Anti-aliasing advice for de-interleaved signals
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From: PhilipOrr on 23 Jul 2010 04:47 Many thanks again for your thoughts. Fred - yes, your model is correct I think. That's what's happening. The more you all explain this the more the scheme seems pointless! So basically, unless I have some strong common-mode signals I want to reduce, there is no use to the subtraction because it will only improve my SNR by a factor of 1.414, because the random noise increases. Maybe instead I should try something like driving the switch like a modulator at fswitch << sample rate, and then use something like a lock-in amp to get the signal power at fswitch, using the switch driving signal as the lock-in reference. It would take more development but frankly now the differential scheme seems pretty silly. Philip
From: Jerry Avins on 23 Jul 2010 10:43 On 7/23/2010 4:47 AM, PhilipOrr wrote: > Many thanks again for your thoughts. Fred - yes, your model is correct I > think. That's what's happening. > > The more you all explain this the more the scheme seems pointless! So > basically, unless I have some strong common-mode signals I want to reduce, > there is no use to the subtraction because it will only improve my SNR by a > factor of 1.414, because the random noise increases. > > Maybe instead I should try something like driving the switch like a > modulator at fswitch<< sample rate, and then use something like a lock-in > amp to get the signal power at fswitch, using the switch driving signal as > the lock-in reference. It would take more development but frankly now the > differential scheme seems pretty silly. Whatever scheme you finally hit on will have far better success if you identify the major noise mechanism. It is nearly futile to try to mitigate a problem you know little about. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: Michael Plante on 26 Jul 2010 00:45 Jerry wrote: >On 7/21/2010 8:12 PM, PhilipOrr wrote: >> Hi everyone - this is my first post here. It's about time I joined a DSP >> forum. >> >> I need some advice related to a measurement system. The system samples at 1 >> kHz but between every sample the input to the DAQ is switched between two >> inputs. The result is that the acquired signal, at 1 kHz, is two >> interleaved signals at 500 Hz each. >> > >...that precedes ADC. (You wrote DAC, but I don't think you meant >that.) ... Perhaps a nitpick, but he wrote DAQ, not DAC, and I've seen that in the context of Labview/NI to mean "Data AcQuisition unit". I.e., a packaged ADC. That term threw me off a bit too when I first heard it, because it is pronounced like "DAC", but really means "ADC". Fun stuff...
From: PhilipOrr on 26 Jul 2010 11:48 >Perhaps a nitpick, but he wrote DAQ, not DAC, and I've seen that in the >context of Labview/NI to mean "Data AcQuisition unit". I.e., a packaged >ADC. That term threw me off a bit too when I first heard it, because it is >pronounced like "DAC", but really means "ADC". Fun stuff... Yep, sorry for the confusion. I wrote DAQ deliberately to mean data-acquisition not DAC. Must be a LabVIEW term only.
From: Jerry Avins on 26 Jul 2010 14:17
On 7/26/2010 12:45 AM, Michael Plante wrote: > Jerry wrote: >> ...that precedes ADC. (You wrote DAC, but I don't think you meant >> that.) ... > > Perhaps a nitpick, but he wrote DAQ, not DAC, and I've seen that in the > context of Labview/NI to mean "Data AcQuisition unit". I.e., a packaged > ADC. That term threw me off a bit too when I first heard it, because it is > pronounced like "DAC", but really means "ADC". Fun stuff... Thanks for the heads-up. I apologize to P.O. for my poor reading. Jerry -- Engineering is the art of making what you want from things you can get. ����������������������������������������������������������������������� |