# Oversampling technique need help...

Started by September 29, 2011
Hello all,
I have IR preamp with a gain of 64dB, the output noise is about 50mV peak
to peak for a signal of 4V peak peak (max) and the bandwidth is 350kHz.
I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisient for my
aplpication.
I would want to know what would be the best method to filter the noise
(which is white noise and 1/f noise which come from the IR detector) in my
band of interest ...? is it possible ? Does the oversampling could help me
to reduce it ? or does it only improves the quantification noise of the ADC
?
Does it exist another (digital) way to help me to reduce the noise ? Does
the averaging could help me ?

I hope that you could help me.
Regards

On Sep 29, 3:47&#2013266080;am, "glias" <glias37@n_o_s_p_a_m.hotmail.com> wrote:
> Hello all, > I have IR preamp with a gain of 64dB, the output noise is about 50mV peak > to peak for a signal of 4V peak peak (max) and the bandwidth is 350kHz. > I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisient for my > aplpication. > I would want to know what would be the best method to filter the noise > (which is white noise and 1/f noise which come from the IR detector) in my > band of interest ...? is it possible ? Does the oversampling could help me > to reduce it ? or does it only improves the quantification noise of the ADC > ? > Does it exist another (digital) way to help me to reduce the noise ? Does > the averaging could help me ? > > I hope that you could help me. > Regards
The way to approach this problem is to solve for system NF of the system. Once you get that number you can solve for system dynamic range that can be used to calculate the noise floor. No = (KTBGF) F = ((s/n)i)/((s/n)o) The dynamic range of the A/D can be calculated using: 6db*N + 10*log(Fs) &#2013266070; 10*log(Bwa) &#2013266070; 1.25db Where: KT is boltzman constant, B is analog bandwidth, G is amp gain, F is noise figure, N is A/D bits, Fs is sample rate and Bwa is the final analysis bandwidth. So calculate the NF of the amp, NF of the A/D and everything falls out. Regards, Hope this helps
On Thu, 29 Sep 2011 05:47:17 -0500, glias wrote:

> Hello all, > I have IR preamp with a gain of 64dB, the output noise is about 50mV > peak to peak for a signal of 4V peak peak (max) and the bandwidth is > 350kHz. I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisient > for my aplpication. > I would want to know what would be the best method to filter the noise > (which is white noise and 1/f noise which come from the IR detector) in > my band of interest ...? is it possible ? Does the oversampling could > help me to reduce it ? or does it only improves the quantification noise > of the ADC ? > Does it exist another (digital) way to help me to reduce the noise ? > Does the averaging could help me ? > > I hope that you could help me. > Regards
On 9/29/2011 9:31 AM, me0223@yahoo.com wrote:
> On Sep 29, 3:47 am, "glias"<glias37@n_o_s_p_a_m.hotmail.com> wrote: >> Hello all, >> I have IR preamp with a gain of 64dB, the output noise is about 50mV peak >> to peak for a signal of 4V peak peak (max) and the bandwidth is 350kHz. >> I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisient for my >> aplpication. >> I would want to know what would be the best method to filter the noise >> (which is white noise and 1/f noise which come from the IR detector) in my >> band of interest ...? is it possible ? Does the oversampling could help me >> to reduce it ? or does it only improves the quantification noise of the ADC >> ? >> Does it exist another (digital) way to help me to reduce the noise ? Does >> the averaging could help me ? >> >> I hope that you could help me. >> Regards > > > The way to approach this problem is to solve for system NF of the > system. > > Once you get that number you can solve for system dynamic range that > can be used to calculate the noise floor. > > No = (KTBGF) > > F = ((s/n)i)/((s/n)o) > > The dynamic range of the A/D can be calculated using: > > 6db*N + 10*log(Fs) &#2013266070; 10*log(Bwa) &#2013266070; 1.25db > > Where: KT is boltzman constant, B is analog bandwidth, G is amp gain, > F is noise figure, N is A/D bits, Fs is sample rate and Bwa is the > final analysis bandwidth. > > So calculate the NF of the amp, NF of the A/D and everything falls > out. > > Regards, > Hope this helps
Hardly! He asked how to filter. (Not that the question has an answer with the information given.) Jerry -- Engineering is the art of making what you want from things you can get.
On Sep 29, 8:03&#2013266080;am, Jerry Avins <j...@ieee.org> wrote:
> On 9/29/2011 9:31 AM, me0...@yahoo.com wrote: > > > > > > > On Sep 29, 3:47 am, "glias"<glias37@n_o_s_p_a_m.hotmail.com> &#2013266080;wrote: > >> Hello all, > >> I have IR preamp with a gain of 64dB, the output noise is about 50mV peak > >> to peak for a signal of 4V peak peak (max) and the bandwidth is 350kHz. > >> I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisient for my > >> aplpication. > >> I would want to know what would be the best method to filter the noise > >> (which is white noise and 1/f noise which come from the IR detector) in my > >> band of interest ...? is it possible ? Does the oversampling could help me > >> to reduce it ? or does it only improves the quantification noise of the ADC > >> ? > >> Does it exist another (digital) way to help me to reduce the noise ? Does > >> the averaging could help me ? > > >> I hope that you could help me. > >> Regards > > > The way to approach this problem is to solve for system NF of the > > system. > > > Once you get that number you can solve for system dynamic range that > > can be used to calculate the noise floor. > > > No = (KTBGF) > > > F = ((s/n)i)/((s/n)o) > > > The dynamic range of the A/D can be calculated using: > > > 6db*N + 10*log(Fs) 10*log(Bwa) 1.25db > > > Where: KT is boltzman constant, B is analog bandwidth, G is amp gain, > > F is noise figure, N is A/D bits, Fs is sample rate and Bwa is the > > final analysis bandwidth. > > > So calculate the NF of the amp, NF of the A/D and everything falls > > out. > > > Regards, > > Hope this helps > > Hardly! He asked how to filter. (Not that the question has an answer > with the information given.) > > Jerry > -- > Engineering is the art of making what you want from things you can get.- Hide quoted text - > > - Show quoted text -
I have a hard time telling if this is a homework problem or not. I was attempting to stimulate some thought re dynamic range and how he might use the concept of noise to solve his problem. It looks to me like he&#2013266066;s taking a measurement and reading the fuzz on a scope trace. But I don&#2013266066;t know. An interested student would ask where those equations come from and how he could use them to solve his problem. The concept of how to design a gain lineup, whether that be a op-amp and A/D or a downconvert with a A/D behind and solve for noise is all the same. Simple concepts such as where to place that narrowband filter and why elude many. Never did I say that he supplied enough information &#2013266053; but he does have access to the solution. He just needs to know what to solve for.
>> in my band of interest
That's the first question: What is your band of interest. 350k appears to be the upper limit, but what about the low end? It depends on the application. A lowpass filter allows you to throw away samples afterwards without losing information. This is effectively the same as averaging. For example, if your noise were white and you'd keep 500k out of a 5M bandwidth, you'd remove 90 % of the noise => 10 dB improvement. If - you know the signal spectrum - and you know the noise spectrum - and you want to detect, whether or not the signal is received, the optimal solution is a textbook problem. Have a look here: http://en.wikipedia.org/wiki/Matched_filter at "giving us our normalized filter". Build a matched filter, compare the output against a threshold (see here, why: http://en.wikipedia.org/wiki/Neyman%E2%80%93Pearson_lemma) and you're probably done.
On Thu, 29 Sep 2011 08:29:57 -0700, me0223 wrote:

> On Sep 29, 8:03&nbsp;am, Jerry Avins <j...@ieee.org> wrote: >> On 9/29/2011 9:31 AM, me0...@yahoo.com wrote: >> >> >> >> >> >> > On Sep 29, 3:47 am, "glias"<glias37@n_o_s_p_a_m.hotmail.com> &nbsp;wrote: >> >> Hello all, >> >> I have IR preamp with a gain of 64dB, the output noise is about 50mV >> >> peak to peak for a signal of 4V peak peak (max) and the bandwidth is >> >> 350kHz. I have a AD7626 (16 bits 10MSPS ADC) which is largly >> >> suffisient for my aplpication. >> >> I would want to know what would be the best method to filter the >> >> noise (which is white noise and 1/f noise which come from the IR >> >> detector) in my band of interest ...? is it possible ? Does the >> >> oversampling could help me to reduce it ? or does it only improves >> >> the quantification noise of the ADC ? >> >> Does it exist another (digital) way to help me to reduce the noise ? >> >> Does the averaging could help me ? >> >> >> I hope that you could help me. >> >> Regards >> >> > The way to approach this problem is to solve for system NF of the >> > system. >> >> > Once you get that number you can solve for system dynamic range that >> > can be used to calculate the noise floor. >> >> > No = (KTBGF) >> >> > F = ((s/n)i)/((s/n)o) >> >> > The dynamic range of the A/D can be calculated using: >> >> > 6db*N + 10*log(Fs) 10*log(Bwa) 1.25db >> >> > Where: KT is boltzman constant, B is analog bandwidth, G is amp gain, >> > F is noise figure, N is A/D bits, Fs is sample rate and Bwa is the >> > final analysis bandwidth. >> >> > So calculate the NF of the amp, NF of the A/D and everything falls >> > out. >> >> > Regards, >> > Hope this helps >> >> Hardly! He asked how to filter. (Not that the question has an answer >> with the information given.) >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can >> get.- Hide quoted text - >> >> - Show quoted text - > > > I have a hard time telling if this is a homework problem or not.
Usually the homework problems are worded as such: all the information will be there, there will be distracting information included, but clumsily, the cited application will be trivial, far-fetched, generic, or any combination of the above, the level of specificity of things like voltage ranges or processors will be too high for the stage in the project at which you'd be asking the question, etc. In other words, homework questions spoon-feed a problem to the student to test them on the knowledge that he's learning in the class; if you've done real-world problems of that ilk you can generally see the spoon when you read the homework problem. Sometimes posters will do such a good job of condensing a real-world problem down to the essentials that it looks like homework -- then they get jumped on, and have to defend themselves. -- www.wescottdesign.com
>On Sep 29, 8:03=A0am, Jerry Avins <j...@ieee.org> wrote: >> On 9/29/2011 9:31 AM, me0...@yahoo.com wrote: >> >> >> >> >> >> > On Sep 29, 3:47 am, "glias"<glias37@n_o_s_p_a_m.hotmail.com>
=A0wrote:
>> >> Hello all, >> >> I have IR preamp with a gain of 64dB, the output noise is about 50mV
p=
>eak >> >> to peak for a signal of 4V peak peak (max) and the bandwidth is
350kHz=
>. >> >> I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisient for
my
>> >> aplpication. >> >> I would want to know what would be the best method to filter the
noise
>> >> (which is white noise and 1/f noise which come from the IR detector)
i=
>n my >> >> band of interest ...? is it possible ? Does the oversampling could
hel=
>p me >> >> to reduce it ? or does it only improves the quantification noise of
th=
>e ADC >> >> ? >> >> Does it exist another (digital) way to help me to reduce the noise ?
D=
>oes >> >> the averaging could help me ? >> >> >> I hope that you could help me. >> >> Regards >> >> > The way to approach this problem is to solve for system NF of the >> > system. >> >> > Once you get that number you can solve for system dynamic range that >> > can be used to calculate the noise floor. >> >> > No =3D (KTBGF) >> >> > F =3D ((s/n)i)/((s/n)o) >> >> > The dynamic range of the A/D can be calculated using: >> >> > 6db*N + 10*log(Fs) 10*log(Bwa) 1.25db >> >> > Where: KT is boltzman constant, B is analog bandwidth, G is amp gain, >> > F is noise figure, N is A/D bits, Fs is sample rate and Bwa is the >> > final analysis bandwidth. >> >> > So calculate the NF of the amp, NF of the A/D and everything falls >> > out. >> >> > Regards, >> > Hope this helps >> >> Hardly! He asked how to filter. (Not that the question has an answer >> with the information given.) >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get.-
=
>Hide quoted text - >> >> - Show quoted text - > > >I have a hard time telling if this is a homework problem or not. > >I was attempting to stimulate some thought re dynamic range and how he >might use the concept of noise to solve his problem. > >It looks to me like he=92s taking a measurement and reading the fuzz on >a scope trace. But I don=92t know. > >An interested student would ask where those equations come from and >how he could use them to solve his problem. > >The concept of how to design a gain lineup, whether that be a op-amp >and A/D or a downconvert with a A/D behind and solve for noise is all >the same. > >Simple concepts such as where to place that narrowband filter and why >elude many. > >Never did I say that he supplied enough information =85 but he does have >access to the solution. He just needs to know what to solve for. >
Hello all, Thanks a lot for your replies. First, the application is not a homework, it's a real application and a real problem (for me). The bandwidth of the analog front end (bias and pre amp of the detector is have a high pass filter (a simple first order ac coupling) with 1,5Hz for the high pass filter and 350kHz 3rd order Bessel type low pass filter. I'm sorry for the measurement I don't have access to spectrum analyzer so Yes, the measurement of the "noise" is just a reading from a scope. But it gives me an idea. I'm not a specialist and just wanted to know what could be done to reduce my noise (if it is possible). The oversampling technique permit to reduce the noise from the quantification noise from the ADC. (correct me if I'm wrong !). But it doesn't reduce the noise which come from my analog signal chain, isn't it ? I guess that the only solution to my problem is to improve the analog chain .. ? So using the digital filter just permit to reduce the analog filter (anti aliasing) ?
On Thu, 29 Sep 2011 11:29:38 -0500, glias wrote: