vga signal amplifier

[ronsimpson]

I would use a current feed back amp like the LMH6720. It is not like a voltage feed back "op-amp".
OR
Here is a two transistor amp, using general purpose transistors. Good for 100mhz.

 

[ronsimpson]

The 50 ohm resistors need to be 75 ohms.
Rf needs to be slightly larger than 300 ohms to get gain above one.

 

[AnalogKid]

Here is a two transistor amp, using general purpose transistors. Good for 100mhz.

How is the low frequency response? For true chroma clarity, it needs to be gain and phase flat down to 15 Hz for NTSC.

ak

 

[ronsimpson]

How is the low frequency response? For true chroma clarity, it needs to be gain and phase flat down to 15 Hz for NTSC.

I don't understand why 15hz. The DC is being reestablished at 48khz or what ever the horizontal rate is. Yes I don't want slope to the video (with in a line) but I can see that in old TV sets. I set the amp to be -2db at 100hz. If the video low frequency response caused one line of video to drop less then 1/256 then the problem would be hard to detect. I don't want to do the math but if there is now -2db in 100hz then what is the drop in 48,000hz? That would be the error in intensity from left to right over one line. Then we reset the DC level for the next line. There would be no low frequency problem vertically because of DC restoration.

 

[AnalogKid]

In NTSC, the horizontal line rate is 15.750 kHz for a pure mono signal, and 15.734 kHz for color. This is the rate at which a sync tip or back porch clamp restores the DC level of the signal. The monochrome vertical field rate is 59.94 fields per second, and the frame rate is 29.97 interlaced frames per second. This is why 30 Hz usually is cited as the lowest frequency of interest in NTSC video. It is 25 Hz for PAL.

However, there are 262.5 horizontal lines per field, and 227.5 cycles of chroma subcarrier per line, for a total of four chroma fields, two per monochrome field, so chroma-phase-aligned editing can take place in only 15 places per second. A spectrum analyzer display of an NTSC color signal shows a narrow spike at approx. 15 Hz.

ak

 

[ronsimpson]

Yes, and this thread is about VGA.
There is no 15,750. No 29.97. No Chroma subcarrier. No 15hz spike.

 

[AnalogKid]

I lost sight of that late at night. Plus, I like old video...

ak