Reply by Jonathan Bromley●October 17, 20052005-10-17
On 17 Oct 2005 12:36:15 GMT, kd (pingboypulsar<spamoff>@hotmail.com)
wrote:
>Hopefully the interfacing to an external adc is not too complicated.
>
>I wish to be able to connect industrial sensor(s) to an adc, and
>then acquire the value to the fpga for further processing. Maybe its
>better to use an asic or something else for interfacing an adc. I
>need to find out these things.
So, where's the hard part?
You choose an external ADC based on the analog requirements -
sampling rate, precision, aperture jitter, analogue bandwidth,
and so on. You will probably find a lot of devices that meet
your needs, so you must then refine the choice based on
package size, cost, and complexity of the digital interface.
Since you are doing industrial sensing stuff, I guess the
data rate will be fairly low and it is probably sensible to
choose a device with a serial interface (SPI or similar)
because this will give you a smaller ADC package, use
fewer pins on the FPGA, and make the circuit board layout
much easier.
OK, now you start to read the ADC data sheet carefully
to decide what its digital data interface looks like.
Now you have a straightforward digital design problem
that can easily be solved in your FPGA. Use the FPGA
to generate the ADC's clock (probably divided-down from
your system clock), copy control register values out
to the ADC, and read conversion results back.
It's almost trivially easy. It would get harder
if any of the following conditions applies:
1) Sampling rate of any one ADC is greater than
about 50M samples/sec
2) Very large number of analogue inputs
3) Very high precision requirements (more than
about 14 bits)
4) Need to maintain some special timing relationship
between ADC sampling and something else, such as
the activity of a DSP device
Go away and try it. If you have trouble with some part,
come back here and I'm sure someone will try to help.
The rather vague nature of the responses so far has
been directly related to the rather vague nature of
your request :-)
--
Jonathan Bromley, Consultant
DOULOS - Developing Design Know-how
VHDL, Verilog, SystemC, Perl, Tcl/Tk, Verification, Project Services
Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, BH24 1AW, UK
Tel: +44 (0)1425 471223 mail:jonathan.bromley@doulos.com
Fax: +44 (0)1425 471573 Web: http://www.doulos.com
The contents of this message may contain personal views which
are not the views of Doulos Ltd., unless specifically stated.
Reply by pingboypulsar<spamoff>@hotmail.com●October 17, 20052005-10-17
Yes i wish to interface to an external adc.
Sorry if that was not clear.
Hopefully the interfacing to an external adc is not too complicated.
I wish to be able to connect industrial sensor(s) to an adc, and
then acquire the value to the fpga for further processing. Maybe its
better to use an asic or something else for interfacing an adc. I
need to find out these things.
Regards.
--
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