Re: FPGA Journal Article

Jim, beware, you are hitting a hot-button !
Jim Granville wrote:
>> Digits of precision & granularity ?
10 decimal digits fixed-point display, but 2 ppm accuracy.
Above 1 MHz limited by time base accuracy, below 1 MHz by display
(just because we are too lazy to make the display floating point...)
>
> > A tad outside the average hobbiest resource pool ?
I think so.
> >
> Yes, scopes are dominated by things other than the FPGA, so are not
> ideal demo-examples.
Yes and no. For low-performance, most complexity would be in FPGA,
DRAM, and PC.
>
> My favourites would be for Xilinx to do a split
> a) Freq Ctr & Signal Generator - Smallest/Cheapest FPGA version
Wait for the S3Eeval board. It includes a freq.gen design based on my
box. Ken Chapman did the control for both of them (PicoBlaze-based), so
you can be convinced it is good.
But it only goes to 80 MHz (?) and the jitter may be more than 100 ps,
since he has no PLL to clean it up further.
>
> b) Freq Ctr & Signal Generator - Money-no-object version
I am going for 2.5 GHz square wave, 1 Hz resolution, and lowest jitter.
But no arbitrary function, adjustable amplitude or duty cycle. All
those things are possible, but clutter up the design. Maybe there will
also come a USB-controlled derivative that offers more freedom.

Please tell me what people need a frequency counter for. I have thought
of a design for years, including reciprocal counting at low frequency
for high resolution with short capture time. But it died for lack of
interest. We could of course include something in the S3E eval board.
>
> FreqCtr's can become quite complex - so a series of designs would show
> users more and more, but still have a HW platform that is
> i) FPGA dominated
> ii) Clearly ahead of any uC alternative
The S3E eval board accuracy will be limited by its 50 ppm xtal, and the
resolution might be pushed to almost 1 GHz. Display is no problem @ 2 x
16 digits.
A 20 times more accurate time base would cost <$20 extra.
I warned you, this is a hot button with me.
My thesis project, looong ago, was a frequency counter. It's deep in my
genes.
Peter

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