Flicker noise in bandgap?

[OMEsystem]

Why bandgap circuit generates high flicker noise? the transistor flicker noise
will be amplified by core circuit of bandgap? Any intutive explanation?

 

[isaacnewton]

Flick noise is significate only in low frequency range.

Why bandgap circuit generates high flicker noise? the transistor flicker noise
will be amplified by core circuit of bandgap? Any intutive explanation?

 

[eesoko]

Unfortunatelly, you can not avoid flicker noise in CMOS design. The source is imperfections in substrate-oxide region which cause random charge trapping and release of electrons. This is intrinsic to MOS transistor design so it can not be fully avoided, but it can be controlled to some point.

In general, reasons for high flicker noise in bandgaps are short transistors and improper bias point in your opamps. Avoid any pinching-off of the transistors (i.e. insure that most of the current does not flow on the surface) and make them bit longer and you should be fine.

 

[OMEsystem]

Avoid any pinching-off of the transistors (i.e. insure that most of the current does not flow on the surface) and make them bit longer and you should be fine.

How to be sure the most current does not flow on the surface? Reduce Vgs-Vth?

 

[wonbef]

the flick noise is inverse proportional to W*L of transistor!

good luck!

 

[eesoko]

I usually do it by decreasing Vds and insuring that Vgb is high. This way I have both Vgs and Vgd relatively high, hence no pinching effect on either side of the channel. Unfortunately, in diode connected transistor you can not play with Vgd, so for current mirrors this will not work. You will have to play with current density.

There could be better ways too.
Good luck.

 

[bkat]

how to simulate fick noise with hspice ?

can supply some example?

thx

 

[Grig]

Hi Bkat
Use AC noise analysis to simulate bandgap noise
You need good cmos and bjt noise model fo freq of interest also

 

[OMEsystem]

I usually do it by decreasing Vds and insuring that Vgb is high. This way I have both Vgs and Vgd relatively high, hence no pinching effect on either side of the channel. Unfortunately, in diode connected transistor you can not play with Vgd, so for current mirrors this will not work. You will have to play with current density.

There could be better ways too.
Good luck.

Thanks for your detailed explanation, would you mind introduce the reference
of it?
thank you,

 

[qiushidaren]

I am also very much interested in this kind of issue.

 

[hoolish]

the normal way to reduce the flicker noise is just increase W*L.

 

[surianova]

the normal way to reduce the flicker noise is just increase W*L.

and put RC filter at the output bandgap will further reduce the output RMS noise across frequency because the noise bandwidth reduce.

 

[caosl]

Add the area of transistor is not a economic method, you can adopt chopper amamp.