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THS3091 implement issue on Arbitrary Waveform Generator output Drive Circuit

Alan Yeh
Prodigy 20 points

Other Parts Discussed in Thread: THS3091

My customer, they found THS3091 DS Page 1, there are Typical Arbitrary Waveform Generator output Drive Circuit.

They tried to implement the design on. But THD is not good enough to meet their product spec. I undertook the Technical Support Task.

I could not find application note for Arbitrary Waveform Generator output Drive Circuit.

Please help

Alan

  • 0
    TI__Genius 13935 points

    An ARB is generally a lot like a DAC as shown in the datasheet example. Is your circuit exactly like the datasheet example?  It is unlikely that a composite circuit like this would meet single device specifications from the datasheet.  Are you using the same DAC? 

     What frequency is the THD specification not meeting requirements? 

      Most ARBs have a 50 Ohm terminated output so this will require termination resistors which may require 6dB more gain.  The datasheet example is very generic. 

    It's possible you may need to move up to a higher performance amplifier.  Are there voltage supply or power constraints?  Is rail to rail necessary?  Can you go with a split supply amplifier that takes more power? 

  • 0
    TI__Expert 4115 points

    Alan,

    The THS3091 is probably the most capable Op Amp for high voltage swing into heavy load, but it does have its limitations. It is common for customers to try to push the performance beyond what the device can do. The concept  circuit shown with 3 op amps in parallel is capable to provide 20Vpp into a 100 ohm load, which is 10Vpp at 50 ohm load with 50 ohm series output (150 is series with each op amp) up to 20MHz. I think -40dBc THD is a realistic performance expectations in a production environment  under this condition.

    I don't know of any ARB specific app notes, but as Loren mentions in another post, a big part of the design is the DAC interface. There are some app notes on TI.com for that; here are 3 for various types of DACs.

    Interfacing op amps to high-speed DACs, Part 1: Current-sinking DACs http://www.ti.com/lit/an/slyt342/slyt342.pdf

    Interfacing op amps to high-speed DACs, Part 2: Current-sourcing DACs http://www.ti.com/lit/an/slyt360/slyt360.pdf

    Interfacing op amps to high-speed DACs, Part 3: Current-sourcing DACs simplified http://www.ti.com/lit/an/slyt368/slyt368.pdf

  • 0 in reply to Jim Karki
    Prodigy 20 points

    Dear Jim

    Thank for your comment for this issue. It have been happen for a year. We found THS3091 is hardly to be used on their system specification -30dBc @ Vo=20Vpp 60MHz.

    About THS3091's Performance Shift on process variation (TI Declared those "Performance Shift Devices" is valid on 2011/9/08), Customer felt angry and hopeless without other alternative solution and devices.

    So Customer sort and pick up TH3091s with better THD, by themselves.

     

    Anyway, Thank you again.  I will try to approach their new development plan.