How to reduce the noise in BJT and FET?

[zhi_yi]

hi there, please help me

i read a book, it said that noise occurs in BJT are thermal noise, shot noise, partition noise, flicker noise, and the burst noise, and then, noise occurs in the FETs are thermal noise, flicker noise, and shot noise. my question is how to reduce those noise??

En² = 4.R.k.T.Bn, k is boltzmann constant, how did mister boltzmann find the value for the constanta?

thank you very much

 

[seadolphine2000]

reduce the noise

In any circuit, i you want to reduce noise, then you have to place a filter circuit.
The more the quality of filter, the smaller the noise level.

 

[philipwang]

Re: reduce the noise

Dear Zhi_yi,

Low noise design is a important area in analog design. For example, to lower the 1/f noise in amplifier design ,you should select appropriate transistor type and circuit topology, generally PMOS is better than NMOS, the gain of first-stage should be large if possible, the length of load transistors should longer than that of input pair transistors, etc.

There are many books and papers you can refer, if you are interesting in it, just enjoy it.

Bg,

 

[zhi_yi]

Re: reduce the noise

okay, thank you all, what kind of filter?
in the pre-amp stage, we pass the signal into many stage of filter, HPF, LPF, BPF, my question is in the pre-amp stage, we use LPF to pass the low frequency signal, why it don't produce the noise? the flicker noise and the burst noise? and there are a lot of resistor in the pre-amp stage, why it don't produce a lot of thermal noise? and in the HPF, the passed signal would be in high frequency, it would make the shot noise into the calculation, so it also produce noise in the pre-amp stage, please help me

 

[sisc1525]

reduce the noise

mr. wang's answer is very useful for us.

 

[pseudockb]

Re: reduce the noise

Hi, there are some techniques that can be used to reduce flicker noise of opamp. For example, autozeroing, correlated double sampling and chopper stablization techniques.

 

[archiees]

Re: reduce the noise

Besides using circuit design techniques for low noise application such as source impedance matching, you can reduce thermal noise in the preamps by cooling the circuit itself. People have used dry ice and also liquid helium to aprox. 4 K. But then you have to select the active devices accordingly as silicon cannot be used at such temperatures. GaAs HEMTs do work and are used for low noise amplifications at low temperatures.

 

[xwcwc1234]

Re: reduce the noise

How to simulate the noise performance using Hspice ? When I run transient analysis in Hspice , can I view the noise from the waveform ?

 

[zhi_yi]

Re: reduce the noise

Low noise design is a important area in analog design. For example, to lower the 1/f noise in amplifier design ,you should select appropriate transistor type and circuit topology, generally PMOS is better than NMOS <-- please tell me some of appropriate transistor type what is mean by topology?

Hi, there are some techniques that can be used to reduce flicker noise of opamp. For example, autozeroing, correlated double sampling and chopper stablization techniques. <-- what is autozeroing, correlated double sampling and chopper stabilization techniques? is there a good tutorial about these reduce the flicker noise techniques?

impedance matching could reduce the thermal noise, because of the input impedance from impedance matching circuit is high enough to make the thermal noise from previous stage to be ignored, is it true? if it is true, how about the thermal noise generated from the input impedance it self?

People have used dry ice and also liquid helium to aprox. 4 K. <-- where to buy a liquid helium? what is the physical of liquid helium looks like?

How to simulate the noise performance using Hspice ? When I run transient analysis in Hspice , can I view the noise from the waveform ? <-- what is Hspice? is it a software for simulate the circuit design like multisim?

in the pre-amplifier stage, we always filter the signal and it said the purpose is to manage many kind of sound like bass, treble, midrange, and also to reduce the noise, is it right? if it is true, my question is, when we use low pass filter for bass, the passed signal would be the low frequencies, will it produces flicker noise and burst noise? if it produces the noise, the noise signal and the audio signal would go through the power amplifier and the noise signal and audio signal would be amplified, so the sound produces would be have some noise, is it true? and in the high pass filter, would it make the shot noise influence the output signal?

thank you very much all

 

[microstorm]

Re: reduce the noise

I have readed some papers about this issue, but most of them are concentrated on high frequency circuit, i.e., RF circuit. When it comes to low frequency, I kown to optimize the noise by PMOS input stage, large-gm input FETs, and small-gm load FETs. But what i eager to know is that is there any more about it in linear circuit design?

 

[sarit_g_t]

Re: reduce the noise

The effects of noise also depend on the kind of circuit one is making. For example, 1/f noise etc. are not signivficant when one is designing amplifiers in the Gigahertz range in modern technologies.