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Opamp to work with ADS62P28

Andrei Hanu
Prodigy 20 points
Other Parts Discussed in Thread: ADS62P28, THS4503, THS4513, THS4511, THS4508, THS4509

Would somebody suggest an opamp to work with the ADS62P28 (12-Bit/210 MSPS)? All of the reference designs suggest the transformer approach, but I would like to use an opamp.

 

Some typical signal input would be.

Input Impedance: 50 ohm

Amplitude Range: +/- 3 Volts

Rise Time: 100 nsec

Decay Time: 140 usec

Signal Bandwidth: approx 100 MHz

 

I've been looking at the THS4513, but I'm not sure if its the right one to choose. Also have looked at the THS4503.

  • 0
    TI__Genius 17310 points

    Hi Andrei,

    It sounds like your best options are going to be either the THS4511 or the THS4513. The THS4511 allows for DC coupling to a signal with an input common mode voltage of 0V. If you are AC coupling then the THS4513 is a better option. The THS4508 or THS4509 could also work, but they are only stable down to a gain of 2 V/V.

    With such a large input signal it sounds like you may want to use the amp as an attenuator. Although the amp is only stable down to unity gain a resistor network can be used at the input to attenuate the signal before going through the amplifier. There is a series of application notes on the TI website about how to use fully differential amplifiers as attenuators. The link to the Analog Applications Journal is below where you can find the articles.

    http://focus.ti.com/general/docs/gencontent.tsp?contentId=29569

    Regards,
    Matt Guibord

  • 0 in reply to Matt Guibord
    Prodigy 20 points

    Hi Matt,

     

    Thank you kindly for your prompt and insightful answer to my question. Between the different op-amps price seems to be relatively the same so that's not an issue. Also, the pinout is the same so it seems I can safely interchange between different opamps to see how they perform. I plan on driving them with a single supply from 3.3 Volts which is readily available from the Spartan 6 power supply. This limits me to THS4509 and THS4513. 

    Based on your suggestion, I will use the THS4513 since it seems to work nicely in an AC coupled system. 

     

    Also, thank you for the link to the APP notes on running the opamps as attenuators. It was certainly most helpful with my calculations for the gain and feedback resistors.

     

    Cheers,

    Andrei