LMH6555EVAL: LMH6555

Hi Reza,

I will look through the our archived files for the original gerbers and get back to you.

Regards,

Hi Jacob,

Thanks a lot for the Gerber files

One quick question and wondering if you can help.

When using LMH6555 (or a similar DIFF_DIFF op-amp) to amplify a narrow pulse (i.e. 3ns wide pulse with high slew rate) then how wide the DIFF-DIFF should be to take advantage of DIFF-DIFF roll off as well?

How does the math work here? (DIFF2DIFF >> FIL >> ADC)?

If I keep the DIFF-DIFF wide then I may need to add filtering between DIFF-2-DIFF and ADC which doesn't look good. Although I understand the input to ADC at this ADC input should be clean enough to not need any such filtering.

Thanks,

-Reza

Hi Reza,

Can you clarify what you mean by how "wide" the diff-diff signal should be? Do you mean how much output voltage you should have?

Typically you want the output to deliver a full-scale signal into the ADC inputs based on the specification of the ADC. You may need to account for any losses from filtering between the amplifier and ADC inputs. I would suggest you at least add a small anti-aliasing filter between the amplifier and the ADC to eliminate any aliasing products.

Regards,

HI Jacob,

What I meant by wide was the band width of the DIFF-2-DIFF amplifier.

When amplifying a narrow pulse (i.e. 3ns wide pulse with high slew rate) then how would be the selection of the right op amp to make sure pulse is passing through and not degraded when it comes to slew rate and etc. and at the same time take some advantage of the op amp roll off. So say not just to go with very wide band width op amp? How does the math work here in relation with op amp specs?

Thanks,
-Reza

Hi Reza,

Apologies for the late reply on this thread. In general you can use a rough rule of thumb of amplifier bandwidth that is 3 x (1/pulse width), which would be 3.3 GHz for your pulse. This is just a rough rule of thumb so you could use the LMH6555 and you will get some roll-off because of the amplifier. You could also use the LMH5401 if you want a higher bandwidth device.

Regards,