Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:Yes, depending on the application that may be OK. But note the kink in the centre, that's more than likely the the MSb output resistor being slightly off.
Steve Anderson wrote:If you have a circuit simulator you can see the effect of resistor tolerance on the output voltage. Say using a R2R ladder comprised of 10k and 20k resistors, all exact except one. The degree of influence does depend on where in the ladder the 'off'' resistor is, but it is an error. And in practice it's not just one resistor.
For 12-bits you're hoping for an accuracy of 1/4096, about 0.025%.
Steve A.
Steve Anderson wrote:I feel what needs to be pinned down is the modes this multi-standard monitor needs to work at. How many lines maximum at the maximum frame/field rate.
If you want to go (say) for 256 lines at 50Hz non-interlaced that's a line rate of 12.8kHz. Now if the picture was square, and ignoring syncs, blanking and the like the pixel rate is about 3.3MHz. This would also be the line timebase clock rate. In practice it would have to be 20-30% higher, even more so if using a 4:3 aspect ratio.
Klaas Robers wrote:You can try the IC DAC8. It is an integrated ladder network for 8 bits. and the irregularity at 127 to 128 is almost invisible on an oscilloscope.
For the horizontal sawtooth you think that you need many bits to make the wave form smooth, but with a small capacitor you can smooth the fine staircase to a sawtooth. Then the jump back is slightly slower, but all TV standards have a kind of sync pulse at that moment, so you wouldn't see it. It is blanked!
For the vertical sawtooth this is not needed, a staircase is even better than a sawtooth. Also the jump back is done instantaneous, much faster than with whatever sawtooth. And don't be afraid for higher frequencies. Your limit is the max. clock frequency of the 4040.
Steve Anderson wrote:I used a DAC08 in the NBTV/SSTV-625 up-converter for the video output. It has enough bandwidth. It's downside is it requires + and - supplies, otherwise it's very easy to use.
Attached is a partial of the circuit of the MkI version (the MkIII is virtually identical). Ignore the AND gates, a few minor changes would be required here and there for your application. The supplies don't have to be +/-12V, +/-5V would be OK too. In fact they don't have to be equal, say +12V and -5V.
Steve A.
That damned default font....but it should give the idea.
Not heard of Tesla before, not at least relating to chips. But at the price it's worth taking a chance. I'm fairly confident they'll be OK. The type numbering differences are almost superficial, most of these devices are the same, just a slightly different specification.
I did a search for the company and came up with two, one in Europe the other in Bangladesh. Nether appear to have a web-site.
If you do go ahead perhaps you could send me a couple and I'll drop them into the NBTV/SSTV-625 up-converter and confirm they're OK.
I agree, the differences between the type numbers can be confusing, sending you off for hours trying to find out if there are any significant differences. But without a Tesla datasheet we'll just have to try them out.
Steve A.
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