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THS4520: Single-ended to differential converter

Part Number: THS4520
Other Parts Discussed in Thread: LMH6612, LMH6629, , THS4521, THS4541, OPA838

Hi folks,

I’m looking for single-ended to differential converter with following minimum requirements but having some trouble looking for a good economical TI part:

3.3V single supply, 40MHz -3dB bandwidth, 2V peak-to-peak differential output on 100 ohms load, Gain of either +1 or +2 V/V, need rail-to-rail output since output might go up to 2.8V in a lower bandwidth configuration, 400V/us Slew rate, ac-coupled inputs and outputs.

I got the list of parts from TI portal using the filters.

Using 2 single-ended output opamps is a lower cost solution than using an opamp with differential output. I understand PCB layout of differential outputs becomes difficult with 2 opamps at this frequency. Can PCB parasitics cause potential EMI issues using 2 opamps at 40MHz speed?

If I use opamps with single-ended output, in a configuration as shown in Figure 66 of LMH6629 datasheet, using say LMH6612 which meets above requirements, the differential outputs are not symmetrical even after external compensation.

1)     Is 40MHz too high a bandwidth that it demands a true differential output opamp?

2)     Is it the topology that is causing asymmetry? Is there a different topology using 2 single-ended output opamps that might give differential output?

On the other hand, if I use differential output opamp, THS4521, seems to work fine up until say 5 MHz but at 40MHz, it clearly has issues though the datasheet implies it should work fine at this bandwidth. Also, I saw comments in the forum that its TINA model has lots of noise and performance issues and is an old product. Next option is THS4520 which seems to work fine except for peaking at around 250MHz. It also seems to be a little older product which is fine.

So, is my best option THS4520? Is there a more economical solution using 2 single-ended opamps?

Appreciate your thoughts or help.

Satish