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Opamp to drive broadband transformer

Andrey Sachko
Prodigy 250 points
Other Parts Discussed in Thread: LMH6550, LMH6552, THS3120, THS3095

Hello

Can someone from TI people help me? I need to choose the right Opamp IC. I need to inject broadband PRBS signal via transformer on resistor 20-50 Ohm. I need to develop up to 0.5V magnitude of the signal on this resistor.

Lets assume, PRBS signal has bandwidth BW=200 kHz, or even less than this.

What fully differential opamp should I use? Or, I need to use two Current Feedback opamps ?

Please help

Andrey

  • 0
    TI__Genius 13935 points
    Hello Andrey,

    I would suggest the LMH6550 or LMH6552.

    Regards,
    Loren
  • 0 in reply to Loren Siebert 1
    Prodigy 250 points

    Hello, Loren

    Thank you for the reply. I have transformer with 1:1 turn ratio. And I see in LMH6550 datasheet that all measurements were done at RL=500 Ohm (diff load resistance). Will LMH6550 behave properly at RL=20 Ohm? How about linearity? Voltage swing is not big in my case. I think all these fully diff opamps were designed for ADCs, which are actually not low impedance loads.

    Most likely, I will use CFA opamp with bipolar power supply. Do you have the chip similar to LT1210 ?

    Hear from you

    Andrey

  • 0 in reply to Andrey Sachko
    TI__Genius 13935 points

    Hello Andrey,

    If you use a 4:1(turns) transformer then the load to the amp would be 20*16 = 320 Ohms and the votlage swing would be 0.5 * 4 = 2V.

    This is what transformers are designed for.

    For a 1:1 transformer I agree the amps I suggested are not the best.  You might look at the THS3120 or the THS3095. 

    For future reference we have an online tool for cross referencing parts:

    Regards,

    Loren