On 3/18/06, James Richard Tyrer <[EMAIL PROTECTED]> wrote: > > Timothy Miller wrote: > > On 3/17/06, Jack Carroll <[EMAIL PROTECTED]> wrote: > >> On Thu, Mar 16, 2006 at 09:27:40PM -0700, James Richard Tyrer wrote: > >>> No, if you are trying to display square pixels, the rise time is > >>> important. > >>> > >> And displaying square pixels is _really_ important. We can't get a > >> fair evaluation of OGA without that. > > > > Understood. But I think we'll have bandwidth that exceeds the 3rd > > harmonic anyhow. > > > We are talking about the HiRes head here. > > I hope that I now have this correct. The pixel rate is 500 MHz so the > maximum fundamental video frequency is 250 MHz and the 3rd harmonic is > then 750 MHz. The frequency response should be basically flat to 750 MHz.
This is something I don't understand all that well. But I believe that it is 500 million pixels per second. In order to have reasonably good pixels, the bandwidth has to be higher than that. > > So, if we intend to have 500 MHz dot clock frequency, the video buffer > amps do not really have enough bandwidth with a gain of 2. The ths3201 > spec is 850 MHz -3dB. This could be improved by increasing the input > current of the DAC and reducing the gain of the amp. We're probably going to have to do that tweak. > With a current feedback amp, you can also do peaking by reducing the > value of the feedback resistor slightly. > > However, it appears that the Burr Brown OPA695 would be a better choice > for a gain of 2 -- the spec is 1.4 GHz -3 dB. > > We could do a better by running with a gain of 1 and differential input. > This is what is recommended for the DAC. But, this is problematic > with a current feedback amp. I'll defer to Howard on this. :) _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
