Time measurement with Xilinx Spartan-3 - Help

[mindy]

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Hi All

I need some help from someone that has worked with the Xilinx
Spartan-3 products.

I need to measure a "Time Of Flight" (TOF) of a laser pulse. The
measurement time will be between 6ns and 250ns. ( Ranges from 3-125
feet)

The system has two PIN sensors - One indicates the start of pulse
leaving the laser and the second receives the return pulse from the
reflection of the laser off the target.

I'm trying to avoid using ECL and TAC analog systems for this. I only
need 1ns resolution.

I have two ideas how to do this but don't know enough about the
Spartan-3 products to know if it will work.

1) Create Four 8-bit shift registers each running off a different
phase clock source (IE: 0-90-180-270) and run them at 250mhz.
All four would be feed by the same input signal. Then store
the data from the registers in the ram. I will need to de-interlace
the data.
Once the samples have been taken, go back any search the ram for the
edge of the return pulse.
This should give me a 1ns resolution in time for the samples.

How fast can a Spartan-3 shift data ?
Will this basic concept work ?
Is the clock/sampling jitter to large to expect separate input to
sample at this rate ?
etc ?

What is the Max shift rate of the Spartan-3 FPGA's ?

2) Create Four counters with each one running off a different phase
clock source (IE: 0-90-180-270) and run them at 250mhz.
Start the counter at the same time and stop them using the input
signal from the laser receiver signal.
Once they stop I will evaluate the 4 counter for the one with the
lowest value and determine the actual TOF from it.

Same basic question from above ?

Any other suggestions for making these type of measurements ?

Thanks
Mark

[Uwe Bonnes]

mindy <mi...@hotmail.com> wrote:

:
: ADVERTISEMENT
:
:
: Hi All

: I need some help from someone that has worked with the Xilinx
: Spartan-3 products.

: I need to measure a "Time Of Flight" (TOF) of a laser pulse. The
: measurement time will be between 6ns and 250ns. ( Ranges from 3-125
: feet)

...
: Any other suggestions for making these type of measurements ?

Look for a TDC, e.g. www.acam.de
--
Uwe Bonnes b...@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

[John_H]

"mindy" <mi...@hotmail.com> wrote in message
news:4cu3605e1vad3mjge...@4ax.com...
> ADVERTISEMENT

??
...

> I have two ideas how to do this but don't know enough about the
> Spartan-3 products to know if it will work.
>
> 1) Create Four 8-bit shift registers each running off a different
> phase clock source (IE: 0-90-180-270) and run them at 250mhz.

...
The shift registers and RAMs in the Spartan-3 can meet 250 MHz with margin.
There may be nuance (with both techniques) in the clock skew between the
phases that makes your error a bit more. Please note that sampling a start
with 1 ns resolution and a stop with 1ns resolution will give you +/- 1 ns
total error, not +/- 1/2 ns.
...

> 2) Create Four counters with each one running off a different phase
> clock source (IE: 0-90-180-270) and run them at 250mhz.

...
The counters can also run at 250 MHz without trouble. You need to be aware
of synchronization issues so you don't try to asynchronously sample a
counter value with your live signal - standard design techniques apply.
...

> Any other suggestions for making these type of measurements ?
>
> Thanks
> Mark

If you're into small production, consider the Virtex-IIPro (XC2VP2 is the
smallest) with the Rocket I/O giving you over 3 GHz sampling if you want it.
The additional cost will easily be offset by lower development costs and a
better measurement. You might be able to find a Virtex-IIPro seminar in
your area in the next few weeks where you can get the seminar and an XC2VP4
board for $150 US.

I'd go for sampling a sine/cosine analog signal pair with a dual-channel ADC
to get multi-picosecond resolution after converting angle to phase just
because it's fun.

- John_H

[Peter Alfke]

As John_H indicated, this job is easily done with the Multi-Gigabit
Transceiver in the smallest Virtex-IIPro device. Use the MGT as receive
only. Clock it with a reference frequency of 100 MHz, which via a built-in
PLL results in a 2 Gbps input sampling rate, i.e. a resolution of 0.5 ns.
Then read the 20-bit parallel side at 100 MHz and either store the words in
a BlockRAM for later casual evaluation, or convert the 20-bit code
on-the-fly into a binary number that you accumulate. A dual-ported 2k x 9
BlockRAM can do this conversion..
If you have questions, I can help. I am always interested in innovative and
unusual applications of our devices...

Peter Alfke, Xilinx
================================
> From: "John_H" <johnha...@mail.com>
> Organization: Xerox Officeprinting NewsReader Service
> Reply-To: "John_H" <johnha...@mail.com>
> Newsgroups: comp.arch.fpga
> Date: Wed, 24 Mar 2004 22:42:09 GMT
> Subject: Re: Time measurement with Xilinx Spartan-3 - Help

[Jim Granville]

Peter Alfke wrote:
> As John_H indicated, this job is easily done with the Multi-Gigabit
> Transceiver in the smallest Virtex-IIPro device. Use the MGT as receive
> only. Clock it with a reference frequency of 100 MHz, which via a built-in
> PLL results in a 2 Gbps input sampling rate, i.e. a resolution of 0.5 ns.
> Then read the 20-bit parallel side at 100 MHz and either store the words in
> a BlockRAM for later casual evaluation, or convert the 20-bit code
> on-the-fly into a binary number that you accumulate. A dual-ported 2k x 9
> BlockRAM can do this conversion..
> If you have questions, I can help. I am always interested in innovative and
> unusual applications of our devices...
>
> Peter Alfke, Xilinx
> ================================

Sounds a good idea. Any numbers on the Jitter and Apertures of the MGT,
as the OP may be able to take multiple readings to get even finer
resolutions. ( similar to the vernier principle, if you can control
phase creep accurately, or just statistical if you can vary phase in
a more random manner )
-jg