The element that brings about noise generation may be amplifier circuit itself, the likelihood is the cell that uses in road of its feedback annulus, also may be power source; Noise is likely also from around (or further place) noise source lotus root closes or the response reachs input, output, ground loop or measure circuit in.

 

Undoubted, we depend on to the attention degree of noise at 2 o’clock:

 

● circuit is in target frequency paragraph the resolution; that place should achieve

● avoids noise move to come be not direct and relevant frequency paragraph.

 

Because operation amplifier is multi-purpose,make preamplifier and processor of high accuracy signal, the precision of operation amplifier circuit is paid close attention to increasingly. So we talk today [noise and operation amplifier circuit] .

 

From the point of noise angle, operation amplifier has distinct advantage, apply to low pressure and high accuracy circuit completely, because:

 

● can choose specific amplifier transfer function, make its allow target frequency only paragraph through.

● can choose to get used to the amplifier of specific need from inside the numerous type that has different noise character, so that be in target frequency paragraph inside acquire approximately good character.

● if noise source is foregone and the course is evaluated correctly, the noise condition that can forecast all sorts of amplifier circuit achieves enough precision, provide a basis for abecedarian handiwork design thereby, have the possibility of certain successful test and verify.

 

Basic model one by one voltage noise and voltaic noise

 

Can distinguish difference what operation amplifier regards ideal as not to have noise amplifier, its noise current source is located in each input to bring foot and in all between modular ground, noise voltage source inputs the series connection that cite a base actually with some side. This model and maladjusted analysis 2 useful the E that arrive_OSOne I_BiasThe model is very similar, this is no wonder, because but E_OSWith I_BiasRegard dc noise as the source, can undertake modulation by the parameter such as time, temperature.

 

Graph 1. Voltage and voltaic noise model

 

In most and actual applying, can regard noise voltage source and noise current source as each other independence. If temporary oversight circuit is mixed the dynamic limits element of amplifier, be like E_OSWith I_BiasSame, the instantaneous voltage heft of noise can undertake metrical through circuit of low impedance, tall gain (graph 2) , and heft of instantaneous electric current can be in very big (ideal “ undertakes metrical in the ”) resistor without noise. If E_NWith I_NInteract is not had between, criterion noise voltage is measured output general and (1 + R₂/ R₁) into scale, and noise electric current measures output criterion only with R₂Into scale.

 

Ask an attention, the instantaneous of these two kinds of noise and (appear at amplifier to output end) for

 

 

And when the following equality holds water, E_NWith I_Nopposite noise contribution is equal

 

 

Namely the condition is: R₂With R₁paralell connection is equal to E_NWith I_Nthan. When E of impedance level prep above_N/ I_NWhen, voltaic noise holds dominant. E_NWith I_NOf mean effective value the ” of resistor of “ feature noise that than be being called sometimes amplifier issues in established bandwidth, can regard as when choice and the amplifier that established impedance matchs economic quality factor, vice versa.

 

Graph 2.  E_NWith I_Nmeasure a way basically (need to use filter in tape and sound measurement of dot a confusion of voices)

 

Below the circumstance of foregone voltage and impedance, can regard the noise that closes to cite a base to amplifier input from exterior source lotus root as the voltage of add sex signal, or depend on when the generation of this kind of signal of amplifier when some kind measures way, also can regard add sex electric current as signal, brief show for the graph 3.

 

Graph 3. The contribution of interior and exterior noise source

 

Noise gain and signal gain

 

The graph shows the basic feedback model that returns photograph amplifier for a kind 4 times, contain input of several block sex to cite a base among them. Be worth to bigger annulus road gain (Aβ ) , the noise gain of voltage noise is 1/β actually.

 

Graph 1. Voltage and voltaic noise model

 

If Aβ is not outclass unit gain, can make in order to issues more accurate expression

 

 

corresponding voltaic noise expression is

 

 

Those who need an attention is, to passive feedback component, 1/β won’t be less than unit gain value, and input signal to random, this value also is more than closed circuit gain. Accordingly, although signal gain is less than unit gain, or signal bandwidth is narrower, but the total spectrum of En will appear in output to carry, its value is equal to unit gain at least.

 

Need to notice at the same time, usually, when A all is dynamic expression with β , if the phase shift of annulus road gain is certain the prep above on degree 900, criterion the frequency limits when amplifier is close to Aβ=1 is in owe damp state, criterion the peak value of the noise gain below this frequency is potential gain of prep above unit is very much, although signal gain is when inferior frequency,meet flowing boil fall. Graph 5 for a kind of simple palpability, give typical examples that understands easily.

 

Graph 5. Noise bandwidth and signal bandwidth

 

How token noise

 

Periodic repeat noise to be able to be based on returning rate, weaveform and extent to have picture (the wave that be like behead implement noise) . Irregular noise can pass its weaveform and extent to have picture only, because its change does not have the rule but character (going up somehow for, popcorn noise belongs to this kind) . Those who do not have repeatability weaveform is aperiodic sexual noise passes its statistic character to have a description commonly: Mean effective value, peak value and frequency composition.

 

Mean effective value. Is most and random noise put in the following and characteristic: ? Does  of arrogant of Quan  earnest guide Mei of  of Mao of  of ぃ of mill of tiny stream Cao falls does firewood of smile of paddy of  of wooden  reef wash Shan to look Ge of R of bath of Shao thoroughfaring green makes fun of  to jump  to pound ɑ  to censure  of reef of  of a stone needle used in acupuncture in ancient China of  of Beng of where collate of Mei of Shan of mill ぜ tiny stream hydroxide?

 

 

Among them

 

E_RmsVoltage of = root mean square is worth

T= observation time-interval

Voltage of E= instantaneous noise

 

Among them parameter is replaced be worth I for instantaneous electric current, get I_Rms, namely value of electric current of root mean square. When undertaking root mean square is measured, must use metric instrument of ” of “ true root mean square, also but will communicate average (calibration of sine wave root mean square metric appearance) reading is multiplied with factor 1.13.

 

Peak value. Noise also but what token observes for aleatoric interval is the biggest the difference of extent and the biggest negative range. In certain applying, when noise of peak peak value the likelihood restricts systematic performance when, the likelihood needs to use summit summit to measure a way.

 

However, from the point of pragmatic point of view, because noise amplitude distribution shows gauss to distributing, the probability lowest because of this highest noise extent (but do not be 0) , repeat hard measure noise of the peak value that get a summit. Because mean effective value repeats easily,measure, and it is noise data is accepted, the most commonly used expression means, because this can use estimation issueing a list to be below the case that gives root mean square, exceed the probability of all sorts of peak value.

 

 

The value of summit summit noise that common observation reachs is between 3 X RMS and 8 X RMS, depend on the observer’s patience and available data quantity. Below higher intensity ability observation arrives the trace of oscillograph, because a large number of average evaluation operation are,finish in low intensity however, generation right now one is close to the result of mean effective value relatively. Additional, the analyzer of peak value amplitude distribution that is used at measuring this kind of parameter automatically on the market also increasingly grow in quantity.

 

Disturb noise and inherent noise

 

The noise of established circuit can be divided for two basic categories, disturb noise namely (point to from circuit the noise of exterior collect) with inherent noise (the noise) that shows circuit interior arises.

 

Interference noise may be had periodic, the likelihood is irregular repeat, likely also and complete random, pass the following precautionary measures, often can decrease considerably (or prevent) this kind of noise. For instance, the electromagnetism interference that adopts precautionary measures to be aimed at the place such as the electricity that by frequency of power supply cord and harmonic, radiobroadcast the switch in electric arc of station, mechanical switch and block sex circuit brings or voltage aiguille to cause undertakes ameliorative. This kind of precautionary measures includes filter wave, go lotus root, right down-lead and component undertake electrostatic with electromagnetism screen, use defend potential, eliminate ground annulus road, right down-lead and component position direction discharge cloth afresh, encircle in afterwards electrical wiring medium use damp diode, choose as far as possible low. The interference noise that vibration causes can pass mechanical design improvement. Graph 6 medium form listed the part violates noise source, its pattern value and processing means.

 

Graph 6. Violate noise source typically

 

However, although all interference noise all gets elimination, still put in inherent noise. Inherent noise belongs to random noise substantially normally, appear in resistor and semiconductor component more, wait like transistor and diode. (an example that is not random and inherent noise is behead wave implement the behead wave in stabilized voltage amplifier implement noise. ) the random noise of the generation in resistor component is called to make an appointment with writing abdicate noise (also weigh thermal noise) . The random noise of the generation in semiconductor component may belong to the following 3 kinds one of: Noise of Xiao Te radical (or say to come loose a noise) , twinkle noise (1/f noise) with popcorn noise.