HDMI Redriver Retimer

William Schofield80

Other Parts Discussed in Thread: TMDS181, SN65DP159, SN75DP139, SN75DP159

I need to convert a 1.2V differential signal from a Xilinx FPGA to a 3.3V HDMI TMDS signal. It must also be able to achieve data rates above 3.4Gb/s per TMDS pair for my application. Will the TMDS181 work for my application. What is a HDMI retimer? What is a HDMI redriver?

www.ti.com/.../tmds181

over 8 years ago

0 Moises Garcia over 8 years ago

TI__Mastermind 23815 points

Hi William,

If your signal is AC coupled from FPGA, then you need a level translator SN75DP139 support the data rate you need, besides we have SN65DP159/SN75DP159 for HDMI 2.0

TMDS181 is just an HDMI redriver/retimer depending on data rate.
redriver -> receiver a weak signal and amplifies it
retimer -> regenerates input signal with a new clock, this cleans skew and jitter

Regards

0 William Schofield80 over 8 years ago in reply to Moises Garcia

Prodigy 100 points

Hi Moises,

I have read that a 100nF capacitor in an 0402 package is preferred for the AC coupling but is there a preferred dielectric that I should choose?

0 Moises Garcia over 8 years ago in reply to William Schofield80

TI__Mastermind 23815 points

Hi William,

100nF caps are required in AC coupled lines; regarding size and materials we use 0402 and 0201 mostly ceramic capacitors.

Regards

0 William Schofield80 over 8 years ago in reply to Moises Garcia

Prodigy 100 points

Hi Moises,

I am having difficulty understanding what I need to do with the control pins. It says in the datasheet linked below for the SNx5DP159 that the pin strap mode is available to configure the device if I2C is not available under section 9.2.1. Does this mean that if I2C is available I should not use the pin strap mode and set the I2C_EN/PIN to high for I2C control mode? What is pin strapping I have not heard the terminology before? Is there any advantage to using I2C over pin strapping?

www.ti.com/.../sn65dp159.pdf

0 Moises Garcia over 8 years ago in reply to William Schofield80

TI__Mastermind 23815 points

Hi William,

Pin strapping mode is juts GPIO mode to configure the device.

It dependce on what you want to do if GPIO or I²C is the configuration method you need.

using I²C gives you acces yo a wide range of configurations, using GPIO you can configure a few options.

It depends on your applications what you need to use GPIO or I²C.

Regards

0 William Schofield80 over 8 years ago in reply to Moises Garcia

Prodigy 100 points

Hi Moises,

Thank you for your explanation I now understand that pin strapping is just pulling the control pins high or low or leaving them floating. So if I enable the I2C bus by pulling the I2C_EN/PIN pin high can I leave the other control pins (16,17,23 & 34) in figure 30 floating as the pin strapping mode will be disabled?

0 Moises Garcia over 8 years ago in reply to William Schofield80

TI__Mastermind 23815 points

Hi William,

If you are using RSB package, you can left floated those pins.

Regards

0 William Schofield80 over 8 years ago in reply to Moises Garcia

Prodigy 100 points

Hi Moises,

I would like to ask you in figure 30 and 31 (www.ti.com/.../sn65dp159.pdf) why are there no 50 ohm termination resistors? But there are 50 ohm termination resistors in figure 4 of the following application note (www.ti.com/.../slla358.pdf).

Best regards,

William.

0 Moises Garcia over 8 years ago in reply to William Schofield80

TI__Mastermind 23815 points

Hi William,

DP159 is a DP++ tp HDMI level translator, that can be configures as DP retimer( www.ti.com/.../slla358.pdf ).
in DP++ to HDMI applications the termination resistors are on Video receiver device.
in DP retimer applications you need AC coupled signals, that's why you need to add termination resistors and AC capacitors.

Regards

0 William Schofield80 over 8 years ago in reply to Moises Garcia

Prodigy 100 points

Hi Moises,

Thanks for clarifying that I would also like to know why does the HDMI case have a 1M ohm resistor and 10nF capacitor in parallel attached to the HDMI receptacle? In figures 31 and 32 of the datasheet http://www.ti.com/lit/ds/symlink/sn65dp159.pdf

Best regards,

William.

0 Moises Garcia over 8 years ago in reply to William Schofield80

TI__Mastermind 23815 points

Hi William,

This is a common practice to connect chasis to GND.
Connecting the chasis directly to GND may have issues of EMI/RFI, ESD, and safety.

Regards

0 William Schofield80 over 8 years ago in reply to Moises Garcia

Prodigy 100 points

Hi Moises,

I have not been able to find the voltage rating of the capacitor connected to the chassis in the HDMI specification, what do you recommend?

Best regards,

William.

0 Moises Garcia over 8 years ago in reply to William Schofield80

TI__Mastermind 23815 points

Hi William,

You won't find this value in HDMI specification, this is a common practice to tie chassis to GND. Typical voltage rating for this capacitor is 2kV, however there are other approaches that tie chassis directly to GND.
You can choose the one that best fits your application.

Regards

0 William Schofield80 over 8 years ago in reply to Moises Garcia

Prodigy 100 points

Hi,

I can see that there are 4x 100nF capacitors that would be presumably be placed as close as possible to the pads 12, (19,20), 31 and 40. But what do I do with the 2x 10nF capacitors? I was under the impression that smaller value caps had to be placed the closest to the pads? Which pads do I need to place them near and why isn't there 4x 10nF capacitors or 1 10nF capacitor per pad (with the exception of 19,20 as they are adjacent)?

0 Moises Garcia over 8 years ago in reply to William Schofield80

TI__Mastermind 23815 points

Hi william,

10nF caps are there to reduce high frequency noise, one of those 10nF caps should be a typo of 100nF.
Thus, you would have 5x100nF for 5 Vdd pins, 10nF cap is just for the whole power supply just place it close to the device.

Regards

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