Looking for a LVDS buffer with Output common mode voltage of 0mv to 300mv (user Defined). Most LVDS buffers have 1.2V VCM Out. Is there a way to create such a buffer using amplifier circuit and be able to simulate the behavior. Vout pk-pk is required to be 200 mV. Any feedback will be helpful.
The 1.2-V common mode voltage is part of the LVDS specification, so you aren't likely to find any LVDS devices with such a low common mode. The simplest solution in my opinion is to just use series capacitors to AC-couple the buffer's differential output and then set the common mode to the desired level by using bias resistors at the receiver. I have attached a TI application note that goes into more detail on how to AC-couple different types of differential buffers to one another. In particular, you may want to take a look at Figures 9 though 11, which show three different methods of setting a receive-side common mode.
Please let me know if you have any questions.
Best regards,Max RobertsonAnalog Applications EngineerTexas Instrumentsmfirstname.lastname@example.org
First Thanks for your kind response. Problem is that I must DC Couple in order to carry Link Start DC conditions used by the Receiver. This is a Special receiver which looks for such conditions at 200mV. I was planning on using National/TI's ADC Differential Driver Buffers which allow VOCM to be adjustable to a defined Reference. I am not sure whether they will do the job or not? Any ideas using analog devices will be helpful.
I understand - if your system needs to be able to support DC levels then AC-coupling is not a viable option. Your idea of using an amplifier circuit sounds good to me. TI has several fully differential amplifiers that allow for the output common mode to be set using a CM bias voltage input. I recommend contacting our high speed amplifiers team to see if they can provide some suggestions. Here is their support forum:
One thing to consider when picking out a device is the bandwidth that is needed. If you are trying to preserve the rise/fall times of your input signal, a rule of thumb for the minimum bandwidth is 0.35 divided by the 10%-to-90% transition time. You should also make sure that the amplifier's slew rate is fast enough to handle the data transitions.
Best regards,Max Robertson
Thanks Max, I have posted it there now. Thanks for your feedback.
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