VGA Interface Resistance Network Impedance Matching

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VGA Interface Resistance Network Impedance Matching

Taking into account the cost-aware Implementation of the simple solution, with R-2R Resistance Network Analog DAC replacement adv7123 video conversion chip.

I thought this was just a simple partial pressure. The more information I read, the deeper I got, the more I learned:

First, let's take a look at several pictures of others and make a comparison.

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Amy

De1

Red hurricane

Pony

Myself, crazy bingo, today, to design a 16-bit real color R-2R conversion network, asked a lot of netizens, read a lot of information, think for a long time, I carefully read the documents of Jack Ma and drew the figure below. It is not verified. I still don't know if I can ......

Crazy Bingo

The VGA Interface Protocol stipulates that vga_r, vga_g, and vga_ B are red, green, and blue analog voltages, respectively, 0 ~ 0.714 v peak-peak (Peak-peak), 0 V indicates colorless, and 0.714v indicates full color.

The three-color source end and Terminal Matching resistance are both 75 ohm, as shown below:

Hsync and vsync synchronize row data without frame data, which is TTL level.

0.714 V is divided by the resistance pressure. As shown above, the parallel resistance on the left and the resistance on the right obtain 0 ~ The voltage range of 0.714 is shown as follows:

So I calculated the divider resistance as follows:

253.96 k | 1 k | 2 k | 4 k | 8 k | 16 K ≈ Ω

0.5k | 1 k | 2 k | 4 k | 8 K ≈ 258.06 Ω

(1) For vga_r/vga_ B:

Vmin = r/(R + 8k Ω) * 3.3v ≈ 0 V

Vmax = r/(R + 258 Ω) * 3.3 ≈ 0.714 v

Listen R ≈ 258*0.714/(3.3-0.714) ≈ 71.23 Ω

Bytes

V0 = r/(R + 8k Ω) * 3.3 V = 0.029 v

V4 = 0.714 v

(2) For vga_g:

Vmin = r/(R + 16k Ω) * 3.3v ≈ 0 V

Vmax = r/(R + 254 Ω) * 3.3 ≈ 0.7 V

Listen R ≈ 254*0.714/(3.3-0.714) ≈ 70.13 Ω

Bytes

V0 = r/(R + 16k Ω) * 3.3 V = 0.014 v

V5 = 0.714 v

I don't know if my idea is correct, but at least it is correct. The RGB interface resistance is probably about 70 Ω, which is the most suitable.

The most important problem is impedance matching. The source end has a 75Ω impedance, and the terminal also has a 75Ω impedance.

In this regard, I am the least ......

If the terminal impedance is not matched properly and the speed cannot be reached, how can we achieve 1024*768 * MHz ??

Both vga_hs and vga_vs are connected to the 75R resistor, which is the most source-end matching resistor.

In vga_r, vga_g, and vga_ B, A 20R resistor is added because the above resistance network is within the impedance range of 75R. This is something a netizen helped me calculate. I still don't know. I'm dizzy ......

Wait a few days. Let's make the board and test it with your own hands to see how it is best. If it doesn't work, we can skip the welding process, looking forward to my 16-bit RGB adapter ...... Ah

Be sure to understand impedance matching. This is too difficult and important ......