amplitude produced due to seawater movement cutting earth magnetism place is very faint, precision is receive volt level (nV) at the signal that 1cm/s current meter produces, and noise should not be greater than 50nV.Effective amplification that general preamplifier disturbs without amplifier noise under can not realizing carrying out different frequency to the small-signal of expection.Therefore, a kind of broadband, low noise amplifier circuit of Weak absorption must be made.

At present, thin film of conductive material due to its stable performance, be easy to integrated, noise is lower, the application in sea sensor is more and more extensive.The background noise level of thin film of conductive material is a key parameter of constraint device sensitivity and accuracy of detection, directly determines the signal to noise ratio (S/N) of transducer.As document: Wu Yong etc. roll up at " electronic component and material " article " Of NiCr Alloy Films Resistance device Research of Noise Characteristic " that 55-65 page delivers for 2006 the 25th (1), and the type thin film resistor is under 3mA current condition, and the 1/f noise at 1Hz place is 1 × 10 ^-14v ²/ Hz, being greater than the white noise after 100Hz is 6 × 10 ^-17v ²/ Hz.Therefore, the noise level of a kind of amplifying circuit under corresponding frequencies must be made lower than the background noise of material, effectively could should measure the noise signal of the type thin-film material.

Summary of the invention

There is the shortcoming that frequency band is narrow, noise is high in the testing circuit that the present invention exports small-signal mainly for sea sensor, the amplifying circuit of a kind of broadband, low noise is provided, this amplifying circuit can carry out effective amplification of nanoscale (nV) small-signal in 0.1Hz-10MHz broad frequency range, and self-noise level is lower.

The technical scheme that the present invention takes for the technical problem existed in solution known technology is:

A broadband low noise differential amplifier circuit for Weak absorption, comprising: first order amplifying circuit, second level amplifying circuit and third level amplifying circuit; Above-mentioned three amplifying circuits are of coupled connections successively, and the described first order and third level amplifying circuit are proportional difference amplifying circuit, and described second level amplifying circuit is high-pass filtering differential amplifier circuit; Wherein:

Described first order amplifying circuit comprises the first resistance, the second resistance, the 3rd resistance, the first integrated transporting discharging and the second integrated transporting discharging; Between the positive terminal that described second resistance is connected to the first integrated transporting discharging and exit; Between the negative phase end that described 3rd resistance is connected to the second integrated transporting discharging and exit; Described first resistance is connected between the positive terminal of the first integrated transporting discharging and the negative phase end of the second integrated transporting discharging; The negative phase end of described first integrated transporting discharging is signal input part, the positive terminal ground connection of described second integrated transporting discharging;

Described second level amplifying circuit comprises the 4th resistance, the 5th resistance, the 6th resistance, the 7th resistance, the first electric capacity, the second electric capacity and the 3rd integrated transporting discharging; The exit of described first integrated transporting discharging is connected with the negative phase end of the 3rd integrated transporting discharging by the first electric capacity, the 4th resistance successively; The exit of described second integrated transporting discharging is connected with the positive terminal of the 3rd integrated transporting discharging by the second electric capacity, the 5th resistance successively; Between the negative phase end that described 6th resistance is connected to the 3rd integrated transporting discharging and exit; The positive terminal of described 3rd integrated transporting discharging is by the 7th grounding through resistance;

Described third level amplifying circuit comprises the 8th resistance, the 9th resistance and the 4th integrated transporting discharging; The exit of described 3rd integrated transporting discharging is connected with the positive terminal of the 4th integrated transporting discharging; The negative phase end of described 4th integrated transporting discharging is connected with the exit of the 4th integrated transporting discharging by the 9th resistance; The negative phase end of described 4th integrated transporting discharging is by the 8th grounding through resistance; The exit of described 4th integrated transporting discharging is the output of signal.

The present invention can also adopt following technical measures:

Further: the resistance of described first resistance is 100 Ω, and the second resistance is 500 Ω, the resistance of the 3rd resistance is 500 Ω.

Further: the capacitance of described first electric capacity is 100 μ F, the capacitance of the second electric capacity is 100 μ F, and the resistance of the 4th resistance is 2K Ω, and the resistance of the 5th resistance is 2K Ω, and the resistance of the 6th resistance is 20K Ω, the resistance of the 7th resistance is 20K Ω.

Further: the resistance of described 8th resistance is 1K Ω, the resistance of the 9th resistance is 10K Ω.

Further: described first electric capacity and the 4th resistance form the high pass filter of the 3rd integrated transporting discharging negative phase end, the second electric capacity and the 5th resistance form the high pass filter of the 3rd integrated transporting discharging positive terminal, and the computing formula of described high pass filter is:

$H\left(f\right)=\frac{j2\mathrm{\πf}{R}_4{C}_1}{1+j2\mathrm{\π}{\mathrm{fR}}_5{C}_2},$

Wherein R4 is the resistance of the 4th resistance, and R5 is the resistance of the 5th resistance, and C1 is the capacitance of the first electric capacity, and C2 is the capacitance of the second electric capacity, and f is frequency, and j is the imaginary part unit of plural number, and R4C1=R5C2=0.20 is time constant;

The value of described High Pass Filter Cutoff Frequency fc is 0.80Hz, and computing formula is:

$f_c=\frac{1}{2\mathrm{\π}{R}_4{C}_1}=\frac{1}{2\mathrm{\π}{R}_5{C}_2}.$

Further: be within the scope of 10Hz-10MHz at frequency band, the input white noise power spectral density of described broadband low noise differential amplifier circuit be 3.12 × 10 ^-18v ²/ Hz, when frequency is 1Hz, the input 1/f noise power spectral density of described broadband low noise differential amplifier circuit be 1.35 × 10 ^-17v ²/ Hz; The noise level of described broadband low noise differential amplifier circuit determines primarily of the noise of first order differential amplifier circuit, and its computing formula is:

$e_{n-\mathrm{in}}^2\left(f\right)=[e_{\mathrm{nA}11}^2\left(f\right)+e_{\mathrm{nA}12}^2\left(f\right)+{\left(\frac{{2R}_2}{R_1}\right)}^2\frac{e_{{\mathrm{nR}}_1}^2\left(f\right)}{{(1+\frac{{2R}_2}{R_1})}^2}+\frac{e_{n{R}_2}^2\left(f\right)}{{(1+\frac{{2R}_2}{R_1})}^2}+\frac{e_{n{R}_3}^2\left(f\right)}{{(1+\frac{{2R}_3}{R_1})}^2}],$

Wherein be the voltage noise power spectral density of the first integrated transporting discharging, be the voltage noise power spectral density of the second integrated transporting discharging, be the equivalent voltage power spectral density of the first resistance (R1), be the equivalent voltage power spectral density of the second resistance, it is the equivalent voltage power spectral density of the 3rd resistance; R1 is the resistance of the first resistance, and R2 is the resistance of the second resistance, and R3 is the resistance of the 3rd resistance.

Further: described first integrated transporting discharging, the second integrated transporting discharging, the 3rd integrated transporting discharging, the 4th integrated transporting discharging are the bipolar field effect transistor operational amplifier A D797 of broadband, high-accuracy, Low Drift Temperature, low noise, when frequency is within the scope of 100Hz-10MHz, Power Spectrum of White Noise density is 8.10 × 10 ^-19v ²/ Hz, when frequency is 1Hz, 1/f noise power spectral density is 6.76 × 10 ^-19v ²/ Hz; Described first resistance, the second resistance, the 3rd resistance, the 4th resistance, the 5th resistance, the 6th resistance, the 7th resistance, the 8th resistance, the 9th resistance are close tolerance seal metal film fixed resistor; Described first electric capacity and the second electric capacity are aluminium electrolytic capacitor.

The advantage that the present invention has and good effect are:

1, multiplication factor spectral performance test: this broadband amplifying circuit is 1210 (about 61.66dB) in the value that frequency band range is multiplication factor G in 10Hz-10MHz, in 0.1Hz-10Hz frequency band, multiplication factor also remains on more than 700 times (about 56.90dB).Its filtering performance is very excellent, does not have other factors to disturb multiplication factor.

2, the input noise test that amplifying circuit is total: in 1Hz-10MHz frequency band range, noise is made up of low frequency 1/f noise and high frequency white noise.Be 14.32 × 10 in the 1/f noise power spectral density at 1Hz place ^-18v ²/ Hz, measure error is 2.15 × 10 ^-18v ²/ Hz; Power Spectrum of White Noise density within the scope of 10Hz-10MHz is 3.04 × 10 ^-18v ²/ Hz, measure error is 0.46 × 10 ^-18v ²/ Hz; Consider error amount, noise measurement is all satisfied with circuit noise design load.

3, this broadband, low noise differential amplifier circuit, effectively can amplify volt level (nV) small-signal of receiving of the multi-frequency that electromagnetic type current meter front sensors exports, also can measure background noise level in multiple sensors material frequency domain simultaneously.

Accompanying drawing explanation

Fig. 1 is circuit theory diagrams of the present invention.

Fig. 2 is circuit multiplication factor spectral performance resolution chart in kind.

Fig. 3 is the total input noise resolution chart of circuit in kind.

Embodiment

For summary of the invention of the present invention, Characteristic can be understood further, hereby exemplify following examples, and coordinate accompanying drawing to be described in detail as follows:

Refer to Fig. 1, Fig. 2 and Fig. 3, a kind of broadband low noise differential amplifier circuit of Weak absorption, comprising: first order amplifying circuit, second level amplifying circuit and third level amplifying circuit; Above-mentioned three amplifying circuits are of coupled connections successively, and the described first order and third level amplifying circuit are proportional difference amplifying circuit, and described second level amplifying circuit is high-pass filtering differential amplifier circuit; Wherein:

Described first order amplifying circuit comprises the first resistance R1, the second resistance R2, the 3rd resistance R3, the first integrated transporting discharging AD797-11 and the second integrated transporting discharging AD797-12; Between the positive terminal that described second resistance R2 is connected to the first integrated transporting discharging AD797-11 and exit; Between the negative phase end that described 3rd resistance R3 is connected to the second integrated transporting discharging AD797-12 and exit; Described first resistance R1 is connected between the positive terminal of the first integrated transporting discharging AD797-11 and the negative phase end of the second integrated transporting discharging AD797-12; The negative phase end of described first integrated transporting discharging AD797-11 is signal input part, the positive terminal ground connection of described second integrated transporting discharging AD797-12; The differential amplification multiple of first order amplifying circuit is (1+2R2/R1), and wherein: R1 is the resistance value of the first resistance R1, R2 is the resistance value of the second resistance R2;

Described second level amplifying circuit comprises the 4th resistance R4, the 5th resistance R5, the 6th resistance R6, the 7th resistance R7, the first electric capacity C1, the second electric capacity C2 and the 3rd integrated transporting discharging AD797-21; The exit of described first integrated transporting discharging AD797-11 is connected with the negative phase end of the 3rd integrated transporting discharging AD797-21 by the first electric capacity C1, the 4th resistance R4 successively; The exit of described second integrated transporting discharging AD797-12 is connected with the positive terminal of the 3rd integrated transporting discharging AD797-21 by the second electric capacity C2, the 5th resistance R5 successively; Between the negative phase end that described 6th resistance R6 is connected to the 3rd integrated transporting discharging AD797-21 and exit; The positive terminal of described 3rd integrated transporting discharging AD797-21 is by the 7th grounding through resistance; The differential amplification multiple of the second amplifying circuit is (R7/R5), and wherein: R5 is the resistance value of the 5th resistance R5, R7 is the resistance value of the 7th resistance R7;

Described third level amplifying circuit comprises the 8th resistance R8, the 9th resistance R9 and the 4th integrated transporting discharging AD797-31; The exit of described 3rd integrated transporting discharging AD797-21 is connected with the positive terminal of the 4th integrated transporting discharging AD797-31; The negative phase end of described 4th integrated transporting discharging AD797-31 is connected with the exit of the 4th integrated transporting discharging AD797-31 by the 9th resistance R9; The negative phase end of described 4th integrated transporting discharging AD797-31 is by the 8th resistance R8 ground connection; The exit of described 4th integrated transporting discharging AD797-31 is the output of signal.The differential amplification multiple of the 3rd amplifying circuit is (1+R9/R8), and wherein: R8 is the resistance value of the 8th resistance R8, R9 is the resistance value of the 9th resistance R9;

Total differential amplification multiple of this specific embodiment amplifying circuit is the superposition of three-stage amplifier multiplication factor, and the computing formula of described total magnification is:

$G=(1+\frac{{2R}_2}{R_1})\left(\frac{R_7}{R_5}\right)(1+\frac{R_9}{R_8})$

Wherein: R1 is the resistance value of the first resistance R1, R2 is the resistance value of the second resistance R2; R5 is the resistance value of the 5th resistance R5, and R7 is the resistance value of the 7th resistance R7; R8 is the resistance value of the 8th resistance R8, and R9 is the resistance value of the 9th resistance R9;

In order to ensure the multiplication factor of every grade of differential amplifier circuit close to 10, the resistance of described first resistance R1 is 100 Ω, and the second resistance R2 resistance is 500 Ω, and the resistance of the 3rd resistance R3 is 500 Ω; The capacitance of described first electric capacity C1 is 100 μ F, and the capacitance of the second electric capacity C2 is 100 μ F, and the resistance of the 4th resistance R4 is 2K Ω, and the resistance of the 5th resistance R5 is 2K Ω, and the resistance of the 6th resistance R6 is 20K Ω, the resistance of the 7th resistance R7 is 20K Ω; The resistance of described 8th resistance R8 is 1K Ω, and the resistance of the 9th resistance R9 is 10K Ω.

When frequency band is within the scope of 10Hz-10MHz, the value of the circuit multiplication factor G of this specific embodiment is 1210 (about 61.66dB), when frequency band is in 0.1Hz-10Hz frequency band, multiplication factor also maintains more than 700 times (about 56.90dB), when frequency band is within the scope of 10Hz-10MHz, the Power Spectrum of White Noise density of amplifying circuit is 3.12 × 10 ^-18v ²/ Hz is 1.35 × 10 in the 1/f noise power spectral density of 1Hz place amplifying circuit ^-17v ²/ Hz.

This specific embodiment amplifying circuit is in 0.1Hz-10Hz frequency band, multiplication factor also maintains more than 700 times (about 56.90dB), first electric capacity C1 and the 4th resistance R4 forms the high pass filter of the 3rd integrated transporting discharging AD797-21 negative-phase input signal, second electric capacity C2 and the 5th resistance R5 forms the high pass filter of the 3rd integrated transporting discharging AD797-21 normal phase input end signal, and the computing formula of described high pass filter is:

$H\left(f\right)=\frac{j2\mathrm{\πf}{R}_4{C}_1}{1+j2\mathrm{\π}{\mathrm{fR}}_5{C}_2},$

Wherein R4 is the resistance of the 4th resistance, and R5 is the resistance of the 5th resistance, and C1 is the capacitance of the first electric capacity, and C2 is the capacitance of the second electric capacity, and f is frequency, and j is the imaginary part unit of plural number, and R4C1=R5C2=0.20 is time constant;

The value of described High Pass Filter Cutoff Frequency fc is 0.80Hz, and computing formula is:

$f_c=\frac{1}{2\mathrm{\π}{R}_4{C}_1}=\frac{1}{2\mathrm{\π}{R}_5{C}_2}.$

Be within the scope of 10Hz-10MHz at frequency band, the input white noise power spectral density of described broadband low noise differential amplifier circuit be 3.12 × 10 ^-18v ²/ Hz, when frequency is 1Hz, the input 1/f noise power spectral density of described broadband low noise differential amplifier circuit be 1.35 × 10 ^-17v ²/ Hz; The noise level of described broadband low noise differential amplifier circuit determines primarily of the noise of first order differential amplifier circuit, and its computing formula is:

$e_{n-\mathrm{in}}^2\left(f\right)=[e_{\mathrm{nA}11}^2\left(f\right)+e_{\mathrm{nA}12}^2\left(f\right)+{\left(\frac{{2R}_2}{R_1}\right)}^2\frac{e_{{\mathrm{nR}}_1}^2\left(f\right)}{{(1+\frac{{2R}_2}{R_1})}^2}+\frac{e_{n{R}_2}^2\left(f\right)}{{(1+\frac{{2R}_2}{R_1})}^2}+\frac{e_{n{R}_3}^2\left(f\right)}{{(1+\frac{{2R}_3}{R_1})}^2}],$

Wherein be the voltage noise power spectral density of the first integrated transporting discharging, be the voltage noise power spectral density of the second integrated transporting discharging, be the equivalent voltage power spectral density of the first resistance (R1), be the equivalent voltage power spectral density of the second resistance, it is the equivalent voltage power spectral density of the 3rd resistance; R1 is the resistance of the first resistance, and R2 is the resistance of the second resistance, and R3 is the resistance of the 3rd resistance.

Described first integrated transporting discharging AD797-11, the second integrated transporting discharging AD797-12, the 3rd integrated transporting discharging AD797-21, the 4th integrated transporting discharging AD797-31 are the bipolar field effect transistor operational amplifier A D797 of broadband, high-accuracy, Low Drift Temperature, low noise, when frequency is within the scope of 100Hz-10MHz, Power Spectrum of White Noise density is 8.10 × 10 ^-19v ²/ Hz, when frequency is 1Hz, 1/f noise power spectral density is 6.76 × 10 ^-19v ²/ Hz; Described first resistance R1, the second resistance R2, the 3rd resistance R3, the 4th resistance R4, the 5th resistance R5, the 6th resistance R6, the 7th resistance R7, the 8th resistance R8, the 9th resistance R9 are close tolerance seal metal film fixed resistor; Described first electric capacity C1 and the second electric capacity C2 is aluminium electrolytic capacitor.

Operation principle of the present invention: in amplifying circuit, due to the existence of amplifier, resistor and capacitor element, according to the frequency of input signal, can affect the multiplication factor of circuit.Simultaneously because electronic device self exists noise, the overall noise of circuit equals the superposition of the noise of each device.The major way of circuit design adopts symmetrical multi-level differential amplifying circuit, reduces individual devices to the impact of circuit as far as possible.Adopt the integrated transporting discharging chip of broadband, low noise in addition, approximate the three-stage amplifier of 10 in conjunction with every grade of multiplication factor, thus ensure that circuit reaches 10 in the multiplication factor of broad frequency band ³doubly.Add two identical symmetrical electric capacity (i.e. the first electric capacity C1, the second electric capacity C2) in circuit design, eliminated the interference of input direct voltage to amplifying circuit by the filtering to low frequency signal.

As shown in Figure 2, amplifying circuit of the present invention is connected to bias voltage source, the swept-frequency signal produced by signal generator is inputted by input.Signalization generator output amplitude is 2mV, and swept-frequency signal scope is 0.1Hz-10MHz.Signal aspects by signal output part obtains: amplifying circuit of the present invention is 1210 (about 61.66dB) in the value that frequency band range is multiplication factor G in 10Hz-10MHz, in 0.1Hz-10Hz frequency band, amplify differential amplification multiple and also remain on more than 700 times (about 56.90dB).Its filtering performance is very excellent, does not have other factors to disturb multiplication factor.

As shown in Figure 3, amplifying circuit of the present invention is connected to bias voltage source, in order to avoid other noise jamming, signal input part ground connection, use spectrum analyzer to test the output voltage noise power of circuit in 1Hz-10MHz frequency range, the waveform obtained after testing square is amplified the total input noise waveform of circuit again divided by the multiplication factor in 1Hz-10MHz frequency band.

Claims (7)

1. a broadband low noise differential amplifier circuit for Weak absorption, is characterized in that: comprising: first order amplifying circuit, second level amplifying circuit and third level amplifying circuit; Above-mentioned three amplifying circuits are of coupled connections successively, and the described first order and third level amplifying circuit are proportional difference amplifying circuit, and described second level amplifying circuit is high-pass filtering differential amplifier circuit; Wherein:

Described first order amplifying circuit comprises the first resistance, the second resistance, the 3rd resistance, the first integrated transporting discharging and the second integrated transporting discharging; Between the positive terminal that described second resistance is connected to the first integrated transporting discharging and exit; Between the negative phase end that described 3rd resistance is connected to the second integrated transporting discharging and exit; Described first resistance is connected between the positive terminal of the first integrated transporting discharging and the negative phase end of the second integrated transporting discharging; The negative phase end of described first integrated transporting discharging is signal input part, the positive terminal ground connection of described second integrated transporting discharging;

Described second level amplifying circuit comprises the 4th resistance, the 5th resistance, the 6th resistance, the 7th resistance, the first electric capacity, the second electric capacity and the 3rd integrated transporting discharging; The exit of described first integrated transporting discharging is connected with the negative phase end of the 3rd integrated transporting discharging by the first electric capacity, the 4th resistance successively; The exit of described second integrated transporting discharging is connected with the positive terminal of the 3rd integrated transporting discharging by the second electric capacity, the 5th resistance successively; Between the negative phase end that described 6th resistance is connected to the 3rd integrated transporting discharging and exit; The positive terminal of described 3rd integrated transporting discharging is by the 7th grounding through resistance;

Described third level amplifying circuit comprises the 8th resistance, the 9th resistance and the 4th integrated transporting discharging; The exit of described 3rd integrated transporting discharging is connected with the positive terminal of the 4th integrated transporting discharging; The negative phase end of described 4th integrated transporting discharging is connected with the exit of the 4th integrated transporting discharging by the 9th resistance; The negative phase end of described 4th integrated transporting discharging is by the 8th grounding through resistance; The exit of described 4th integrated transporting discharging is the output of signal.

2. the broadband low noise differential amplifier circuit of Weak absorption according to claim 1, it is characterized in that: the resistance of described first resistance is 100 Ω, and the second resistance is 500 Ω, the resistance of the 3rd resistance is 500 Ω.

3. the broadband low noise differential amplifier circuit of Weak absorption according to claim 2, it is characterized in that: the capacitance of described first electric capacity is 100 μ F, the capacitance of the second electric capacity is 100 μ F, the resistance of the 4th resistance is 2K Ω, the resistance of the 5th resistance is 2K Ω, and the resistance of the 6th resistance is 20K Ω, the resistance of the 7th resistance is 20K Ω.

4. the broadband low noise differential amplifier circuit of Weak absorption according to claim 3, it is characterized in that: the resistance of described 8th resistance is 1K Ω, the resistance of the 9th resistance is 10K Ω.

5. the broadband low noise differential amplifier circuit of Weak absorption according to claim 4, it is characterized in that: described first electric capacity and the 4th resistance form the high pass filter of the 3rd integrated transporting discharging negative phase end, second electric capacity and the 5th resistance form the high pass filter of the 3rd integrated transporting discharging positive terminal, and the computing formula of described high pass filter is:

$H\left(f\right)=\frac{j2\mathrm{\πf}{R}_4{C}_1}{1+j2\mathrm{\πf}{R}_5{C}_2},$

Wherein R4 is the resistance of the 4th resistance, and R5 is the resistance of the 5th resistance, and C1 is the capacitance of the first electric capacity, and C2 is the capacitance of the second electric capacity, and f is frequency, and j is the imaginary part unit of plural number, and R4C1=R5C2=0.20 is time constant;

The value of described High Pass Filter Cutoff Frequency fc is 0.80Hz, and computing formula is:

$f_c=\frac{1}{2\mathrm{\π}{R}_4{C}_1}=\frac{1}{2\mathrm{\π}{R}_5{C}_2}.$

6. the broadband low noise differential amplifier circuit of Weak absorption according to claim 5, is characterized in that: be within the scope of 10Hz-10MHz at frequency band, the input white noise power spectral density of described broadband low noise differential amplifier circuit be 3.12 × 10 ^-18v ²/ Hz, when frequency is 1Hz, the input 1/f noise power spectral density of described broadband low noise differential amplifier circuit be 1.35 × 10 ^-17v ²/ Hz; The noise level of described broadband low noise differential amplifier circuit determines primarily of the noise of first order differential amplifier circuit, and its computing formula is:

$e_{n-\mathrm{in}}^2\left(f\right)=[e_{\mathrm{nA}11}^2\left(f\right)+e_{\mathrm{nA}12}^2\left(f\right)+{\left(\frac{2R_2}{R_1}\right)}^2\frac{e_{n{R}_1}^2\left(f\right)}{{(1+\frac{2R_2}{R_1})}^2}+\frac{e_{n{R}_2}^2\left(f\right)}{{(1+\frac{2R_2}{R_1})}^2}+\frac{e_{n{R}_3}^2\left(f\right)}{{(1+\frac{2R_3}{R_1})}^2}],$

Wherein be the voltage noise power spectral density of the first integrated transporting discharging, be the voltage noise power spectral density of the second integrated transporting discharging, be the equivalent voltage power spectral density of the first resistance (R1), be the equivalent voltage power spectral density of the second resistance, it is the equivalent voltage power spectral density of the 3rd resistance; R1 is the resistance of the first resistance, and R2 is the resistance of the second resistance, and R3 is the resistance of the 3rd resistance.

7. the broadband low noise differential amplifier circuit of Weak absorption according to claim 6, it is characterized in that: described first integrated transporting discharging, the second integrated transporting discharging, the 3rd integrated transporting discharging, the 4th integrated transporting discharging are the bipolar field effect transistor operational amplifier A D797 of broadband, high-accuracy, Low Drift Temperature, low noise, when frequency is within the scope of 100Hz-10MHz, Power Spectrum of White Noise density is 8.10 × 10 ^-19v ²/ Hz, when frequency is 1Hz, 1/f noise power spectral density is 6.76 × 10 ^-19v ²/ Hz; Described first resistance, the second resistance, the 3rd resistance, the 4th resistance, the 5th resistance, the 6th resistance, the 7th resistance, the 8th resistance, the 9th resistance are close tolerance seal metal film fixed resistor; Described first electric capacity and the second electric capacity are aluminium electrolytic capacitor.