DS15BA101/DS15EA101 can work at 50Mbps?

Hi Yang,

It is reasonable that the device can work at 48 Mbps. With that having been said, at 48 Mbps, there may not be much EQ provided by the equalizer. This is because an adaptive equalizer designed and ensured to operate in the 150 Mbps to 1.5 Gbps range has optimal boost capability within this data rate range. Below 150 Mbps, the boost provided is minimal or parasitic.

To explain this further, refer to a typical EQ transfer function for the DS38EP100  boost curve below:

The DS38EP100 performance is ensured for use from 1 to 5 Gbps. Outside of this range, the EQ is not optimized. Similarly, the automatic equalization from the DS15EA101 is not optimized outside of its ensured data rate range from 150 Mbps to 1.5 Gbps.

Thanks,

Michael

Hi Yang,

After some further investigation of this question, I feel the need to clarify my previous post.

Although it is technically feasible that the DS15BA101 and DS15EA101 can pass signal at 48 Mbps, the complete device performance is only ensured when you operate within the 0.15-1.5 Gbps range. This is due to the margin that can be ensured during production. If you choose to operate at a frequency lower than the design operating range of 0.15-1.5 Gbps, it may be difficult to select the AC coupling caps (larger caps are required to pass lower frequency signaling before the caps saturate). Also, LOS (Loss of Signal) detection may not function properly when the device is operating outside of the frequency range of the DS15EA101.

In summary, you may see noticeable variation in the DS15EA101 performance at data rates beyond the recommended range. Therefore, I highly recommend you consider another equalizer more suitable for 48 Mbps if you are intending to operate primarily in that range.

Thanks,

Michael

Hi, Michael

I am puzzled with how buffer/equalizer works. Is equalizer a high pass filter or somewhat like an amplifier. How do we get 0.15-1.5Gbps frequency range? Is that -3dB frequency? Or could you give me some reference(e.g. some website or electronic document describing how equalizer works) ?

Thank you

Yang

Hi Yang,

The equalizer works like a high-pass filter. There are different types of equalizers available (passive, active, fixed, variable). The difference is whether the equalizer attenuates low frequencies (passive) or whether it boosts high frequencies (active). More information about the use of equalizers can be referenced in p. 66-67 of the LVDS Owner's Manual.

The reason for the 0.15-1.5 Gbps frequency range is not a limitation to the EQ functionality. Instead, it is an operating input data rate requirement for TI to ensure that other auxiliary functions (for example, LOS detection) of the DS15EA101 IC work properly.

Thanks,

Michael

Hi, Michael

Thanks for the guidance. I have a general idea about how equalizer works now. I have done lots of tests about my design these days. The following figure is the detailed schematic about my serdes plus equalizer design. The serializer works at 16MHz, that means the line rate is 192Mbps(16x12).  8B10B is used for encoding and decoding. The original 8bit symbol is counter code.(1,2,3,4,5,.....)When I am using a short cable(less than 1 meter), the system is all OK.(Keep on running 24 hours without an error bit) But when I am trying to use a 100m CAT5E cable( TE connectivity, 6-219586-4), there are always some bit error, sometimes the bit error rate can exceed 1E-9. And this cause the deserializer  unlock. Is there any suggestion for this issue?

According to the document you provided I found that DS15EA101 is an automatic adaptive equalizer. And it said that the equalizer need some intimate knowledge of cable type, data rate and data pattern. So what is the requirement for DS15EA101? Why does datasheet not tell us about this?

BTW: Is there any scenario TI's customer successfully using of this chip?

Thanks

Yang

Hi Yang,

When there is longer cable, there is invevitably more loss to overcome. Cables have a typical amount of loss in dB per unit frequency, and the longer the cable, the steeper the loss. A CAT5E cable is typically quite lossy, and the more loss the system experiences, the more jitter results. This is most commonly seen as intersymbol interference (ISI) or duty cycle distortion (DCD). The more jitter on the line, the more likely it is that there are errors to the point that the deserializer can no longer achieve lock. It is expected that, once you exceed a certain length of cable, the deserializer will no longer be able to achieve lock due to loss being too great to overcome.

The adaptive cable equalizer implements various filters to determine the transfer function for the cable v. frequency. By determining this curve, the adaptive cable equalizer then makes an assumption about the amount of EQ needed in order to "reverse" the loss characteristic of the cable over frequency as closely as possible. There are several examples of the DS15EA101 datasheet for various cables used and the maximum data rate that can be achieved per unit cable length. The equalizer does not necessarily need to have an "intimate" knowledge of the cable type, data rate, or data pattern, as it automatically adapts to whatever you give it. However, as you have already observed, there is a limit to how much the DS15EA101 can equalize for any given cable, and it is up to the designer to determine what is acceptable.

The DS15BA101/DS15EA101 chips can be used for various designs, and we even have reference documents that detail how they can be integrated with other SerDes products to extend cable reach even further (Please see the Application Notes in the Technical Documents tab of the product folder). For NDA reasons, we cannot disclose information about specific customers.

Thanks,

Michael