ONET1151L: Support Components

Michael Nycz

Part Number: ONET1151L

I am trying to use the ONET1151L in a new design. I have used this chip in the past and used the eval board schematic as a basis for my project's design. Using that schematic I have had no performance issues.

For the new design, I need to pack this laser driver into a very tight space. In the eval board schematic, there are a number of components on the outputs of the laser driver referred to as "bias tees". They are made up of a 475 Ohm resistor in parallel with a 47uH inductor, and this combination in series with a BLM15HG102SN1 ferrite bead. Given my space constraints, I was wondering if I could remove any of these components and have the ONET1151L still function and perform at 10G? Since they are "bias tees" I assume the 475 Ohm resistors need to be there. My question is, can either the 47uH inductor or the ferrite bead be removed or at least downsized to a smaller device? The other question is, if I remove them, what impact would there be on the output performance of the laser driver? Any help here will be greatly appreciated.

Thank you,

Mike Nycz

over 6 years ago

0 Nasser Mohammadi over 6 years ago

TI__Guru* 93670 points

Hi Mike,

Inductors provide some level of peaking on the output eye diagram optimizing eye diagram. Otherwise, we would have a double eye or high jitter at eye crossing. So the passive components on the output pins are indeed needed.

Regards,,nasser

0 Michael Nycz over 6 years ago in reply to Nasser Mohammadi

Intellectual 835 points

Nasser,
Thank you for the response. I suspected that the components were necessary. Can alternate components be used that are smaller in size? The 47uH inductor is a 0603 sized device. Could the current rating used be less to allow a smaller device? I am trying to make the circuit footprint as small as possible.

Thank you,
Mike Nycz

0 Nasser Mohammadi over 6 years ago in reply to Michael Nycz

TI__Guru* 93670 points

Hi Mike,

This circuit was recommended using 47uH 0603 inductors and using these components we know there is no double eye at the eye crossing. These inductors provide a DC path for current source. Also, di/dt creates overshoot to help with the eye crossing. Whether we can reduce DC current rating depends on your laser bias current. I think the lower bias current the more likely hood that we can reduce size of these inductors. However, it would be a good idea to get perhaps 10 boards and change to the newer inductor just to make sure AC and DC response meets your requirement. Additionally, it would be a good idea to create a simulation environment using present 0603 inductor model and then switch to the newer one just to make sure all look good.

Regards,,nasser

0 Michael Nycz over 6 years ago in reply to Nasser Mohammadi

Intellectual 835 points

Nasser,

Thank you for the information. The one thing that I have found is that the P/N that is specified on the eval board (TDK GLFR1608T470M-LR) is now an obsolete part. I have looked on Mouser and Digikey to find a part that has comparable ratings. The only ones that I found were huge. Can TI recommend a new inductor that would at least be in the 0603 size range?

Thank you,

Mike Nycz

0 Nasser Mohammadi over 6 years ago in reply to Michael Nycz

TI__Guru* 93670 points

Hi Mike,
I just checked DigiKey and this seems to be available and there are 13K pieces available. Please note link below:
www.digikey.com/.../1856578

Mouser says they are available as well:
www.mouser.com/.../GLFR1608T470M-LR

Regards,,nasser

0 Michael Nycz over 6 years ago in reply to Nasser Mohammadi

Intellectual 835 points

True, but it is the long term that I am worried about. Both places say the P/N is end of life and will be discontinued.

0 Nasser Mohammadi over 6 years ago in reply to Michael Nycz

TI__Guru* 93670 points

Hi Mike,

You can consider this part from KEMET:
www.digikey.com/.../8601362

Regards,,nasser

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ONET1151L: Support Components