Hello I must sample 4 analog signals, and I must ideally sample them at the same time. And I'm going to down sample the data rate later. The sampling frequency at the ADC is 10 kHz and afterwards the signal gets LP filtered to 50 Hz bandwidth before down sampling to 200 Hz rate. But what happens if I use a muxed ADC. The last channel is always sampled later than the first channel. Could I reduce the channels like this instead: 1 2 3 4 2 3 4 1 3 4 1 2 4 3 2 1 and then restart the sequence again. Then the sampling latency gets divided between the channels. Is this a better solution?
Want to sampel 4 channels at the same time
Started by ●December 1, 2006
Reply by ●December 1, 20062006-12-01
Hello I must sample 4 analog signals, and I must ideally sample them at the same time. And I'm going to down sample the data rate later. The sampling frequency at the ADC is 10 kHz and afterwards the signal gets LP filtered to 50 Hz bandwidth before down sampling to 200 Hz rate. But what happens if I use a muxed ADC. The last channel is always sampled later than the first channel. Could I sequence the channels like this instead? 1 2 3 4 2 3 4 1 3 4 1 2 4 1 2 3 and then restart the sequence again. Then the sampling latency gets divided between the channels. Is this a better solution? (posted again,, had some errors in the first posting)
Reply by ●December 1, 20062006-12-01
Ben wrote:> Hello > > > > I must sample 4 analog signals, and I must ideally sample them at the same > time. And I'm going to down sample the data rate later. The sampling > frequency at the ADC is 10 kHz and afterwards the signal gets LP filtered to > 50 Hz bandwidth before down sampling to 200 Hz rate. > > > > But what happens if I use a muxed ADC. The last channel is always sampled > later than the first channel. > > > > Could I sequence the channels like this instead? > > > > 1 2 3 4 > > 2 3 4 1 > > 3 4 1 2 > > 4 1 2 3 and then restart the sequence again. > > > > Then the sampling latency gets divided between the channels. > > > > Is this a better solution? > > > > (posted again,, had some errors in the first posting) > >The only way I know to get simultaneous sampling is to use multiple ADCs driven by the same clock. John
Reply by ●December 1, 20062006-12-01
Ben wrote:> Hello > > > > I must sample 4 analog signals, and I must ideally sample them at the same > time. And I'm going to down sample the data rate later. The sampling > frequency at the ADC is 10 kHz and afterwards the signal gets LP filtered to > 50 Hz bandwidth before down sampling to 200 Hz rate. > > > > But what happens if I use a muxed ADC. The last channel is always sampled > later than the first channel. > > > > Could I sequence the channels like this instead? > > > > 1 2 3 4 > > 2 3 4 1 > > 3 4 1 2 > > 4 1 2 3 and then restart the sequence again. > > > > Then the sampling latency gets divided between the channels. > > > > Is this a better solution?First, make sure that a multiplexer will work. It will always have some settling time, but the intractable problem may be the ADC. How much time does yours need after being connected to a signal before it starts to deliver accurate conversions? For some ADCs, it is many sample times. Even if the multiplexer and ADC combination works for you, each channel will need its own anti-alias filter. The settling time of an effective filter will surely exceed the sample time of a single channel. Are you sure that you need to sample simultaneously? Properly bandlimited samples represent the signal unambiguously at all instants; that's what makes reconstructing the analog signal possible. The decimating that you plan to do down the processing chain allow you to align the sample in time by choosing which ones to keep and which to discard. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 1, 20062006-12-01
Ben wrote:> Hello > > > > I must sample 4 analog signals, and I must ideally sample them at the same > time. And I'm going to down sample the data rate later. The sampling > frequency at the ADC is 10 kHz and afterwards the signal gets LP filtered to > 50 Hz bandwidth before down sampling to 200 Hz rate. > > > > But what happens if I use a muxed ADC. The last channel is always sampled > later than the first channel. > > > > Could I sequence the channels like this instead? > > > > 1 2 3 4 > > 2 3 4 1 > > 3 4 1 2 > > 4 1 2 3 and then restart the sequence again. > > > > Then the sampling latency gets divided between the channels. > > > > Is this a better solution?Hello Ben, Thisis not a new problem. http://www.google.com/search?hl=en&q=sample+and+hold+circuit Good Luck donald
Reply by ●December 1, 20062006-12-01
Ben wrote:> Hello > > I must sample 4 analog signals, and I must ideally sample them at the same > time. And I'm going to down sample the data rate later. The sampling > frequency at the ADC is 10 kHz and afterwards the signal gets LP filtered to > 50 Hz bandwidth before down sampling to 200 Hz rate.You can build the appropriate delay into the downsampling filters to time-align the four channels. Is that an option? Regards, Andor
