On 29-09-2011 at 12:47:17 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 > ?It could help. Do calculation (http://www.dsprelated.com/showmessage/119044/1.php or look for /AD_MT_Tutorial.pdf). Where is the noise, that is the question?> Does it exist another (digital) way to help me to reduce the noise ?Yes, it is digital filter.> Does the averaging could help me ?Yes, averaging is a "digital filter". -- Mikolaj
Oversampling technique need help...
Started by ●September 29, 2011
Reply by ●September 30, 20112011-09-30
Reply by ●September 30, 20112011-09-30
On Thu, 29 Sep 2011 11:11:19 -0700, me0223 wrote:> On Sep 29, 10:41 am, Tim Wescott <t...@seemywebsite.com> wrote: >> On Thu, 29 Sep 2011 11:29:38 -0500, glias wrote: >> >>On Sep 29, 8:03=A0am, Jerry Avins <j...@ieee.org> wrote: >> >>> On 9/29/2011 9:31 AM, me0...@yahoo.com wrote:** snip **>> > So using the digital filter just permit to reduce the analog filter >> > (anti aliasing) ? >> >> Using a filter in digital-land offers a multitude of advantages, about >> the only thing it _doesn't_ do is undo the effects of aliasing -- that >> would be like a blender that can un-scramble eggs. >> >> --www.wescottdesign.com- Hide quoted text - >> >> - Show quoted text - > > > Which topology are you using: > Sensor--->Filter--->op-amp--->A/D > or > Sensor---> Op-Amp--->Filter--->A/D > > For any amp string the noise performance of the system, i.e., the noise > floor will be set by the first amp. It can never be better than that. > Another way to say it is, if you create noise in your amp string, you > can’t see a signal from your input source better than that. > > Any lossy components, (i.e. resistors, non-ideal filters), in front of > an amplifier adds to the noise. > You will never be able to see below the noise floor set by your system > NF. > > What process gain and averaging allow you to do, is get down to the > noise floor of your gain chain. So you want your narrowest filter to be > the digital filter. Noise Out of your gain stage = KTBGF. Consider your > A/D as just another gain stage with a NF.The only quirk with thinking of the A/D as just another gain stage with a NF is that the NF changes with sampling rate -- the noise power never changes, but sampling faster spreads that noise power out (or scrunches up the spectrum of the desired signal, depending on whether you're looking at things from inside or outside the sampled-time domain).> There is hope that things could get better than what you see on your > scope. Especially, if your topology is the first one shown above. I > suspect you are making the noise measurement with a scope bandwidth > wider than your filter bandwidth. Correct? If true, that adds to the > fuzz on the trace because of the increased bandwidth. Also, are you > making the measurement with the sensor connected? > > Let your digital filter set your acquisition bandwidth. If you aren’t > already, use the second topology above. Terminate the input to your > amp/filter with the appropriate impedance and make the measurement with > your A/D and digital filter to determine your true system noise floor. > If it goes up when you add your sensor, well you know. > > It should be with a few dB of your calculation or you’ve got other > problems. You could also sweep your system using a sine source at the > input to verify measurement bandwidth. Just suck the data into MatLab > if you don’t have a canned FFT. Painful, but it works. > > All of the above applies to thermal noise and not the 1/f stuff.It still _can_ apply to the 1/f stuff, except that you can't use noise figures -- you have to use noise spectra at every step.> As Tim said, the digital filter will not fix any aliased stuff … you > have to stop that before it gets to the converter. Your analog filter > should do that. However, beware, depending on the self-resonance of > your filter components, you could very well have re-entrant modes at > Nyquest. So use your scope and a signal generator to sweep the A/D > pre-filter. > > Hope this helps.This last statement reminds me -- another thing that oversampling does for you is to ease your analog filter requirements -- when you sample way faster than the signal demands, it means that your analog filter can become simpler. Sometimes when you're using extreme oversampling (such as you get when you use some sigma-delta converters) your analog filter can just be a resistor and a cap, and still be sufficient. When you can reduce your analog filter to that extent (and if you have the processing power you need), life becomes much simpler. -- www.wescottdesign.com
Reply by ●September 30, 20112011-09-30
On Sep 30, 9:59�am, Tim Wescott <t...@seemywebsite.com> wrote:> On Thu, 29 Sep 2011 11:11:19 -0700, me0223 wrote: > > On Sep 29, 10:41�am, Tim Wescott <t...@seemywebsite.com> wrote: > >> On Thu, 29 Sep 2011 11:29:38 -0500, glias wrote: > >> >>On Sep 29, 8:03=A0am, Jerry Avins <j...@ieee.org> wrote: > >> >>> On 9/29/2011 9:31 AM, me0...@yahoo.com wrote: > > ** snip ** > > > > > > >> > So using the digital filter just permit to reduce the analog filter > >> > (anti aliasing) ? > > >> Using a filter in digital-land offers a multitude of advantages, about > >> the only thing it _doesn't_ do is undo the effects of aliasing -- that > >> would be like a blender that can un-scramble eggs. > > >> --www.wescottdesign.com-Hide quoted text - > > >> - Show quoted text - > > > Which topology are you using: > > Sensor--->Filter--->op-amp--->A/D > > or > > Sensor---> Op-Amp--->Filter--->A/D > > > For any amp string the noise performance of the system, i.e., the noise > > floor will be set by the first amp. �It can never be better than that. > > Another way to say it is, if you create noise in your amp string, you > > can�t see a signal from your input source better than that. > > > Any lossy components, (i.e. resistors, non-ideal filters), in front of > > an amplifier adds to the noise. > > You will never be able to see below the noise floor set by your system > > NF. > > > What process gain and averaging allow you to do, is get down to the > > noise floor of your gain chain. �So you want your narrowest filter to be > > the digital filter. �Noise Out of your gain stage = KTBGF. Consider your > > A/D as just another gain stage with a NF. > > The only quirk with thinking of the A/D as just another gain stage with a > NF is that the NF changes with sampling rate -- the noise power never > changes, but sampling faster spreads that noise power out (or scrunches > up the spectrum of the desired signal, depending on whether you're > looking at things from inside or outside the sampled-time domain). > > > > > > > There is hope that things could get better than what you see on your > > scope. �Especially, if your topology is the first one shown above. I > > suspect you are making the noise measurement with a scope bandwidth > > wider than your filter bandwidth. �Correct? �If true, that adds to the > > fuzz on the trace because of the increased bandwidth. �Also, are you > > making the measurement with the sensor connected? > > > Let your digital filter set your acquisition bandwidth. �If you aren�t > > already, use the second topology above. Terminate the input to your > > amp/filter with the appropriate impedance and make the measurement with > > your A/D and digital filter to determine your true system noise floor. > > If it goes up when you add your sensor, well you know. > > > It should be with a few dB of your calculation or you�ve got other > > problems. �You could also sweep your system using a sine source at the > > input to verify measurement bandwidth. �Just suck the data into MatLab > > if you don�t have a canned FFT. �Painful, but it works. > > > All of the above applies to thermal noise and not the 1/f stuff. > > It still _can_ apply to the 1/f stuff, except that you can't use noise > figures -- you have to use noise spectra at every step. > > > As Tim said, the digital filter will not fix any aliased stuff � you > > have to stop that before it gets to the converter. �Your analog filter > > should do that. �However, beware, depending on the self-resonance of > > your filter components, you could very well have re-entrant modes at > > Nyquest. �So use your scope and a signal generator to sweep the A/D > > pre-filter. > > > Hope this helps. > > This last statement reminds me -- another thing that oversampling does > for you is to ease your analog filter requirements -- when you sample way > faster than the signal demands, it means that your analog filter can > become simpler. �Sometimes when you're using extreme oversampling (such > as you get when you use some sigma-delta converters) your analog filter > can just be a resistor and a cap, and still be sufficient. > > When you can reduce your analog filter to that extent (and if you have > the processing power you need), life becomes much simpler. > > --www.wescottdesign.com- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -Hi Tim, When doing gain line-ups the A/D has to be included. The typical process is to calculate an equivalent NF and IIP3. Yes, NF in this type of calculation will include process gain, but that�s exactly the info you want when doing a rigorous design. This is especially critical when doing broadband acquisition systems that have large dynamic range requirements. You don�t want to go to fab and find out later you really screwed up because you were negligent in analysis. In this case, it sounds to me that the OP is trying to figure out if he�s up against the stops or not. The only way I know how to get ahead of the game is to do a complete paper analysis. Which in this case, is only a few minutes provided you know how to approach it. I think that�s what the OP was asking for, hopefully we didn�t lead him astray. As I�m sure you know, the other critical part of design is verification of assumptions. Sometimes folks just starting out don�t really have a good handle on how to do that. My goal was just to stimulate some though on how he might approach this. Re 1/f and NF � yup, these are totally different noise sources. Regards
Reply by ●September 30, 20112011-09-30
On Fri, 30 Sep 2011 10:56:35 -0700, me0223 wrote:> On Sep 30, 9:59 am, Tim Wescott <t...@seemywebsite.com> wrote: >> On Thu, 29 Sep 2011 11:11:19 -0700, me0223 wrote: >> > On Sep 29, 10:41 am, Tim Wescott <t...@seemywebsite.com> wrote: >> >> On Thu, 29 Sep 2011 11:29:38 -0500, glias wrote: >> >> >>On Sep 29, 8:03=A0am, Jerry Avins <j...@ieee.org> wrote: >> >> >>> On 9/29/2011 9:31 AM, me0...@yahoo.com wrote: >> >> ** snip ** >> >> >> >> >> >> >> > So using the digital filter just permit to reduce the analog >> >> > filter (anti aliasing) ? >> >> >> Using a filter in digital-land offers a multitude of advantages, >> >> about the only thing it _doesn't_ do is undo the effects of aliasing >> >> -- that would be like a blender that can un-scramble eggs. >> >> >> --www.wescottdesign.com-Hide quoted text - >> >> >> - Show quoted text - >> >> > Which topology are you using: >> > Sensor--->Filter--->op-amp--->A/D >> > or >> > Sensor---> Op-Amp--->Filter--->A/D >> >> > For any amp string the noise performance of the system, i.e., the >> > noise floor will be set by the first amp. It can never be better >> > than that. Another way to say it is, if you create noise in your amp >> > string, you can’t see a signal from your input source better than >> > that. >> >> > Any lossy components, (i.e. resistors, non-ideal filters), in front >> > of an amplifier adds to the noise. >> > You will never be able to see below the noise floor set by your >> > system NF. >> >> > What process gain and averaging allow you to do, is get down to the >> > noise floor of your gain chain. So you want your narrowest filter to >> > be the digital filter. Noise Out of your gain stage = KTBGF. >> > Consider your A/D as just another gain stage with a NF. >> >> The only quirk with thinking of the A/D as just another gain stage with >> a NF is that the NF changes with sampling rate -- the noise power never >> changes, but sampling faster spreads that noise power out (or scrunches >> up the spectrum of the desired signal, depending on whether you're >> looking at things from inside or outside the sampled-time domain). >> >> >> >> >> >> > There is hope that things could get better than what you see on your >> > scope. Especially, if your topology is the first one shown above. I >> > suspect you are making the noise measurement with a scope bandwidth >> > wider than your filter bandwidth. Correct? If true, that adds to >> > the fuzz on the trace because of the increased bandwidth. Also, are >> > you making the measurement with the sensor connected? >> >> > Let your digital filter set your acquisition bandwidth. If you >> > aren’t already, use the second topology above. Terminate the input to >> > your amp/filter with the appropriate impedance and make the >> > measurement with your A/D and digital filter to determine your true >> > system noise floor. If it goes up when you add your sensor, well you >> > know. >> >> > It should be with a few dB of your calculation or you’ve got other >> > problems. You could also sweep your system using a sine source at >> > the input to verify measurement bandwidth. Just suck the data into >> > MatLab if you don’t have a canned FFT. Painful, but it works. >> >> > All of the above applies to thermal noise and not the 1/f stuff. >> >> It still _can_ apply to the 1/f stuff, except that you can't use noise >> figures -- you have to use noise spectra at every step. >> >> > As Tim said, the digital filter will not fix any aliased stuff … you >> > have to stop that before it gets to the converter. Your analog >> > filter should do that. However, beware, depending on the >> > self-resonance of your filter components, you could very well have >> > re-entrant modes at Nyquest. So use your scope and a signal >> > generator to sweep the A/D pre-filter. >> >> > Hope this helps. >> >> This last statement reminds me -- another thing that oversampling does >> for you is to ease your analog filter requirements -- when you sample >> way faster than the signal demands, it means that your analog filter >> can become simpler. Sometimes when you're using extreme oversampling >> (such as you get when you use some sigma-delta converters) your analog >> filter can just be a resistor and a cap, and still be sufficient. >> >> When you can reduce your analog filter to that extent (and if you have >> the processing power you need), life becomes much simpler. >> >> --www.wescottdesign.com- Hide quoted text - >> >> - Show quoted text -- Hide quoted text - >> >> - Show quoted text - > > > > Hi Tim, > > When doing gain line-ups the A/D has to be included. The typical > process is to calculate an equivalent NF and IIP3.That's the typical process if you're designing a radio, but at baseband I usually see things just done with power spectral densities. Also, at baseband, IIP3 is rarely the most important measure of distortion.> Yes, NF in this type > of calculation will include process gain, but that’s exactly the info > you want when doing a rigorous design. This is especially critical when > doing broadband acquisition systems that have large dynamic range > requirements. You don’t want to go to fab and find out later you really > screwed up because you were negligent in analysis. > > In this case, it sounds to me that the OP is trying to figure out if > he’s up against the stops or not. The only way I know how to get ahead > of the game is to do a complete paper analysis. Which in this case, is > only a few minutes provided you know how to approach it. I think > that’s what the OP was asking for, hopefully we didn’t lead him astray. > > As I’m sure you know, the other critical part of design is verification > of assumptions. Sometimes folks just starting out don’t really have a > good handle on how to do that. My goal was just to stimulate some > though on how he might approach this.It's often difficult -- particularly when you're trying to design by some cookbook -- to even know what the underlying assumptions _are_. So yes, the OP needs to think deeper, if he's got enough background to do so.> Re 1/f and NF … yup, these are totally different noise sources. > > Regards-- www.wescottdesign.com
Reply by ●September 30, 20112011-09-30
On Sep 30, 1:17�pm, Tim Wescott <t...@seemywebsite.com> wrote:> On Fri, 30 Sep 2011 10:56:35 -0700, me0223 wrote: > > On Sep 30, 9:59�am, Tim Wescott <t...@seemywebsite.com> wrote: > >> On Thu, 29 Sep 2011 11:11:19 -0700, me0223 wrote: > >> > On Sep 29, 10:41�am, Tim Wescott <t...@seemywebsite.com> wrote: > >> >> On Thu, 29 Sep 2011 11:29:38 -0500, glias wrote: > >> >> >>On Sep 29, 8:03=A0am, Jerry Avins <j...@ieee.org> wrote: > >> >> >>> On 9/29/2011 9:31 AM, me0...@yahoo.com wrote: > > >> ** snip ** > > >> >> > So using the digital filter just permit to reduce the analog > >> >> > filter (anti aliasing) ? > > >> >> Using a filter in digital-land offers a multitude of advantages, > >> >> about the only thing it _doesn't_ do is undo the effects of aliasing > >> >> -- that would be like a blender that can un-scramble eggs. > > >> >> --www.wescottdesign.com-Hidequoted text - > > >> >> - Show quoted text - > > >> > Which topology are you using: > >> > Sensor--->Filter--->op-amp--->A/D > >> > or > >> > Sensor---> Op-Amp--->Filter--->A/D > > >> > For any amp string the noise performance of the system, i.e., the > >> > noise floor will be set by the first amp. �It can never be better > >> > than that. Another way to say it is, if you create noise in your amp > >> > string, you can�t see a signal from your input source better than > >> > that. > > >> > Any lossy components, (i.e. resistors, non-ideal filters), in front > >> > of an amplifier adds to the noise. > >> > You will never be able to see below the noise floor set by your > >> > system NF. > > >> > What process gain and averaging allow you to do, is get down to the > >> > noise floor of your gain chain. �So you want your narrowest filter to > >> > be the digital filter. �Noise Out of your gain stage = KTBGF. > >> > Consider your A/D as just another gain stage with a NF. > > >> The only quirk with thinking of the A/D as just another gain stage with > >> a NF is that the NF changes with sampling rate -- the noise power never > >> changes, but sampling faster spreads that noise power out (or scrunches > >> up the spectrum of the desired signal, depending on whether you're > >> looking at things from inside or outside the sampled-time domain). > > >> > There is hope that things could get better than what you see on your > >> > scope. �Especially, if your topology is the first one shown above. I > >> > suspect you are making the noise measurement with a scope bandwidth > >> > wider than your filter bandwidth. �Correct? �If true, that adds to > >> > the fuzz on the trace because of the increased bandwidth. �Also, are > >> > you making the measurement with the sensor connected? > > >> > Let your digital filter set your acquisition bandwidth. �If you > >> > aren�t already, use the second topology above. Terminate the input to > >> > your amp/filter with the appropriate impedance and make the > >> > measurement with your A/D and digital filter to determine your true > >> > system noise floor. If it goes up when you add your sensor, well you > >> > know. > > >> > It should be with a few dB of your calculation or you�ve got other > >> > problems. �You could also sweep your system using a sine source at > >> > the input to verify measurement bandwidth. �Just suck the data into > >> > MatLab if you don�t have a canned FFT. �Painful, but it works. > > >> > All of the above applies to thermal noise and not the 1/f stuff. > > >> It still _can_ apply to the 1/f stuff, except that you can't use noise > >> figures -- you have to use noise spectra at every step. > > >> > As Tim said, the digital filter will not fix any aliased stuff � you > >> > have to stop that before it gets to the converter. �Your analog > >> > filter should do that. �However, beware, depending on the > >> > self-resonance of your filter components, you could very well have > >> > re-entrant modes at Nyquest. �So use your scope and a signal > >> > generator to sweep the A/D pre-filter. > > >> > Hope this helps. > > >> This last statement reminds me -- another thing that oversampling does > >> for you is to ease your analog filter requirements -- when you sample > >> way faster than the signal demands, it means that your analog filter > >> can become simpler. �Sometimes when you're using extreme oversampling > >> (such as you get when you use some sigma-delta converters) your analog > >> filter can just be a resistor and a cap, and still be sufficient. > > >> When you can reduce your analog filter to that extent (and if you have > >> the processing power you need), life becomes much simpler. > > >> --www.wescottdesign.com-Hide quoted text - > > >> - Show quoted text -- Hide quoted text - > > >> - Show quoted text - > > > Hi Tim, > > > When doing gain line-ups the A/D has to be included. �The typical > > process is to calculate an equivalent NF and IIP3. > > That's the typical process if you're designing a radio, but at baseband I > usually see things just done with power spectral densities. �Also, at > baseband, IIP3 is rarely the most important measure of distortion. > > > > > > > Yes, NF in this type > > of calculation will include process gain, but that�s exactly the info > > you want when doing a rigorous design. �This is especially critical when > > doing broadband acquisition systems that have large dynamic range > > requirements. �You don�t want to go to fab and find out later you really > > screwed up because you were negligent in analysis. > > > In this case, it sounds to me that the OP is trying to figure out if > > he�s up against the stops or not. �The only way I know how to get ahead > > of the game is to do a complete paper analysis. �Which in this case, is > > only a few minutes provided you know how to approach it. � I think > > that�s what the OP was asking for, hopefully we didn�t lead him astray. > > > As I�m sure you know, the other critical part of design is verification > > of assumptions. Sometimes folks just starting out don�t really have a > > good handle on how to do that. �My goal was just to stimulate some > > though on how he might approach this. > > It's often difficult -- particularly when you're trying to design by some > cookbook -- to even know what the underlying assumptions _are_. �So yes, > the OP needs to think deeper, if he's got enough background to do so. > > > Re 1/f and NF � yup, these are totally different noise sources. > > > Regards > > --www.wescottdesign.com- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -Yeah, when you think about it, practically everything dumps down to baseband now days, even radios. But your point is well taken; NF and IIP3 are unfamiliar terms to many analog guys. In the old days analog was divided between the time domain and the frequency domain guys. The time domain guys were more into step response and % distortion, and frequency domain guys into the IIP3. Maybe frequency range had a lot more to do with it, audio/ video vs rf. I still recall spec�ing stuff for % distortion as a function of a 1vp-p square wave at the top of acquisition window. The only reason, (that I can think of), that psd is still used when dealing with op-amps is because the final No is network dependent. But as a user, what you want is the total noise contribution of that stage as a function of frequency, not a plot of the op-amp�s psd curve. NF and IIP3 are just convenient terms to work with. Both from a design and verification stand point. Especially in band limited acquisitions. Does IIP3 do a complete job of predicting all nonlinear effects, no! But it�s a fairly good first order indicator. If you can relate your measurements to two tones you got a shot. Some time back Analog Devices started spec�ing their A/D drivers with an equivalent IIP3. Spec�ing of high performance A/D�s these days is done using two tone measurements as opposed to the old sine curve effective bits stuff. But you�re right the concept is all the same, you can convert this stuff to fit your needs, you just need to know what you�re after. Regards
Reply by ●September 30, 20112011-09-30
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. > RegardsTake a sample from the A/D and compute an FFT with the input shorted, this will indicate the noise of your front system from the detector noise, to some degree at least. You can't do anything about noise generated by your detector in the frequency range of your input, that is a sensor limitation that bounds the best you can do. Signal to noise ratios implies a bandwidth of fs/2, if you reduce the bandwidth of interest you reduce the noise by the same amount.
Reply by ●October 3, 20112011-10-03
>On Sep 29, 10:41=A0am, Tim Wescott <t...@seemywebsite.com> wrote: >> On Thu, 29 Sep 2011 11:29:38 -0500, glias wrote: >> >>On Sep 29, 8:03=3DA0am, 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> >> > =3DA0wrote: >> >>> >> Hello all, >> >>> >> I have IR preamp with a gain of 64dB, the output noise is about >> >>> >> 50mV >> > p=3D >> >>eak >> >>> >> to peak for a signal of 4V peak peak (max) and the bandwidth is >> > 350kHz=3D >> >>. >> >>> >> I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisientfo=>r >> > 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=3D >> >>n my >> >>> >> band of interest ...? is it possible ? Does the oversamplingcould>> > hel=3D >> >>p me >> >>> >> to reduce it ? or does it only improves the quantification noiseo=>f >> > th=3D >> >>e ADC >> >>> >> ? >> >>> >> Does it exist another (digital) way to help me to reduce thenoise>> >>> >> ? >> > D=3D >> >>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 rangetha=>t >> >>> > can be used to calculate the noise floor. >> >> >>> > No =3D3D (KTBGF) >> >> >>> > F =3D3D ((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 Bwai=>s >> >>> > the final analysis bandwidth. >> >> >>> > So calculate the NF of the amp, NF of the A/D and everythingfalls>> >>> > out. >> >> >>> > Regards, >> >>> > Hope this helps >> >> >>> Hardly! He asked how to filter. (Not that the question has ananswer>> >>> with the information given.) >> >> >>> Jerry >> >>> -- >> >>> Engineering is the art of making what you want from things you can >> >>> get.- >> > =3D >> >>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 howhe>> >>might use the concept of noise to solve his problem. >> >> >>It looks to me like he=3D92s taking a measurement and reading the fuzz=>on >> >>a scope trace. =A0But I don=3D92t know. >> >> >>An interested student would ask where those equations come from andhow>> >>he could use them to solve his problem. >> >> >>The concept of how to design a gain lineup, whether that be a op-ampan=>d >> >>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 =3D85 but he doesh=>ave >> >>access to the solution. =A0He 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 anda>> > real problem (for me). >> > The bandwidth of the analog front end (bias and pre amp of thedetector>> > is have a high pass filter (a simple first order ac coupling) with1,5H=>z >> > 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 >> >> So the bandwidth of your _filter_ is 350kHz, fin. =A0But what is theusef=>ul >> bandwidth of your _signal_? >> >> > 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 techniquepermit>> > to reduce the noise from the quantification noise from the ADC.(correc=>t >> > me if I'm wrong !). >> >> More or less correct, yes. =A0_If_ the ADC has enough intrinsic noisetha=>t >> it shows up in the ADC output, then yes, oversampling and averaging can >> help you to overcome quantization noise. >> >> > But it doesn't reduce the noise which come from my >> > analog signal chain, isn't it ? >> >> Correct. =A0It can't do a thing about that. >> >> > I guess that the only solution to my problem is to improve the analog >> > chain . ? >> >> Unless your analog low-pass filter is wider than necessary, or yournoise>> is being introduced after it, yes. >> >> > So using the digital filter just permit to reduce the analog filter >> > (anti aliasing) ? >> >> Using a filter in digital-land offers a multitude of advantages, about >> the only thing it _doesn't_ do is undo the effects of aliasing -- that >> would be like a blender that can un-scramble eggs. >> >> --www.wescottdesign.com- Hide quoted text - >> >> - Show quoted text - > > >Which topology are you using: >Sensor--->Filter--->op-amp--->A/D >or >Sensor---> Op-Amp--->Filter--->A/D > >For any amp string the noise performance of the system, i.e., the >noise floor will be set by the first amp. It can never be better than >that. Another way to say it is, if you create noise in your amp >string, you can=92t see a signal from your input source better than >that. > >Any lossy components, (i.e. resistors, non-ideal filters), in front of >an amplifier adds to the noise. >You will never be able to see below the noise floor set by your system >NF. > >What process gain and averaging allow you to do, is get down to the >noise floor of your gain chain. So you want your narrowest filter to >be the digital filter. Noise Out of your gain stage =3D KTBGF. >Consider your A/D as just another gain stage with a NF. > >There is hope that things could get better than what you see on your >scope. Especially, if your topology is the first one shown above. >I suspect you are making the noise measurement with a scope bandwidth >wider than your filter bandwidth. Correct? If true, that adds to the >fuzz on the trace because of the increased bandwidth. Also, are you >making the measurement with the sensor connected? > >Let your digital filter set your acquisition bandwidth. If you aren=92t >already, use the second topology above. >Terminate the input to your amp/filter with the appropriate impedance >and make the measurement with your A/D and digital filter to determine >your true system noise floor. If it goes up when you add your sensor, >well you know. > >It should be with a few dB of your calculation or you=92ve got other >problems. You could also sweep your system using a sine source at the >input to verify measurement bandwidth. Just suck the data into MatLab >if you don=92t have a canned FFT. Painful, but it works. > >All of the above applies to thermal noise and not the 1/f stuff. > >As Tim said, the digital filter will not fix any aliased stuff =85 you >have to stop that before it gets to the converter. Your analog filter >should do that. However, beware, depending on the self-resonance of >your filter components, you could very well have re-entrant modes at >Nyquest. So use your scope and a signal generator to sweep the A/D >pre-filter. > >Hope this helps. >Hello, thanks a lot for your help and sorry for my late answer. The bandwidth of the signal is 50Hz to 314kHz. For the topology, I have : Sensor---> Op-Amp--->Filter--->A/D I though that the "oversampling" method permit to reduce white noise provided by op amp, detector resistor and ADC quantification noise... but if I understand well, It only permits to reduce quantification noise. I would want to know how can I calculate the noise factor of my analog chain. Since the noise factor more used in RF components, there is no value of it in datasheet in low noise op amp like the ADA4898 (this is this op amp that I use for all my stages : pre-amp and filter stages since that I have low impedance sensor => I have to use a low noise voltage op amp). Could you please help me how I can do to calculate the NF with this op amp ? regards
Reply by ●October 3, 20112011-10-03
On Mon, 03 Oct 2011 07:28:32 -0500, glias wrote:>>On Sep 29, 10:41=A0am, Tim Wescott <t...@seemywebsite.com> wrote: >>> On Thu, 29 Sep 2011 11:29:38 -0500, glias wrote: >>> >>On Sep 29, 8:03=3DA0am, 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> >>> > =3DA0wrote: >>> >>> >> Hello all, >>> >>> >> I have IR preamp with a gain of 64dB, the output noise is about >>> >>> >> 50mV >>> > p=3D >>> >>eak >>> >>> >> to peak for a signal of 4V peak peak (max) and the bandwidth is >>> > 350kHz=3D >>> >>. >>> >>> >> I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisient > fo= >>r >>> > 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=3D >>> >>n my >>> >>> >> band of interest ...? is it possible ? Does the oversampling > could >>> > hel=3D >>> >>p me >>> >>> >> to reduce it ? or does it only improves the quantification >>> >>> >> noise > o= >>f >>> > th=3D >>> >>e ADC >>> >>> >> ? >>> >>> >> Does it exist another (digital) way to help me to reduce the > noise >>> >>> >> ? >>> > D=3D >>> >>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 > tha= >>t >>> >>> > can be used to calculate the noise floor. >>> >>> >>> > No =3D3D (KTBGF) >>> >>> >>> > F =3D3D ((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 > i= >>s >>> >>> > 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.- >>> > =3D >>> >>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=3D92s taking a measurement and reading the >>> >>fuzz > = >>on >>> >>a scope trace. =A0But I don=3D92t 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 > an= >>d >>> >>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 =3D85 but he >>> >>does > h= >>ave >>> >>access to the solution. =A0He 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 > 1,5H= >>z >>> > 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 >>> >>> So the bandwidth of your _filter_ is 350kHz, fin. =A0But what is the > usef= >>ul >>> bandwidth of your _signal_? >>> >>> > 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. > (correc= >>t >>> > me if I'm wrong !). >>> >>> More or less correct, yes. =A0_If_ the ADC has enough intrinsic noise > tha= >>t >>> it shows up in the ADC output, then yes, oversampling and averaging >>> can help you to overcome quantization noise. >>> >>> > But it doesn't reduce the noise which come from my analog signal >>> > chain, isn't it ? >>> >>> Correct. =A0It can't do a thing about that. >>> >>> > I guess that the only solution to my problem is to improve the >>> > analog chain . ? >>> >>> Unless your analog low-pass filter is wider than necessary, or your > noise >>> is being introduced after it, yes. >>> >>> > So using the digital filter just permit to reduce the analog filter >>> > (anti aliasing) ? >>> >>> Using a filter in digital-land offers a multitude of advantages, about >>> the only thing it _doesn't_ do is undo the effects of aliasing -- that >>> would be like a blender that can un-scramble eggs. >>> >>> --www.wescottdesign.com- Hide quoted text - >>> >>> - Show quoted text - >> >> >>Which topology are you using: >>Sensor--->Filter--->op-amp--->A/D >>or >>Sensor---> Op-Amp--->Filter--->A/D >> >>For any amp string the noise performance of the system, i.e., the noise >>floor will be set by the first amp. It can never be better than that. >>Another way to say it is, if you create noise in your amp string, you >>can=92t see a signal from your input source better than that. >> >>Any lossy components, (i.e. resistors, non-ideal filters), in front of >>an amplifier adds to the noise. >>You will never be able to see below the noise floor set by your system >>NF. >> >>What process gain and averaging allow you to do, is get down to the >>noise floor of your gain chain. So you want your narrowest filter to be >>the digital filter. Noise Out of your gain stage =3D KTBGF. Consider >>your A/D as just another gain stage with a NF. >> >>There is hope that things could get better than what you see on your >>scope. Especially, if your topology is the first one shown above. I >>suspect you are making the noise measurement with a scope bandwidth >>wider than your filter bandwidth. Correct? If true, that adds to the >>fuzz on the trace because of the increased bandwidth. Also, are you >>making the measurement with the sensor connected? >> >>Let your digital filter set your acquisition bandwidth. If you aren=92t >>already, use the second topology above. Terminate the input to your >>amp/filter with the appropriate impedance and make the measurement with >>your A/D and digital filter to determine your true system noise floor. >>If it goes up when you add your sensor, well you know. >> >>It should be with a few dB of your calculation or you=92ve got other >>problems. You could also sweep your system using a sine source at the >>input to verify measurement bandwidth. Just suck the data into MatLab >>if you don=92t have a canned FFT. Painful, but it works. >> >>All of the above applies to thermal noise and not the 1/f stuff. >> >>As Tim said, the digital filter will not fix any aliased stuff =85 you >>have to stop that before it gets to the converter. Your analog filter >>should do that. However, beware, depending on the self-resonance of >>your filter components, you could very well have re-entrant modes at >>Nyquest. So use your scope and a signal generator to sweep the A/D >>pre-filter. >> >>Hope this helps. >> >> > > Hello, > thanks a lot for your help and sorry for my late answer. > > The bandwidth of the signal is 50Hz to 314kHz. For the topology, I have > : > Sensor---> Op-Amp--->Filter--->A/D > > I though that the "oversampling" method permit to reduce white noise > provided by op amp, detector resistor and ADC quantification noise... > but if I understand well, It only permits to reduce quantification > noise. I would want to know how can I calculate the noise factor of my > analog chain. Since the noise factor more used in RF components, there > is no value of it in datasheet in low noise op amp like the ADA4898 > (this is this op amp that I use for all my stages : pre-amp and filter > stages since that I have low impedance sensor => I have to use a low > noise voltage op amp). Could you please help me how I can do to > calculate the NF with this op amp ?The oversampling and averaging technique does, indeed work to reduce the effect of any white noise before the ADC conversion (actually, any bandlimited noise that's above the Nyquist rate of the sampling -- true white noise would be of infinite power at the ADC, and would screw up your measurement infinitely). This applies to noise both inside and outside of the ADC. You can work this out on paper: for noise that's of significantly higher bandwidth than your sampling rate, the "after- sampling" noise magnitude is always the same. Because faster sampling spreads out the after-sampling spectrum, the noise power spectral density for that component of noise gets spread out. You _should_ be able to bandlimit the op-amp noise, and leave yourself with just the noise on the output of your filter (of which there will be some, if it's an active filter) and the (generally) quite considerable noise at the input of the ADC. The oversample-and-average technique actually doesn't reduce quantization noise by itself: if you had an infinitely quiet ADC front end then the quantization noise would come through unscathed. What reduces the quantization noise is the contribution of the high-bandwidth noise that 'scrambles' the quantization noise, making it whiter. Then the out-of- band components of the quantization noise can be filtered out. If you had an ADC that was too quiet you could fix it up by dithering the input or otherwise adding noise. Sigma-delta converters, in fact, are set up to inherently generate this "dithering" in such a way that the noise PSD is shaped away from the desired signal PSD, allowing the filtering to work much better than it would with random noise. Really, working this out on paper would help to make sense of it all. -- www.wescottdesign.com
Reply by ●October 3, 20112011-10-03
On Oct 3, 5:28=A0am, "glias" <glias37@n_o_s_p_a_m.hotmail.com> wrote:> >On Sep 29, 10:41=3DA0am, Tim Wescott <t...@seemywebsite.com> wrote: > >> On Thu, 29 Sep 2011 11:29:38 -0500, glias wrote: > >> >>On Sep 29, 8:03=3D3DA0am, 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> > >> > =3D3DA0wrote: > >> >>> >> Hello all, > >> >>> >> I have IR preamp with a gain of 64dB, the output noise is about > >> >>> >> 50mV > >> > p=3D3D > >> >>eak > >> >>> >> to peak for a signal of 4V peak peak (max) and the bandwidth is > >> > 350kHz=3D3D > >> >>. > >> >>> >> I have a AD7626 (16 bits 10MSPS ADC) which is largly suffisient > fo=3D > >r > >> > my > >> >>> >> aplpication. > >> >>> >> I would want to know what would be the best method to filter th=e> >> > noise > >> >>> >> (which is white noise and 1/f noise which come from the IR > >> >>> >> detector) > >> > i=3D3D > >> >>n my > >> >>> >> band of interest ...? is it possible ? Does the oversampling > could > >> > hel=3D3D > >> >>p me > >> >>> >> to reduce it ? or does it only improves the quantification nois=e> o=3D > >f > >> > th=3D3D > >> >>e ADC > >> >>> >> ? > >> >>> >> Does it exist another (digital) way to help me to reduce the > noise > >> >>> >> ? > >> > D=3D3D > >> >>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 th=e> >> >>> > system. > > >> >>> > Once you get that number you can solve for system dynamic range > tha=3D > >t > >> >>> > can be used to calculate the noise floor. > > >> >>> > No =3D3D3D (KTBGF) > > >> >>> > F =3D3D3D ((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 Bw=a> i=3D > >s > >> >>> > 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.- > >> > =3D3D > >> >>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=3D3D92s taking a measurement and reading the =fuzz> =3D > >on > >> >>a scope trace. =3DA0But I don=3D3D92t 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 > an=3D > >d > >> >>A/D or a downconvert with a A/D behind and solve for noise is all th=e> >> >>same. > > >> >>Simple concepts such as where to place that narrowband filter and wh=y> >> >>elude many. > > >> >>Never did I say that he supplied enough information =3D3D85 but he d=oes> h=3D > >ave > >> >>access to the solution. =3DA0He 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 an=d> 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 > 1,5H=3D > >z > >> > 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 spectru=m> >> > analyzer so > > >> So the bandwidth of your _filter_ is 350kHz, fin. =3DA0But what is the > usef=3D > >ul > >> bandwidth of your _signal_? > > >> > 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. > (correc=3D > >t > >> > me if I'm wrong !). > > >> More or less correct, yes. =3DA0_If_ the ADC has enough intrinsic nois=e> tha=3D > >t > >> it shows up in the ADC output, then yes, oversampling and averaging ca=n> >> help you to overcome quantization noise. > > >> > But it doesn't reduce the noise which come from my > >> > analog signal chain, isn't it ? > > >> Correct. =3DA0It can't do a thing about that. > > >> > I guess that the only solution to my problem is to improve the analo=g> >> > chain . ? > > >> Unless your analog low-pass filter is wider than necessary, or your > noise > >> is being introduced after it, yes. > > >> > So using the digital filter just permit to reduce the analog filter > >> > (anti aliasing) ? > > >> Using a filter in digital-land offers a multitude of advantages, about > >> the only thing it _doesn't_ do is undo the effects of aliasing -- that > >> would be like a blender that can un-scramble eggs. > > >> --www.wescottdesign.com-Hide quoted text - > > >> - Show quoted text - > > >Which topology are you using: > >Sensor--->Filter--->op-amp--->A/D > >or > >Sensor---> Op-Amp--->Filter--->A/D > > >For any amp string the noise performance of the system, i.e., the > >noise floor will be set by the first amp. =A0It can never be better than > >that. =A0Another way to say it is, if you create noise in your amp > >string, you can=3D92t see a signal from your input source better than > >that. > > >Any lossy components, (i.e. resistors, non-ideal filters), in front of > >an amplifier adds to the noise. > >You will never be able to see below the noise floor set by your system > >NF. > > >What process gain and averaging allow you to do, is get down to the > >noise floor of your gain chain. =A0So you want your narrowest filter to > >be the digital filter. =A0Noise Out of your gain stage =3D3D KTBGF. > >Consider your A/D as just another gain stage with a NF. > > >There is hope that things could get better than what you see on your > >scope. =A0Especially, if your topology is the first one shown above. > >I suspect you are making the noise measurement with a scope bandwidth > >wider than your filter bandwidth. =A0Correct? =A0If true, that adds to t=he> >fuzz on the trace because of the increased bandwidth. =A0Also, are you > >making the measurement with the sensor connected? > > >Let your digital filter set your acquisition bandwidth. =A0If you aren==3D92t> >already, use the second topology above. > >Terminate the input to your amp/filter with the appropriate impedance > >and make the measurement with your A/D and digital filter to determine > >your true system noise floor. =A0If it goes up when you add your sensor, > >well you know. > > >It should be with a few dB of your calculation or you=3D92ve got other > >problems. =A0You could also sweep your system using a sine source at the > >input to verify measurement bandwidth. =A0Just suck the data into MatLab > >if you don=3D92t have a canned FFT. =A0Painful, but it works. > > >All of the above applies to thermal noise and not the 1/f stuff. > > >As Tim said, the digital filter will not fix any aliased stuff =3D85 you > >have to stop that before it gets to the converter. =A0Your analog filter > >should do that. =A0However, beware, depending on the self-resonance of > >your filter components, you could very well have re-entrant modes at > >Nyquest. =A0So use your scope and a signal generator to sweep the A/D > >pre-filter. > > >Hope this helps. > > Hello, > thanks a lot for your help and sorry for my late answer. > > The bandwidth of the signal is 50Hz to 314kHz. > For the topology, I have : > Sensor---> Op-Amp--->Filter--->A/D > > I though that the "oversampling" method permit to reduce white noise > provided by op amp, detector resistor and ADC quantification noise... but > if I understand well, It only permits to reduce quantification noise. > I would want to know how can I calculate the noise factor of my analog > chain. Since the noise factor more used in RF components, there is no val=ue> of it in datasheet in low noise op amp like the ADA4898 (this is this op > amp that I use for all my stages : pre-amp and filter stages since that I > have low impedance sensor =3D> I have to use a low noise voltage op amp). > Could you please help me how I can do to calculate the NF with this op am=p> ? > > regards- Hide quoted text - > > - Show quoted text -The OP-Amp guys spec noise in terms of input referred voltage and current of their op-amp, the active device In order to calculate NF you need those numbers, your circuit topology and the values of those components. The analysis goes like this: Use the input referred voltage and current noise along with the total input referred noise from your circuit topology to calculate the input spectral density. Apply the noise to the definition of noise factor, F, and solve for NF which is the decibel equivalent. You can now use that NF number in calculating your system noise, noise floor and hence your dynamic range as function of frequency. These concepts maybe seem strange, but once you get it, they are very useful. Build yourself a lib of circuit topologies and just plug in component values. Years ago TI put out some papers on this subject. They did a pretty good job. Search their site. Also a couple of old text books, that maybe helpful, I don=92t know if they=92re still in print: One by a guy named Mervin Frerking, (I think I spelled his name correctly), called Digitial Signal Processing in Radio Comm System, or something like that. Covers RF gain line up including the A/D. His terminology may seem strange but the concepts are there. Also a pure RF book, Introduction to Radio Frequency Design by Wes Hayward. Great book for getting the basics down re elements in a gain stage that effect dynamic range. No A/D stuff. And of course I suspect there are several newer books that cover this stuff, others may be of some help. Regards
Reply by ●October 3, 20112011-10-03
On Oct 3, 1:06=A0pm, Tim Wescott <t...@seemywebsite.com> wrote:> The oversample-and-average technique actually doesn't reduce quantization > noise by itself: if you had an infinitely quiet ADC front end then the > quantization noise would come through unscathed. =A0that's only true for DC inputs, which the OP states is not under consideration quantization noise is most often modeled as just broad band noise extending way past fs/2, with no oversampling most of the noise power is folded back into the analysis band (1.5k to 350k ), oversampling just increases the folding frequency, thus reducing the amount of high frequency aliased noise (from any source) folded back into the analysis band
