Quote:
Originally Posted by Stedy
Hi,
Looking at the PCB from Github, https://github.com/solarmon/RGBtoHDM...202%20-%20SOIC
I can see why you have issues.
1) You have a high speed, fast edge rate XOR gate, the 74LV84 has <1ns rise/fall times and 24mA drive. This is great for a 30cm motherboard, not so good for ~60mm PCB trace. You have tried some slower devices, with mixed results, the MC74VHCT86 from Onsemi would be a good fit but this is not all.
2) The PIClk signal is way too close to pixel data R0 and R1. You must keep clock signals at least 3x track width separation from other signals
3) A capacitor on Piclk helps but add an AC terminator (75-100R resistor) with the capacitor C6 and you'll remove the high frequency edges on the clock signal to the PI.
4) Either change C5 to 1206 size or provision for another 0805 capacitor. Small, high value ceramics really drop off with applied voltage. See https://pdfserv.maximintegrated.com/en/an/TUT5527.pdf. This will give a bit more margin for power supply noise.
These tweaks should clean up the signal traces and improve the picture. |
Actually, the pixel sparkles were experienced on the original c0pperdragon RGBtoHDMI v2 boards. These original boards have very poor mask clearances, which is what I believed to be the main cause, especially when there is flux residue contamination, along with bad soldering work.
My custom RGBtoHDMI SOIC based boards with the large chip package and larger pin pitch also really helps.
In fact, all of my custom RGBtoHDMI boards found at
https://github.com/solarmon/RGBtoHDMI don't seem to have any pixel sparkles issues from my testing - because I've made sure the mask clearances are better and the pin holes much smaller for the header pins, so that there is not much movement. I have used both VLC and VHC TSSOP chip packages and I don't have the issues that I had with the original c0pperdragon RGBtoHDMI v2 boards.