09-03-2023, 02:52 PM
I encouraged Darryl to do the 405 NTSC version of Aurora. The design isn't difficult, but it does use a lot more FPGA resources. Darryl had to use a bigger FPGA that fitted on the same footprint as the original. Roughly speaking, it needs twice as much memory (to store chroma as well as luma), several multipliers to do the coding and some other logic such as a subcarrier generator, adders etc. Not a hope with the Lattice version of Hedghog which is already pushing the limits of the device.
Coding NTSC from 405 RGB is easier to do in analogue. A couple of 1496 balanced modulators, the right frequency crystal (4xfsc for NTSC 405), handful of video opamps. The problem with doing it in an FPGA is you have to digitise the RGB separately. The standard PAL/NTSC decoders don't do this.
Block diagram and schematics of an analogue PAL coder I designed for G2 Systems in 1986/7. My first proper project when I went freelance. Desinged to code the output of a BBC micro. It predates low cost video opamps. Easily modified for NTSC (I've done NTSC 525). I still have the handwired prototype and it still works. A production version is coding the RGB output of the COW rotating BBC globe at the Dulwich museum.
Coding NTSC from 405 RGB is easier to do in analogue. A couple of 1496 balanced modulators, the right frequency crystal (4xfsc for NTSC 405), handful of video opamps. The problem with doing it in an FPGA is you have to digitise the RGB separately. The standard PAL/NTSC decoders don't do this.
Block diagram and schematics of an analogue PAL coder I designed for G2 Systems in 1986/7. My first proper project when I went freelance. Desinged to code the output of a BBC micro. It predates low cost video opamps. Easily modified for NTSC (I've done NTSC 525). I still have the handwired prototype and it still works. A production version is coding the RGB output of the COW rotating BBC globe at the Dulwich museum.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
