I need to measure the time it takes signal to turn on and be at steady state frequency (1 to 10MHz)to within 200hz resolution within 2us. The kicker is that I can only sample at 65MSPS. Is this possible? I can get 200hz resolution by sampling for 5ms, but I am only interested in the sample from 0 to 2us, so when I window that section, I loose my resolution. If this problem interests you, I can provide more information on request.
time to frequency measurement
Started by ●November 1, 2006
Reply by ●November 1, 20062006-11-01
alexs wrote:> I need to measure the time it takes signal to turn on and be at steady > state frequency (1 to 10MHz)to within 200hz resolution within 2us. The > kicker is that I can only sample at 65MSPS. Is this possible? I can > get 200hz resolution by sampling for 5ms, but I am only interested in > the sample from 0 to 2us, so when I window that section, I loose my > resolution. If this problem interests you, I can provide more > information on request. >The kicker isn't that you can only sample at 65 Msps, it's that you can only use 2 us of data. That constraint limits your resolution to 500 kHz, no matter what the sample rate is. I think some more info would be helpful. John
Reply by ●November 1, 20062006-11-01
John Sampson wrote:> alexs wrote: > >> I need to measure the time it takes signal to turn on and be at steady >> state frequency (1 to 10MHz)to within 200hz resolution within 2us. The >> kicker is that I can only sample at 65MSPS. Is this possible? I can >> get 200hz resolution by sampling for 5ms, but I am only interested in >> the sample from 0 to 2us, so when I window that section, I loose my >> resolution. If this problem interests you, I can provide more >> information on request. >> > > The kicker isn't that you can only sample at 65 Msps, it's that you can > only use 2 us of data. That constraint limits your resolution to 500 > kHz, no matter what the sample rate is.Very wrong statement. There is absolutely no relation between the duration of the data and the frequency resolution. The only thing that matters is the SNR. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●November 1, 20062006-11-01
alexs wrote:> I need to measure the time it takes signal to turn on and be at steady > state frequency (1 to 10MHz)to within 200hz resolution within 2us. The > kicker is that I can only sample at 65MSPS. Is this possible?It may or may not be possible. It depends. If you can describe your task in details, can give you a more focused answer. The contact email is on the website. I can> get 200hz resolution by sampling for 5ms, but I am only interested in > the sample from 0 to 2us, so when I window that section, I loose my > resolution. If this problem interests you, I can provide more > information on request. >Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●November 1, 20062006-11-01
Vladimir Vassilevsky wrote:> > > John Sampson wrote: > >> alexs wrote: >> >>> I need to measure the time it takes signal to turn on and be at steady >>> state frequency (1 to 10MHz)to within 200hz resolution within 2us. The >>> kicker is that I can only sample at 65MSPS. Is this possible? I can >>> get 200hz resolution by sampling for 5ms, but I am only interested in >>> the sample from 0 to 2us, so when I window that section, I loose my >>> resolution. If this problem interests you, I can provide more >>> information on request. >>> >> >> The kicker isn't that you can only sample at 65 Msps, it's that you >> can only use 2 us of data. That constraint limits your resolution to >> 500 kHz, no matter what the sample rate is. > > > Very wrong statement. > > There is absolutely no relation between the duration of the data and the > frequency resolution. The only thing that matters is the SNR. >And the nature of the signal. If it's a guaranteed sine wave, or just about anything else that has some guaranteed curvature at a given point in it's progress, then it's possible. If it's a square wave, or if it's a sine wave with some unknown level of harmonics, or a triangle wave with an unknown amplitude -- then you're out of luck. As with Vladimir, my email is on the website (mine, not his). You've got a long row to hoe with this one, but either of us can tell you if it's a doable proposition. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●November 1, 20062006-11-01
Vladimir Vassilevsky <antispam_bogus@hotmail.com> writes:> John Sampson wrote: > >> alexs wrote: >> >>> I need to measure the time it takes signal to turn on and be at steady >>> state frequency (1 to 10MHz)to within 200hz resolution within 2us. The >>> kicker is that I can only sample at 65MSPS. Is this possible? I can >>> get 200hz resolution by sampling for 5ms, but I am only interested in >>> the sample from 0 to 2us, so when I window that section, I loose my >>> resolution. If this problem interests you, I can provide more >>> information on request. >>> >> The kicker isn't that you can only sample at 65 Msps, it's that you >> can only use 2 us of data. That constraint limits your resolution to >> 500 kHz, no matter what the sample rate is. > > Very wrong statement. > > There is absolutely no relation between the duration of the data and > the frequency resolution. The only thing that matters is the SNR.I agree with Vladimir. Consider this gedanken. You have a pure sine wave that's been sampled and input to a Hilbert transformer since the beginning of time. You select two [complex] samples, 0*T and 1*T, from this infinite stream and compute f = (arctan2(x1.y/x1.x) - arctan2(x0.y/x0.x)) / T. This frequency is perfect with just two samples if there is no noise. -- % Randy Yates % "Though you ride on the wheels of tomorrow, %% Fuquay-Varina, NC % you still wander the fields of your %%% 919-577-9882 % sorrow." %%%% <yates@ieee.org> % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr
Reply by ●November 1, 20062006-11-01
alexs wrote:> I need to measure the time it takes signal to turn on and be at steady > state frequency (1 to 10MHz)to within 200hz resolution within 2us. The > kicker is that I can only sample at 65MSPS. Is this possible? I can > get 200hz resolution by sampling for 5ms, but I am only interested in > the sample from 0 to 2us, so when I window that section, I loose my > resolution.Why are you only interested in the sample from 0 to 2 uS? Does your signal random change by an abitrary amount every 2 uS? It seems like you could use the entire history. For instance the phase vocoder technique uses data from the previous fft sections. If the peak bin is the same, the noise level is low enough, and the phase has been changing by a small enough amount, you might be able to determine frequency trajectory and stability to a resolution much finer than 1/(2 uS). If your signal-to-noise ratio is low enough, then you might be able to compute the frequency, amplitude and phase from just 3 samples (3 equations in 3 unknowns). IMHO. YMMV. -- rhn A.T nicholson d.0.t C-o-M
Reply by ●November 1, 20062006-11-01
Vladimir Vassilevsky wrote:> John Sampson wrote: > > > alexs wrote: > > > >> I need to measure the time it takes signal to turn on and be at steady > >> state frequency (1 to 10MHz)to within 200hz resolution within 2us. The > >> kicker is that I can only sample at 65MSPS. Is this possible? I can > >> get 200hz resolution by sampling for 5ms, but I am only interested in > >> the sample from 0 to 2us, so when I window that section, I loose my > >> resolution. If this problem interests you, I can provide more > >> information on request. > >> > > > > The kicker isn't that you can only sample at 65 Msps, it's that you can > > only use 2 us of data. That constraint limits your resolution to 500 > > kHz, no matter what the sample rate is. > > Very wrong statement. > > There is absolutely no relation between the duration of the data and the > frequency resolution. The only thing that matters is the SNR. > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.comhttp://www.bores.com/courses/intro/basics/1_resol.htm
Reply by ●November 1, 20062006-11-01
Reply by ●November 1, 20062006-11-01
Randy Yates wrote:> Vladimir Vassilevsky <antispam_bogus@hotmail.com> writes: > > > John Sampson wrote: > > > >> alexs wrote: > >> > >>> I need to measure the time it takes signal to turn on and be at steady > >>> state frequency (1 to 10MHz)to within 200hz resolution within 2us. The > >>> kicker is that I can only sample at 65MSPS. Is this possible? I can > >>> get 200hz resolution by sampling for 5ms, but I am only interested in > >>> the sample from 0 to 2us, so when I window that section, I loose my > >>> resolution. If this problem interests you, I can provide more > >>> information on request. > >>> > >> The kicker isn't that you can only sample at 65 Msps, it's that you > >> can only use 2 us of data. That constraint limits your resolution to > >> 500 kHz, no matter what the sample rate is. > > > > Very wrong statement. > > > > There is absolutely no relation between the duration of the data and > > the frequency resolution. The only thing that matters is the SNR. > > I agree with Vladimir. > > Consider this gedanken. You have a pure sine wave that's been sampled and > input to a Hilbert transformer since the beginning of time. You select > two [complex] samples, 0*T and 1*T, from this infinite stream and compute > > f = (arctan2(x1.y/x1.x) - arctan2(x0.y/x0.x)) / T. > > This frequency is perfect with just two samples if there is no noise. > -- > % Randy Yates % "Though you ride on the wheels of tomorrow, > %% Fuquay-Varina, NC % you still wander the fields of your > %%% 919-577-9882 % sorrow." > %%%% <yates@ieee.org> % '21st Century Man', *Time*, ELO > http://home.earthlink.net/~yatescrYes, the instantaneous frequency. How long do I need to look at it for to know that the signal is within 200 Hz of steady state? John
