Impedance control of DM8168 VGA output

Hello,

I am not expert on this but you could check :

http://www.ti.com/product/THS7360

http://www.ti.com/general/docs/datasheetdiagram.tsp?genericPartNumber=THS7360&diagramId=SLOS674

Best Regards,
Margarita

Thinks for your enthusiastic reply. As DM8168's VGA output is current output and I'm not sure whether it need impedance control.

Hello,

I will forward it to our experts.

Best Regards,
Margarita

Eli,

Eli Wang said:

As DM8168's VGA output is current output and I'm not sure whether it need impedance control.

Could you please provide us more details regarding your definition of "VGA output"? Is "VGA output" actually the DM816x Digital Video Output Signals? Or Analog Video Output Signals? Or else?


Regards,
Pavel

Hi，

 DM8168's VGA output means the Video  Analog HD Video DAC（pinAT21 AR21 AP21） ：）

Thinks a lot！

Eli,

Eli Wang said:

DM8168's VGA output means the Video  Analog HD Video DAC（pinAT21 AR21 AP21）

These are Analog Video Output Signals (see DM816x datasheet, section 4.2.21)

IOUTA - AT21 - Video DAC A output. Analog HD Video DAC (G/Y)
IOUTB - AR21 - Video DAC B output. Analog HD Video DAC (B/Pb)
IOUTC - AP21 - Video DAC C output. Analog HD Video DAC (R/Pr)

Regarding your question, from what I understand, you need to know if you should place 75ohm resistors on these output lines (AT21, AR21, AP21). If this is your question, then my answer is yes, you should have 75ohm resistors attached on these output lines (AT21, AR21, AP21).

See DM816x datasheet, section 9.10.2 Video DAC Guidelines and Electrical Data and Timing

Place the 75-Ω resistor as close as possible (<0.5") to the amplifier or buffer (THS7360) output pin.


See also the DM816x TI EVM schematics:

Regards,
Pavel

Hi，Pavel
Maybe I didn't express clearly.I wanna know if the line on the PCB between DM8167 pinAT21 AR21 AP21 and THS7360 need Impedance control.My schmetic is the same as DM816x TI EVM. What puzzled me is the Impedance control in PCB layout. : )If we need to control the impedance,what's the exact controlled impedance?37.5Ohm or 75 Ohm?

Regards,
Eli