With current A/D technology, what is the upper limit of what can be directly sampled? Super-nyquist is OK -- I'm wondering about the highest absolute frequency that can be directly sampled in any practical sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA antenna? How high can you go?
A/D Practical Aperture Limit
Started by ●September 18, 2007
Reply by ●September 18, 20072007-09-18
Jon Mcleod wrote:> With current A/D technology, what is the upper limit of what can be > directly sampled?Maxim has A/D converters with BW 2.2GHz and sample rate to 1.5GHz.> Super-nyquist is OK -- I'm wondering about the > highest absolute frequency that can be directly sampled in any practical > sense.In any practical sense it is not recomended to use Maxim parts.> Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA > antenna?Sure you can, but it is not going to be very useful. The SINAD is only 45dB or so. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●September 18, 20072007-09-18
On Tue, 18 Sep 2007 20:28:09 -0400, Jon Mcleod <jonmcleod2003@yahoo.com> wrote:>With current A/D technology, what is the upper limit of what can be >directly sampled? Super-nyquist is OK -- I'm wondering about the >highest absolute frequency that can be directly sampled in any practical >sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA >antenna? How high can you go?How high do you want it to go? How much do you want it to cost? Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by ●September 19, 20072007-09-19
One problem is timing jitter: A given sampling time offset (in seconds) leads to an error voltage that is proportional to dV/dt, where V is the signal voltage. Naturally, dV/dt increases proportionally with the signal frequency. This can hurt subsampling schemes badly, because the resulting error may appear as white noise over the whole bandwidth: The smaller the bandwidth-to-signal ratio, the more jitter-related noise folds inband and hits the signal. Cheers Markus
Reply by ●September 19, 20072007-09-19
Jon wrote:> With current A/D technology, what is the upper limit of what can be > directly sampled? Super-nyquist is OK -- I'm wondering about the > highest absolute frequency that can be directly sampled in any practical > sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA > antenna? How high can you go?Theoretically, sampling only requires a finite band, not necessary lowpass bandlmitation. So if you are sampling with frequency Fs, you can perfectly reconstruct a signal that lies in the interval [k Fs/2, (k+1) Fs/2] for any k in {0, 1, 2, ... }, provided you know k. Note that there is no upper limit on k. Regards, Andor
Reply by ●September 19, 20072007-09-19
On Sep 19, 2:29 am, Andor <andor.bari...@gmail.com> wrote:> Jon wrote: > > With current A/D technology, what is the upper limit of what can be > > directly sampled? Super-nyquist is OK -- I'm wondering about the > > highest absolute frequency that can be directly sampled in any practical > > sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA > > antenna? How high can you go? > > Theoretically, sampling only requires a finite band, not necessary > lowpass bandlmitation. So if you are sampling with frequency Fs, you > can perfectly reconstruct a signal that lies in the interval > > [k Fs/2, (k+1) Fs/2] > > for any k in {0, 1, 2, ... }, provided you know k. Note that there is > no upper limit on k. > > Regards, > AndorPractically, however, the input frequency response of the A/D converter will diminish enough to impose some limit on what k you can actually achieve. For signals at too high of a frequency, there's not enough time for the input capacitance on the converter to charge/ discharge to the right voltage before it's sampled! Stupid analog electronics and their parasitics. Jason
Reply by ●September 19, 20072007-09-19
On 19 Sep., 15:37, cincy...@gmail.com wrote:> On Sep 19, 2:29 am, Andor <andor.bari...@gmail.com> wrote: > > > > > > > Jon wrote: > > > With current A/D technology, what is the upper limit of what can be > > > directly sampled? Super-nyquist is OK -- I'm wondering about the > > > highest absolute frequency that can be directly sampled in any practical > > > sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA > > > antenna? How high can you go? > > > Theoretically, sampling only requires a finite band, not necessary > > lowpass bandlmitation. So if you are sampling with frequency Fs, you > > can perfectly reconstruct a signal that lies in the interval > > > [k Fs/2, (k+1) Fs/2] > > > for any k in {0, 1, 2, ... }, provided you know k. Note that there is > > no upper limit on k. > > > Regards, > > Andor > > Practically, however, the input frequency response of the A/D > converter will diminish enough to impose some limit on what k you can > actually achieve. For signals at too high of a frequency, there's not > enough time for the input capacitance on the converter to charge/ > discharge to the right voltage before it's sampled! Stupid analog > electronics and their parasitics.^Are you saying that A/D converters don't generate a train of dirac impulses for sampling? :-)
Reply by ●September 19, 20072007-09-19
On Sep 19, 11:58 am, Andor <andor.bari...@gmail.com> wrote:> On 19 Sep., 15:37, cincy...@gmail.com wrote: > > > > > On Sep 19, 2:29 am, Andor <andor.bari...@gmail.com> wrote: > > > > Jon wrote: > > > > With current A/D technology, what is the upper limit of what can be > > > > directly sampled? Super-nyquist is OK -- I'm wondering about the > > > > highest absolute frequency that can be directly sampled in any practical > > > > sense. Could I directly sample a 900MHz GSM antenna? Or a 1.8G CDMA > > > > antenna? How high can you go? > > > > Theoretically, sampling only requires a finite band, not necessary > > > lowpass bandlmitation. So if you are sampling with frequency Fs, you > > > can perfectly reconstruct a signal that lies in the interval > > > > [k Fs/2, (k+1) Fs/2] > > > > for any k in {0, 1, 2, ... }, provided you know k. Note that there is > > > no upper limit on k. > > > > Regards, > > > Andor > > > Practically, however, the input frequency response of the A/D > > converter will diminish enough to impose some limit on what k you can > > actually achieve. For signals at too high of a frequency, there's not > > enough time for the input capacitance on the converter to charge/ > > discharge to the right voltage before it's sampled! Stupid analog > > electronics and their parasitics.^ > > Are you saying that A/D converters don't generate a train of dirac > impulses for sampling? > > :-)Oh no, don't get that can of worms open again! Jason
Reply by ●September 20, 20072007-09-20
cincydsp@gmail.com wrote:> ... Stupid analog electronics and their parasitics.Welcome to the real world, where all engineering starts and ends. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●September 20, 20072007-09-20
Andor wrote: ...> Are you saying that A/D converters don't generate a train of dirac > impulses for sampling?No Diracs and -- get ready for this, are you sitting down? -- there are no tooth fairies, either. :-) Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
