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analog_wiz Junior Member Offline Posts: 31 Universe	Re: How to reduce 1/f noise in BandGap Reply #15 - Nov 30^th, 2012, 12:26am You can also use on chip RC (Small area no external components) filters to filter out the noise.
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loose-electron

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Re: How to reduce 1/f noise in BandGap
Reply #16 - Nov 30^th, 2012, 1:39pm

analog_wiz wrote on Nov 30^th, 2012, 12:26am:

You can also use on chip RC (Small area no external components) filters to

filter out the noise.

Flicker noise is generally DC and near DC,
so filtering does not get you much other than limiting the BW a bit.

Google and IEEE Explore will be your research sources.

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analog_wiz Junior Member Offline Posts: 31 Universe	Re: How to reduce 1/f noise in BandGap Reply #17 - Nov 30^th, 2012, 7:37pm To Optimize a BG for noise will include reducing both (thermal as well as flicker). You can use (on chip rc using special techniques) to get cutoffs as low as 500hz(3db).Loose electron, have you used any other techniques other than those discussed here.
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RobG

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Re: How to reduce 1/f noise in BandGap
Reply #18 - Nov 30^th, 2012, 7:44pm

analog_wiz wrote on Nov 30^th, 2012, 7:37pm:

To Optimize a BG for noise will include reducing both (thermal as well as flicker). You can use (on chip rc using special techniques) to get cutoffs as low as 500hz(3db).Loose electron, have you used any other techniques other than those discussed here.

The original poster was concerned with bandwidths less than 20 Hz. To do that your options are pretty much larger devices, correlated double sampling or chopping.

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analog_wiz Junior Member Offline Posts: 31 Universe	Re: How to reduce 1/f noise in BandGap Reply #19 - Nov 30^th, 2012, 8:26pm OK Robg. Thanks for getting me back to the topic. Also do you have any no's for integrated noise for frequencies upto 10k with chopping.what kind of applications will need that kind of low noise from bandgap.high resolution adc's?
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RobG

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Re: How to reduce 1/f noise in BandGap
Reply #20 - Nov 30^th, 2012, 8:56pm

analog_wiz wrote on Nov 30^th, 2012, 8:26pm:

OK Robg. Thanks for getting me back to the topic. Also do you have any no's for integrated noise for frequencies upto 10k with chopping.what kind of applications will need that kind of low noise from bandgap.high resolution adc's?

Sorry, I don't have any numbers off the top of my head.

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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: How to reduce 1/f noise in BandGap Reply #21 - Dec 1^st, 2012, 1:08am hello all, please the following website papers, you get real numbers and current state of art. http://wwwetis.et.tudelft.nl/people/biography/projectleaders/makinwa_kofi/public... Thanks, Raj.
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loose-electron

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Re: How to reduce 1/f noise in BandGap
Reply #22 - Dec 1^st, 2012, 3:58pm

analog_wiz wrote on Nov 30^th, 2012, 7:37pm:

To Optimize a BG for noise will include reducing both (thermal as well as flicker). You can use (on chip rc using special techniques) to get cutoffs as low as 500hz(3db).Loose electron, have you used any other techniques other than those discussed here.

After you got a BG adjusted where you wanted (curvature correction, offsets and all that)

To the best of my knowledge you got:

Bigger W & L for lower flicker

Lower impedance, higher currents for lower White-thermal-johnson noise.

Chopping to up-convert the near DC noise flicker noise

Bipolar design to get away from MOS flicker noise. (reminder - BJT
devices have flicker noise as well, just orders of magnitude
smaller than MOS devices)

Filtering output

Filtering select nodes in the BG

That's what I am aware of.

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Jerry Twomey
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Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

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Kevin Aylward Community Member Offline Posts: 52	Re: How to reduce 1/f noise in BandGap Reply #23 - Jul 6^th, 2013, 7:44am Use a process with a half decent bipolar. This incessant drive for cmos only is pretty much daft. Many �cmos� processes actually do have a decent bipolar. Just avoid those silly 45nm ones. Who wants to do analog with a few atoms of silicon anyway�
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Venky_analog Junior Member Offline Analog Design is my trade. Math is my love. Posts: 10 TX, USA	Re: How to reduce 1/f noise in BandGap Reply #24 - Feb 3^rd, 2016, 6:23pm Hi, I have a question here. How can source degeneration reduce flicker noise? If it's because of the reduction in the 'gm' of the transistor, then isn't it going to affect the signal by the same amount, thereby keeping the SNR the same?
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RobG

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Re: How to reduce 1/f noise in BandGap
Reply #25 - Feb 3^rd, 2016, 8:02pm

Venky_analog wrote on Feb 3^rd, 2016, 6:23pm:

Hi,

I have a question here. How can source degeneration reduce flicker noise? If it's because of the reduction in the 'gm' of the transistor, then isn't it going to affect the signal by the same amount, thereby keeping the SNR the same?

In this case it is a current mirror that doesn't have a signal - just noise.

In general, for a given DC current, the larger the gate voltage, the lower the noise. So start out with the assumption that we have made the gate voltage as large as headroom will allow. There are two ways you can get this large gate voltage:
1) Small W, large L (gives a large Vgs-Vt)
2) Large W, small L and resistive degeneration

If the total W*L is the same for both cases then (2) will have less 1/f noise current because its gm is less.

The optimum for noise would be to use a really wide device with minimum length, however, that maximizes drain capacitance and minimizes output impedance so there is a trade-off.

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DanielLam

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Re: How to reduce 1/f noise in BandGap
Reply #26 - Feb 5^th, 2016, 12:40pm

Venky_analog wrote on Feb 3^rd, 2016, 6:23pm:

Hi,

I have a question here. How can source degeneration reduce flicker noise? If it's because of the reduction in the 'gm' of the transistor, then isn't it going to affect the signal by the same amount, thereby keeping the SNR the same?

Source degeneration can reduce both flicker and thermal noise (and any other noise produced by that transistor). First, you must understand why the noise of a cascode does not matter much. Then apply this thinking to the source degeneration case. They are very similar, just one has a degeneration resistor instead of a degeneration ro.

Assume there is a noise source at the input of the cascode, what happens to its gain as you increase the source impedance/resistance?

The cascode case is described in Razavi's book in the noise chapter.

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