ONET8551T: DC Offset Cancellation

Would it be possible for TI to provide responses for these questions sometime soon?  I'm under some schedule pressure on this issue.  

Also, one additional question.

10. If the current into the "IN" pin is made to have zero average using external offset cancellation circuitry, will the IC's internal AGC and RSSI circuitry interpret this as meaning that there's very little current flowing from the detector, even if there's a large AC current going into the pin?  

I'm urgently in need of a response to this question and would be very grateful if a TI representative could respond soon.

Hello Richard,

I apologize for a delayed response; our ONET devices are complex and our subject matter experts are on business travel.

I am waiting to hear back from the team on the operation/functionality of the DC current cancellation circuitry.

In the interim, is your application one where ONET devices would be required?  We have an expanding portfolio of TIAs and even a new laser driver IC which are available (and newer) than our ONET developments.  This includes our LMH13000 laser driver IC, our OPA85x family of TIAs (including OPA855 and OPA858), and our LMH32401/LMH32404/LMH34400 integrated TIAs.

I mention our other portfolio devices as we do see customers intending to implement a system who default to considering ONET devices but for whom the aforementioned devices can be of use.

If your questions are better answered by using the device in-lab on a bench, you may also request a sample.

Please also share if your minimum required information has changed to retain consideration of our devices in your system.

Best,

Alec

Hello Alec,

Thanks very much for your helpful response!  For this application we need at least 5 and ideally 10 Gb/s, so the ONET information is still needed.  We'll be dealing with dark currents of up to 1 mA and additional small offsets from ambient light.  The main things I need to know are how much offset current can be compensated for by the IC and how fast the internal offset current cancellation control loop is.  If those numbers don't meet the needs of our application, I need to know whether externally cancelling all of the average photodiode current (with due care to avoid excessive capacitive loading on the sensitive input) will introduce side effects that prevent the AGC or other elements of the IC from functioning normally.

The LMH13000 is especially interesting for other important applications of my customer's unique lasers but for the current application, it would be very beneficial to have a device exactly like the LMH13000 but capable of 10 Gb/s modulation.  Is there anything like this currently available from TI or on the development radar?  The high bias current and high and easily controllable modulation current capability are key characteristics of value.

Also, the lidar oriented LMH32401 and LMH32404 TIAs you've suggested include ambient light cancellation that would be very beneficial to us if it was available with a TIA capable of 10 Gb/s performance.  Is anything like that available from TI or on the development radar?  If not and if the ONET TIAs prove unsuitable, we might also consider developing our own photodetector TIA circuit based on an IC similar to the OPA855 but capable of 7-8 GHz bandwidth when a 500 ohm or larger feedback resistor is used in the low noise transimpedance first stage. 

All that being said, at this point it looks like our best option is the ONET8551T if the necessary offset cancellation can be achieved with it. 

Best regards,
Richard

Hello Richard,

Glad to hear some of our portfolio has interest; I will check and see if we have roadmap plans inclusive to your considerations.  If we have an interested party internally, I can connect you with them once I learn more.

I am waiting to see if my colleagues can provide more information on the offset cancellation for ONET8551T.

Best,

Alec