nospam wrote:

>
> Some time ago I did some experimentation (for a very cost sensitive
> application) with a Spartan 3 part using an LVDS differential input as a
> voltage comparator for a crude delta sigma ADC.
>
> The I/O bank Vcco was 3.3v the common mode on the LVDS inputs was half the
> 3.3v supply and the differential input voltage was (obviously) limited to
> whatever it took drive the LVDS input one way or the other.
>
> It worked fine.
>
> Now the customer says he wants to use Cyclone II.
....

> Can anyone confirm this and has anyone experience of using LVDS inputs as
> voltage comparators on Cyclone II (or Spartan 3/3e for that matter).

I have a bunch of Cyclone I and II designs using LVDS based at 1.65V that
are working just fine at 270MHz input rate. They are fed by either Gennum
9064 or CYV270M0101EQ cable equalizers (I prefer the Cypress, but it has
only just become available in volume).

I remember from my Altera days that there was some reference-ish design that
used the same trick to make an LVDS pair act as a Digta-Selma (or the other
way round) ADC. It had horrible DC properties, but at frequencies over
100Hz it was fairly accurate (16 bit up to 250KHz or so).

Best regards,


Ben