DS90UB914 Eq settings

Randy Luck

Hi-

We are using the DS91UB913A and DS90UB914A. My questions have to do with discrepancies in the register settings for the Eq gain that I see between the '914A datasheet, the '914Q datasheet, an E2E forum post, and what I actually observe on our system. The E2E forum post I mention can be found at http://e2e.ti.com/support/interface/high_speed_interface/f/138/t/350587.aspx

The '914 register located at 0x04 is the EQ Feature Control register and the '914 register located at 0x4E is the EQ Value register. As I understand it, the chips power up defaulted to use the Auto Equalization feature. The 0x4E register can be used by firmware to see what the Eq gain is set to. So by reading register 0x4E, you can see what the auto eq function has set the gain to. The auto equalization feature can be turned off and manual control of the eq gain can be done by writing a 0x40 to the AEQ Test Mode Select register at 0x4D. Then you can manually control the eq gain by writing to the EQ Feature Control Register at 0x04.

If you look at the '914A datasheet there is obviously a typo in the description for the 0x04 register on page 33. The forum link above asks about the same typo and attempts to correct it. If you look at the description for the 0x4E register on page 40 you will see that it shows 5 possible gain settings that can be read. If I understand what it is saying, these gains are read as 0x0F, 0x1F, 0x3F, 0x7F, and 0xFF.

Now looking over at the '914Q datasheet, you see a different description for these registers. This doesn't make sense because as I understand it the 'A and 'Q parts are essentially the same except that the 'A parts allow either a coaxial or differential serial link to the '913 while the 'Q parts only offer the differential link. The description for the 0x04 register on page 29 shows 7 possible settings of 0x00, 0x01, 0x03, 0x07, 0x0F, 0x1F, and 0x3F. Looking over at the description for the 0x4E register on page 36 it just says reads back the adaptive and manual equalization value.

So my question is what is correct? By observation of my '913A and '914A system, I see that the Auto Eq feature is actually setting register 0x4E to more possible values than the 'A data sheet (or the forum posting) shows. As a matter of fact, I believe that all the values from both datasheets are possible, at least on my '914A system.

Something like this:

0x00 0dB |

0x01 4.5dB |

0x03 6.5dB | According

0x07 7.5dB | to '914Q

0x0F 8dB | datasheet |

0x1F 11dB | | According

0x3F 12.5dB | | to '914A

0x7F 14dB | datasheet

0xFF 16dB | and previous forum link

Is this correct?

Several other questions...

Are the Eq gain settings shown for a coax connection or a differential connection?

My system is used in a VERY noisy environment. I'm using coax based on a previous recommendation from this forum. I'm finding that I can improve noise immunity somewhat by having the firmware manually set the Eq gain to the lowest setting, i.e. 0x00. Does this make sense?

Thanks,

-Randy

over 11 years ago

0 Mark Sauerwald88474 over 11 years ago

TI__Genius 13475 points

Randy

The input equalizer on the DS90UB914 is intended to be operated in automatic equalization mode although as you note there is a manual mode. The amount of equation can be read in register 0x04, and the value will always be '0's for the MSB, transitioning to a '1' and all lower bits being '1' - i.e. 0000001 and 011111111 are valid results, but 01011111 is not.

00000000 is the lowest level of equalization, 11111111 is the greatest level of equalization. The actual gains are not guaranteed, but max equalization is approx 16dB at 700MHz, the equalization value can also be read from register 0x4E.

The gain is the same regardless of if the connection is single ended or differential, but with a single ended signal, the actual signal size is smaller.

In a noisy environment, your primary concern should be the signal to noise ratio, the optimum equalizer gain setting will depend upon the frequency characteristics of your noise. If you have a lot of noise in bands where there is not much signal strength, then increasing the equalization gain may well decrease the signal to noise ratio.

0 Randy Luck over 11 years ago in reply to Mark Sauerwald88474

Prodigy 240 points

Mark-

Further investigation shows that much of our noise seems to be between about 10 and 30 MHz.

We are using the '913A/'914A with data that has a pixel clock of 80 MHz. We are using them in the 10 bit mode.

From what I gather, the data path encoding is more than just a simple 1:10 serialization of 80 MHz times 10 bits to say 800 MHz (in my case). (Or 960 MHz if HSYNC and VSYNC are also included.) From reading other posts, I gather that the encoding and transmission method seems to be much more complicated with other frequency ranges in play.

If I could insert a -10dB filter between 10 MHz and say 30 MHz, that might solve my problem.

Thanks,

-Randy

0 Mark Sauerwald88474 over 11 years ago in reply to Randy Luck

TI__Genius 13475 points

Randy

If you are able to filter out the noise between 10 and 30MHz, that may do the trick. The 913/914 uses a band from ~70MHz to 700MHz for the forward channel, and a second band from about 1MHz to 5MHz for the control channel. Your noise seems to fit nicely between the two.

The data path encoding is more complicated than just a 1:10 serialization. We do an encoding which assures a minimum amount of DC content, as well as encoding other lower frequency signals (part of the control channel and HSYNC/VSYNC) along with the forward channel video data. The result is a forward bit rate which is 14X the PCLK rate (for your 80MHz PCLK, the forward data rate will be ~1.1Gbps - so the upper limit of the band that it uses will be ~600MHz, and the lower edge of that band is about an order of magnitude lower or about 60MHz

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DS90UB914 Eq settings