• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 50 subscribers
  • Views 314 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Need Help for choosing the right amplifier

Felicia Uhl
Prodigy 50 points
Other Parts Discussed in Thread: OPA695, OPA684, OPA4872, THS3092, THS3091, THS3201, THS3202, OPA694, OPA691

Hi,

I'm a total newbie to choosing amplifiers and i need an operational amplifier to amplify a sine signal from 1Vpp to 10 Vpp (Gain=10) at a frequency of 50 MHz (maybe even upt to 200 MHz is this possible?), so which device would be the right one for me? or do i have to use multiple amplifying stages? And is is possible, in general, to get an op-amp with more than 1 in- / output?

Many thanks in regard

  • 0
    TI__Expert 4950 points

    Hi Felicia,

    So for 10Vpp with an operational amplifier, you will be using dual ±5V supplies.  The high gain, high BW combination is guiding you to current feedback architecture.  For the 50MHz BW requirement, you can get away with a low power device, the OPA684 and achieve 120MHz BW.  Higher bandiwdth (200MHz), will require a device with higher quiescent current such as the OPA695 which will support 350MHz at a gain of 16V/V.

    Multiple +In can be found in multiplexers such as the OPA4872 (4:1 MUX).

    To have multiple -In and Output, you can connect the +In of several operational amplifer together.  If good isolation between the multiple gain is needed, a MUX is normally the solution.  The figure on the fropnt page of the OPA4872 is a good place to start.

     

  • 0
    TI__Expert 3030 points

    Felicia,

    The minimum slewrate = 2Pi Vpk, so for 10Vpp @ 50MHz, this is 1570V/us and for 200MHz this is 6280V/us. A few other questions:

    a) What power supplies are available? To support 10Vpp single-ended output, you will need at a minimum of +/-6V (12V single supply), with potentially all the way up to +/-7.5V, or +/-12V, or possibly +/-15V.

    b) Are there other critical specifications needed? This usually includes distortion and/or noise but there are others.

    c) What is your load impedance?

    d) It seems that you need single-ended, but do you need differential outputs?

    For what is known now, there are a few options to consider. If you want to do it in one stage then here are some options...

    1) THS3091/THS3092: Current feedback amplifiers with high current drive. In a gain of 10, it can support a 180MHz bandwidth. But it does require +/-15V supplies. These are able to drive over 200mA of current.

    2) THS3201/THS3202: Current feedback amplifiers. To support 10Vpp, you will need to have power supply of +/-7.5V (or 15V single supply) or even +/-8V. But, it is much faster than the THS3091/92 part with 520MHz bandwidth in Gain = 10V/V.

    You could also split the gain into 2 stages if desired. The potential advantage is that you may be able to use an output amp in a gain of say 2 (which keeps the bandwidth higher) and the "pre-amp" in a gain of say 5. Under this situation, the preamp may be able to run on a +/-5V supply and the output is only 5Vpp with half the slewrate and lighter loading. There can be many amplifiers for this preamp including parts like OPA695, OPA694, OPA684, and OPA691.

    Last thing to consider is the power dissipation. If the desire is to drive many loads with the same amplifier, then the power dissipation will increase. Be sure to evaluate the RMS currents and voltages, power supplies, and package choices (Theta-JA).

    Cheers,

    Randy

  • 0 in reply to Randy S
    Prodigy 50 points

    hey randy,

    thanks for the fast reply.

    a) until now it's not clear which power supplies are available

    b)I dont know exactly but the amplified sine signal should be precise so i think it would be good to have low noise and low distortion

    c) i dont know.. sorry im a total noob

    d) I want to have single ended in- and output.

    I'm sorry that i'm not more precise...

    cheers,

    felicia