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OPA2683: Sel

Nishant Gupta
Intellectual 390 points

Part Number: OPA2683
Other Parts Discussed in Thread: THS4551, OPA2836, OPA836

Hello TI Team,

I am looking for a high-speed, unity-gain-stable amplifier to use as a buffer stage immediately before the input of my THS4551 fully differential amplifier (FDA).

My application requirements are:

  • Signal: single ended Pulse waveform, approximately 0–2.8 V steps waveforms any voltage in between .

  • Frequency: 7.5–10 MHz.

  • Rising slew rate: 80 V/µs.

  • Falling slew rate: 45 V/µs.

  • Configuration: Unity-gain voltage follower.

  • Priority: High bandwidth, fast settling time, low distortion and stable operation when driving the THS4551 input.

  • Purpose: Accurate characterisation of a high-speed 14 bit ADC.

Could you please recommend a suitable TI amplifier and clarify the following?

  1. What minimum gain-bandwidth product, slew rate and settling time should I target?

  2. How can I verify that the buffer settles adequately before the THS4551 input under my pulse conditions?

  3. What output-drive capability and capacitive-load stability considerations should I account for?

  4. Would a wideband voltage-feedback amplifier or another amplifier topology be more suitable for this application?

  5. Are there any recommended reference circuits or evaluation modules for this configuration?

I would appreciate a suitable part number and guidance on the calculations required to verify the amplifier's performance.

Thank you for your support.

Best regards

  • 0
    TI__Prodigy 340 points

    Hi Nishant, 

    I would recommend using the dual channel OPA2836 to use as a buffer stage before the THS4551.

    1) The minimum gain-bandwidth product, slew rate, and settling time should meet the minimum requirements for the THS4551. So in this case, according to the datasheet for the THS4551, I would suggest a minimum gain-bandwidth product of 150MHz and a slew rate of at least 220V/us. Essentially, you don't want your buffer to be limiting your FDA.  

    2) This depends on what you choose your settling time to be in your design. Please obtain your ADC's acquisition time and sample-and-hold capacitance, then use this Analog Engineer's Calculator (https://www.ti.com/tool/ANALOG-ENGINEER-CALC) to size the RC charge-bucket network and verify settling within the sampling window. 

    3) Can you clarify if you are asking about the output-drive capability and capacitive-load stability in regards to the buffer/FDA or in regards to the FDA/ADC? It depends on your configuration. If your question is for drive capability and loading from the buffer to the inputs of the FDA, this wouldn't be a necessary concern since you are driving just the Rg of the FDA rather than loading something. 

    4) Yes, a wideband VF amplifier would be more suitable for this application rather than a CF amplifier since your application requires a unit gain voltage buffer. 

    5) Please look at page 33 of the OPA836 (https://www.ti.com/lit/ds/symlink/opa836.pdf). It provides a good reference circuit for your application. The recommended EVMs will also  depend on the package you decide to use. 

    Best,

    Amber Lee