> 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
Reply by Donald●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
>
>
>
> 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.
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Reply by John Sampson●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 Ben●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 Ben●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 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?