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THS4140: Will I get Sin Wave Output if my Input is DC voltage?

Pang
Expert 2415 points
Part Number: THS4140
Other Parts Discussed in Thread: THS4551

Hi Ti,

Currently we are looking at the THS4140 and just wanted to confirm that if we provide clean DC input of 5V to pin 1 and pin 8 will I obtain sin wave output or a straight line wave form? Appreciate for your feedback.

  • 0
    TI__Expert 8640 points

    Hi, 

    Under normal configurations, the THS4140 should output a DC signal if you apply only DC voltages to the inputs.

    Regards, 

  • 0 in reply to Jacob Freet
    Expert 2415 points

    Hi Jacob,

    What is the condition that if I provide an input DC signal but I've got the output as sin wave?

  • 0 in reply to Pang
    Guru 48395 points

    Well perhaps that could be an oscillation?? 

    Full circuit would be useful to pursue further. By that I mean a picture (schematic) is worth a 1000 words. 

  • 0 in reply to Michael Steffes
    Expert 2415 points

    Hi Michael,

    Please find below attached schematic and need your help to advise in what condition that we will get the output waveform as sin wave when providing the DC input +/-10V.

    Expected output: For current schematic, we expect +/-1.5V output from +/-10V input. 

  • 0 in reply to Pang
    Guru 48395 points

    You are showing the FDA with +/-3.3V supplies, seems kind of low for that part. I think you also want to tie the PD pin to the V+ supply and not float it - it does say it has a pullup, so maybe it is fine. 

    I would increase R99 and R109 to 50ohm each and see if the oscillation goes away. 

    Also, you are running an attenuator which is a noise gain of 1.15 here - a lot of these FDA's are compensated for min NG of 2 (gain of 1). NOt sure about the THS4140 itself (or how good its TINA model is), but you might run through the "Designing Attenuators" section in the THS4551 data sheet. I did run a quick sim, and the THS4140 looks fine as an attenuator with no added effort, try putting R99 and R109 at 50ohm, you do not show what the ADC load looks like, but certainly capacitive.