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  • TI Thinks Resolved

The op amp selection

Genius 12080 points

Replies: 6

Views: 689

Hi team,

The customer would like to select an op amp and need us to provide an available circuit.

His requirements are as below:

1. The input signal is the 1mV amplitude wiht 2MHZ sine.

2. He would like to use single power supply.

3. He need to amplify 2000~3000 times.

4. The output voltage should be 0~3.3V. The output signal is used as the input signal of ADC.

I think this should use the double power supply. 

Would you help me to select a suitable op amp and send me a TINA circuit?

The attach is a TINA circuit for this application. Can anyone check it?High gain.TSC

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

  • Micky,

    Is the input always about 2MHz ? Relatively narrow band pass will be needed especially on the first gain stage(s) to keep noise level down.
    For the ADC input, does it matter if the value is peak, average, or rms value (of the input sine)?

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Hi Ron,

    Yes, the input signal is always 2MHZ. 1mV is the peak-to-peak voltage.

    Would you send me a available TINA circuit?
  • In reply to Mickey Zhang:

    Hi Mickey,

    It is going to be very challenging to achieve that much gain with a single amplifier design. Would the customer be willing to use a 2-stage amplifier design?

    Regards,

    Jacob Freet 
    High Speed Amplifiers

  • Hi Mickey,

    it's very difficut to achieve high gain with single power supply because when doing the biasing lots of the supply noise is injected into the signal path. So, lots of filtering is needed to keep the bias free from noise. In the following I have drawn a schematic with four OPA300. Three OPA300 provide a gain of 10, one OPA300 will give a gain of 2. More gain per single OPAmp stage isn't possible with the OPA300 because loop gain would drop too much and distortion would become too high:

    A double power supply would render all this bias filtering unnecessary!

    The first gain stage is non-inverting. This allows a low noise feedback loop with small R2 (100R) and a rather high input impedance of 1k at the same time. The overall distortion is only 0.35%.

    Kai

  • In reply to Jacob%20Freet:

    Hi Jacob,

    Thanks for your reply. The customer only needs to achieve his requirements and he does not request to use

    a single op amp or two or three op amps.
  • In reply to Mickey Zhang:

    Hi Mickey,

    Apologies for the delay. As Kai mentioned above split supply does have some benefits but it is possible to use a single supply if needed. Is the customer able to use a 5V supply or do they need an amplifier at 3.3V? We can look at the LMH6624 on a 5V supply or the OPA838 on a 3.3V supply and should be able to achieve the performance in two stages. I would suggest they set their output voltage slightly less than the target of 3.3V if they are on a 3.3V supply to add some room for offset errors.

    Regards,

    Jacob Freet 
    High Speed Amplifiers

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