CN1208282A - Amplifier noise reducing method and ultralow-noise pre-amplifier - Google Patents

Abstract

Making voltage amplifier fit with input signal source can eliminate noise and specifically the input impedance of signal source is regulated to reach optimal S/N ratio. The ultralow-noise pre-amplifier adopts differential amplifier circuit, the power source is powered by one reference power source module, the output signal is first amplified by two operational amplifiers and then led to the shielding layer, and the signal led to the shielding layer is the same as that in the shielded wire in magnitude and polarity to reduce or even eliminate the effect of distribution capacity. The pre-amplifier has one equivalent input noise lower than 0.11 micron volt and can suit the needs of seismic prospecting and physical prospecting.

Description

A kind of method of step-down amplifier noise and ultra-low noise preamplifier thereof

The present invention relates to amplifying technique, can be used for seismic prospecting, physical prospecting or other needs ultra-low noise to amplify the method and the ultra-low noise preamplifier thereof of a kind of step-down amplifier noise of occasion the electric microfield signal.

Need the high occasion of amplifier signal to noise ratio for seismic prospecting, physical prospecting or other, can the step-down amplifier noise be the key that realize the operation purpose.At present, conventional solution mainly is to improve amplifier itself, but still can not adapt to requirement under some operational environment, the equivalent input noise of the amplifier that generally adopts as distance apparatus is more than 0.15 microvolt, as SYSTEMONE (U.S.'s product) is that 0.23 microvolt, SYSTEMTWO (U.S.'s product) are that 0.157 microvolt, ARAM24 (Canadian product) are 0.2 microvolt, and these products all do not reach the purpose of gathering the following weak electric field signal of 0.12 microvolt.The employed preamplifier of above-mentioned instrument, its structure are difference input, the degenerative amplifier of degree of depth Voltage Series.This differential voltage amplifier only simply consider to improve input impedance, reducing the load to previous stage, and does not consider the influence of the adaptability of signal source characteristic and amplifier itself to equivalent reference noise, starts with and reaches optimum signal-noise ratio from mating input impedance.In addition, amplifier itself is defectiveness also, is to obtain through the discrete component voltage stabilizing from+15V power supply as the required reference power supply of circuit, produces bigger noise, and the passive shielding mode of employing can not effectively be eliminated noise.

The object of the invention is to adopt optimum noise matching technique and active screen fraud technology, and it is following and a kind of method and ultra-low noise preamplifier thereof of step-down amplifier noise be provided to make the equivalent input noise of preamplifier be reduced to 0.11 microvolt.

Description of drawings of the present invention is as follows:

Fig. 1 is that the present invention realizes the designed amplifier model of best input coupling;

Fig. 2 is the circuit theory diagrams of ultra-low noise preamplifier.

The present invention has adopted a kind of method of step-down amplifier noise, make the signal source characteristic of differential voltage amplifier and input adapt to eliminate noise, specifically adjust signal source input impedance and reach optimum signal-noise ratio, calculate the best source resistance corresponding with known amplifier according to following formula: $R=\frac{E_n}{I_n}=\sqrt{\frac{4\mathrm{kT\Δf}+r_{{\mathrm{bb}}^{\′}}+2q{I}_b\mathrm{\Δf}(1+\frac{f_1}{f}){\left(r_{{\mathrm{bb}}^{\′}}\right)}^2+2q{I}_c\mathrm{\Δf}\frac{(r_{{\mathrm{bb}}^{\′}}+r_{b^{\′}e}(1+\mathrm{\β})R_e}{{{\mathrm{\β}}_0}^2}}{2q{I}_b\mathrm{\Δf}(1+\frac{f_1}{f})+\frac{2q{I}_c\mathrm{\Δf}}{{{\mathrm{\β}}_0}^2}}}$

In the formula: r _{Bb '}For differential amplifier base diffusion resistance K is absolute temperature I for Boltzmann constant T _bFor base stage quiescent current q is electron charge I _cF is frequency bandwidth r for collector electrode quiescent current Δ _{B ' e}Be collector region diffusion resistance β ₀Be gm β r _eFor emitter resistance f is operating frequency f ₁For low frequency corner frequency β is the current amplification factor R of Q1 _sBe the signal source internal resistance

According to network theory, the internal noise of an amplifier can be with one that the is connected on input voltage generator E with zero impedance _nWith a current feedback circuit I who is connected in parallel on input with infinite-impedance _nRepresent, claim this noise model that is expressed as, as Fig. 3.

R wherein _sBe signal source internal resistance, E _NsBe the thermal noise in the signal source internal resistance, A _vBe the voltage gain of amplifier, ρ is a coefficient correlation.The expression formula of equivalent input noise is: ${\mathrm{<figure-callout\; id="2"\; label="E\; m"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">E</figure-callout>}}_m^{}=\frac{E_{\mathrm{no}}^2}{{\mathrm{<figure-callout\; id="2"\; label="A\; v"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">A</figure-callout>}}_v^{}}={\mathrm{<figure-callout\; id="2"\; label="E\; ns"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathrm{ns}}^{}+{\mathrm{<figure-callout\; id="2"\; label="E\; n"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">E</figure-callout>}}_n^{}+I_n^2{\mathrm{<figure-callout\; id="2"\; label="R\; s"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">R</figure-callout>}}_s^{}+2\mathrm{\&rho;}{E}_n{I}_n{R}_s$ Noise factor is: $F=\frac{\frac{V_s^2}{E_{\mathrm{ns}}^2}}{\frac{V_{\mathrm{so}}^2}{{\mathrm{<figure-callout\; id="2"\; label="E\; no"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathrm{no}}^{}}}=\frac{{\mathrm{<figure-callout\; id="2"\; label="E\; ns"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathrm{ns}}^{}+{\mathrm{<figure-callout\; id="2"\; label="E\; n"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">E</figure-callout>}}_n^{}+I_n^2{\mathrm{<figure-callout\; id="2"\; label="R\; s"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">R</figure-callout>}}_s^{}+2\mathrm{\&rho;}{E}_n{I}_n{R}_s}{{\mathrm{<figure-callout\; id="2"\; label="E\; ns"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathrm{ns}}^{}}=1+\frac{{\mathrm{<figure-callout\; id="2"\; label="E\; n"\; filenames="A9810188000061.png"\; state="\{\{state\}\}">E</figure-callout>}}_n^{}}{4{\mathrm{KTR}}_s\mathrm{\&Delta;f}}+\frac{I_n}{4\mathrm{KT\&Delta;f}}{R}_s$ This formula is asked local derviation, order

Can obtain the minimal noise coefficient

And optimum source impedance

Press R _SoptModelled signal source (wave detector, electrode etc.) internal resistance is to selected amplifier, E _nAnd I _nAll definite, if coefficient correlation is zero, when then genertor impedance equals optimum source impedance, can obtain the minimal noise coefficient, realize the optimum noise coupling.

The present invention also comprises and the matching used ultra-low noise preamplifier of the method for above-mentioned step-down amplifier noise, amplifier is a differential amplifier circuit, adopt the active shielding circuit, the signal of output is by AR4 and AR5 amplifier, be incorporated on the screen, its signal magnitude and polarity are identical with signal on the shielded wire, can reduce or eliminate the distributed capacitance effect.

Amplifier of the present invention also adopts Ref01 reference power source module for power supply, and reference power source is provided, and further improves signal to noise ratio.

Amplifier of the present invention is formed by three grades, input stage, intergrade and output stage (as Fig. 2).The requirement that should satisfy noise objective, source impedance characteristic, frequency response and conjugated analoging systeming ratio of input stage; The requirement that should satisfy frequency response, voltage gain and inter-stage impedance matching of intergrade; The requirement that should satisfy characteristics of signals conversion, low output impedance and high input impedance of output stage.

Q1 and corresponding device have been formed differential input stage; AR1 and AR2 are single order active filter (integrating circuit), serve as intergrade, and the high-frequency cut-off frequency is 1000HZ; AR3 is an output stage.AR1, AR2, and the equal beauty competition home made O of AR3 P27 low noise operational amplifier; AR4 and AR5 have formed the active shielding circuit; R1, R2, R4, R6 and R7 have formed degree of depth Voltage Series negative-feedback circuit, and resistor network has determined Amplifier Gain, and the size of gain is by S1 switch control, gain for 24dB, 36dB and 48dB third gear optional; R12, C8 and S2 switch have been formed frequency spectrum shaping circuit.

The present invention selects Ref01 (U.S.'s stabilized voltage power supply integrated circuit) reference power source module voltage for referencial use for use, has reduced power supply noise.The present invention also adopts the active shielding skill, improves on incoming line, to add upper shielding layer usually, and the shielding layer grounding method.Because this method makes between screen and holding wire and has distributed capacitance, the distributed capacitance effect can make effective input signal reduce, and phase shifts is arranged.The active shielding technology be with the signal of output by AR4 and AR5 gain, be incorporated on the screen, its signal magnitude and polarity are identical with signal on the conductively-closed holding wire, can reduce or eliminate the distributed capacitance effect, raising efficiency of transmission and signal to noise ratio.

Other technical indicator of amplifier of the present invention is: conjugated analoging systeming ratio is 109 decibels, and distortion is 0.01%, and below equivalent input noise 0.11 microvolt, maximum input signal is 298.125mv, and the frequency band degree is 1300HZ.

Advantage of the present invention is to adopt optimum noise matching technique and active screen fraud technology, and the equivalent input noise of preamplifier is reduced to below 0.11 microvolt, the occasion that the ultra-low noise of can satisfying the demand amplifies.

Claims (3)

1. the method for a step-down amplifier noise, it is characterized in that making the signal source characteristic of differential voltage amplifier and input to adapt to eliminate noise, specifically adjust signal source input impedance and reach optimum signal-noise ratio, calculate the best source resistance corresponding with known amplifier according to following formula: $R=\frac{E_n}{I_n}=\sqrt{\frac{4\mathrm{kT\&Delta;f}+r_{{\mathrm{bb}}^{\&prime;}}+2q{I}_b\mathrm{\&Delta;f}(1+\frac{f_1}{f}){\left(r_{{\mathrm{bb}}^{\&prime;}}\right)}^2+2q{I}_c\mathrm{\&Delta;f}\frac{(r_{{\mathrm{bb}}^{\&prime;}}+r_{b^{\&prime;}e}(1+\mathrm{\&beta;})R_e}{{{\mathrm{\&beta;}}_0}^2}}{2q{I}_b\mathrm{\&Delta;f}(1+\frac{f_1}{f})+\frac{2q{I}_c\mathrm{\&Delta;f}}{{{\mathrm{\&beta;}}_0}^2}}}$ In the formula: r _{Bb '}For differential amplifier base diffusion resistance K is absolute temperature I for Boltzmann constant T _bFor base stage quiescent current q is electron charge I _cF is frequency bandwidth r for collector electrode quiescent current Δ _{B ' e}Be collector region diffusion resistance β ₀Be gm β r _eFor emitter resistance f is operating frequency f ₁For low frequency corner frequency β is the current amplification factor of Q1

2. with the matching used ultra-low noise preamplifier of the described method of claim 1, adopt differential amplifier circuit, it is characterized in that: power unit adopts Ref01 reference power source module for power supply; The signal of output is incorporated on the screen by AR4 and AR5 amplifier, and its signal magnitude and polarity are identical with signal on the shielded wire, reduces or eliminates the distributed capacitance effect, improves signal to noise ratio.

3. ultra-low noise preamplifier according to claim 2 is characterized in that: power unit adopts Ref01 reference power source module that reference power source is provided.

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