• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 46 subscribers
  • Views 2977 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.

Op Amp Recommendation

James Huang68835
Prodigy 30 points
Other Parts Discussed in Thread: LM318, TINA-TI

Normal 0 0 2 false false false MicrosoftInternetExplorer4

 

Hi, I am looking for an Op Amp to precisely follow up the input signal. The Op Amp is apply as an inverter and the input voltage is around 20mV~100mV with 300kHz frequency. The gain will be set to 100 when using 9V~12V single supply voltage and anticipate the output to be precisely without any delay. In my hand, I am now using LM318P which is an high speed Op Amp, but the output signal would distort when apply at such setting. Can anyone suggest any Op Amp with low quiescent current which price is below 1.00 | 1ku. Thanks.

  • 0
    Guru 21975 points

    James,

    It is not entirely clear what type of signals you are attempting to amplify and what type of distortion you are seeing with the LM318. Your input signal magnitude and gain (-100) suggests that you may be attempting to output undistorted 300kHz signal with 10 peak-to-peak amplitude. Passing reasonably undistorted sine waves would require an op amp Gain-Bandwidth of more than 30MHz and slew rate of greater than 10V/us. The LM318 falls short on Gain-Bandwidth. If you are attempting to amplify square waves or fast rising or falling edges without affecting the waveform, much greater GBW and SR would be required.

    Without more information on your signals or type of "distortion" it is difficult to make recommendations. If you provide more detail on the application we may be able to make a better selection.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 30 points

    Hi Bruce,

     

    Thanks for your reply. Currently I am using a waveform generator to generate a square signal in order to simulate the input source (from the touch screen surface).  However, the LM318 seems can't follow up at this speed. Below I have attached two pictures showing to have a -100 gain. The first image is having the input signal set to 10mV with 100kHz frequency, but the output is distorted. When I change the frequency to 300kHz, the output would come up like a sine wave. The second image is when the input is set to 100mV with 300kHz frequency, the result looks near a square wave but has been delayed. Could you recommend any Op Amp that will come out with a nice waveform with these settings.

    Thanks.

     

     

  • 0 in reply to James Huang68835
    Guru 21975 points

    James,

    It requires very high Gain-Bandwidth Product and slew rate to pass amplify square waves with good fidelity. I have simulated the circuit below with an idealized op amp model of 50V/us slew rate and 200MHz GBP. The slope of the output waveform early in the transition is determined by the slew rate. The curvature at the end of the transition is determined by the GBP.

    The GBP problem could be mitigated by breaking your gain into two gain of 10 op amp blocks (one gain of +10, the other -10). A similar waveform could then be produced with two op amps of 20MHz GBP.

    The need for high slew rate could be mitigated by reducing the output amplitude of the waveform. Combining the two mitigating factors could allow an op amp of much more modest performance to produce good square waves. You may want to try these ideas using our free circuit simulation program, TINA-TI. While there would be an investment in time to learn to use it effectively, you would find it easier to optimize this type of circuit.

    Alternatively, you may want to restate your question (summarizing the information you have provided here) on the high speed op amp forum. They may have op amps that better suit your application.

    Regards, Bruce

  • 0 in reply to Bruce Trump
    Prodigy 30 points

    Hi Bruce,

    Thanks for your help. Now I have a clearer direction to work on.