Re: FPGA NTSC signal with 2 resistors and PWM

On Sep 28, 10:34 am, Antti <Antti.Luk...@xxxxxxxxxxxxxx> wrote:
Hi

I am evaluating the possibility to use 2 resitor video output from
FPGA similar to:

http://www.excamera.com/articles/15/ntsc.html

to generate color NTSC output, so far my results show less quality
then the test picture in the link above
I use 300/600 ohm with Xilinx Spartan3A starterkit

I am not yet sure if the difference in visible output is from the
different receiver USB video grabber vs TV receiver, but the video as
grabbed with cheap 25EUR grabber is very noisy, almost like the 80MHz
would be pass the input filtering so that the 16 shaders are almost
not recognizeable, also there is too much noisy flickering at the top
the screen. I will be testing with real TV set later, so I can compare
better.

so just asking if anyone has any compare results or suggestions for
ultra low cost and simple direct video output with FPGA, there is one
design with 9 resistors and 2 bipolar transistors, or then R-2R type
networking, both are too complex, if a PWM based solution could work
with some little neat tricks

Antti


A television will have a low-pass filter on the video and may look
better. If you didn't add at least a capacitor (1 pole LPF) after
your PWM, the digital grabber will no doubt show the effects of
sampling the 80 MHz PWM signal.

Noise at the top of the screen may indicate some problem with
sync levels. My guess is that a proper LPF might fix this, too.

Good luck,
Gabor

.

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