UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - New Multi-Standards Converter / Convertor Design Discussion

ppppenguin · 29th Jul 2004, 4:19 pm

You execute the standard coder equations.

1. LPF the Cb and Cr components. Simple 1/4 + 1/2 +1/4 FIR is about right
2. Scale them according to the PAL or NTSC weighting factors. Now you have U and V
3. Multiply them by subcarrier (with 90 degree phase difference. And PAL switch if needed)
4. Add them together
5. Scale the Y.
6. Add Y to modulated C

Since the clock rate will be several times the Cb/Cr sample rate you can save a lot of multipliers.

Subcarrier is generated by an adder/accumulator and a sine lookup table. Reset the accumulator every 4 or 8 fields if you want absolutely correct SCH phase. 90 degree and 180 degree phase switching are simple to do ahead of the sine table.

Burst and sync edge shapes are pre-calculated and stored in small ROMs.

Burst is modulated along with Cb and Cr in the same multiplier(s). May be easier to do PAL burst modulation in just one multiplier rather than separate U and V components. This means phase shifting the subcarrier by 45 degrees. This is how I did my colour black.

Don't ask me how to do SECAM coding! I don't want to go there. Actually I do know a little about SECAM, having worked for Michael Cox Electronics many years ago. Mike was a great SECAM enthusiast.

29th Jul 2004, 4:19 pm	#11
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: New Multi-Standards Converter You execute the standard coder equations. 1. LPF the Cb and Cr components. Simple 1/4 + 1/2 +1/4 FIR is about right 2. Scale them according to the PAL or NTSC weighting factors. Now you have U and V 3. Multiply them by subcarrier (with 90 degree phase difference. And PAL switch if needed) 4. Add them together 5. Scale the Y. 6. Add Y to modulated C Since the clock rate will be several times the Cb/Cr sample rate you can save a lot of multipliers. Subcarrier is generated by an adder/accumulator and a sine lookup table. Reset the accumulator every 4 or 8 fields if you want absolutely correct SCH phase. 90 degree and 180 degree phase switching are simple to do ahead of the sine table. Burst and sync edge shapes are pre-calculated and stored in small ROMs. Burst is modulated along with Cb and Cr in the same multiplier(s). May be easier to do PAL burst modulation in just one multiplier rather than separate U and V components. This means phase shifting the subcarrier by 45 degrees. This is how I did my colour black. Don't ask me how to do SECAM coding! I don't want to go there. Actually I do know a little about SECAM, having worked for Michael Cox Electronics many years ago. Mike was a great SECAM enthusiast.