• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 47 subscribers
  • Views 576 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.

How to reduse DC offset with noise

Sampath Bandara
Prodigy 180 points
Other Parts Discussed in Thread: THS4215, OPA695, OPA843, OPA846, OPA847, LMH6618

To whom it may concern

I am sampath bandara from university of Mississippi, atmospheric lighting research student. Currently I am working on atmospheric lighting electric field measurement and I construct circuit for my antenna it is working but problem is we got  300mV noise (DC offset with noise (figure 1,2) when we are connecting  circuit  to the computer daq input.

Important- circuit is not constructed on PCB I used manhattan method circuit construction and not proper power supply and initially does not use any high pass filter.

Now I wont to reduce this noise and Dc offset without lose any gain I highly appreciate if you can give me any suggestions regarding this matter.

Important- green color is the output signal

Thank you

Sampath Bandara 

  • 0
    TI__Genius 12631 points

    Hello Sampath,

      Have you tried probing the output of the THS4215 stage (with an oscilloscope) to observe the output. This would be a good 1st step to confirm that it is the THS4215 that is the problem. The offset voltage can be explained: the datasheet specs the Vos of the THS4215 as 12mV max. You also have the amplifier in a gain of 11, so the max output offset voltage of the 1st stage can be as high as +/-132mV. Also, the 56.2Ohm(R3) load at the output of the THS4215 is quite a heavy load. Can you please change that to 500Ohms and see if it improves? I am not sure why you have the intermediate noise - is there a stimulus happening somewhere else on the board at these points to cause the noise.

    I can help you select a part with lower Vos; can you please let me know your bandwidth requirements?

    Also, you could ac couple the output of the 1st stage to the 2nd stage. Is this an option?

    I should mention that high speed amplifiers tend to be very sensitive to any extra parasitics and could oscillate if careful layout techniques are not followed. You could purchase an EVM of the THS4215 from the link below to better debug your circuit, if necessary.

    http://www.ti.com/tool/ths4215evm

    Samir

  • 0
    Prodigy 180 points

    Thank you for the reply friend

    My first requirement is band width 1khz to 5Mhz (I know this op amp is too much band width but I tried several op amp but this one is the only one work for me-THS4215,THS4203,OPA695, OPA847ID OPA846,OPA847,OPA843)

    I do not know why it is, sometime my electronic knowledge is not enough.

    According to your suggestion you said that THS4215 output load is heavy (I used 56.2 ohm)

    You mean I have to try 500Ohms.

    I have another things can I remove this offset using 1Khz high pass filter

     

  • 0 in reply to Sampath Bandara
    TI__Genius 12631 points

    Hello Sampath,

    The 1KHz low pass filter is not going to help since the dc offset is at very very low frequencies. I suggest using a part like the LMH6618. The dc offset of this part is much lower, around 1mV. Also, the bandwidth of this part is sufficient for your requirements, 130MHz. Please let me know if this is a better option.

    Thanks,

    Samir

  • 0 in reply to Samir Cherian
    Prodigy 180 points

    Thank you for reply

    I think I need at least  100V/µs Slew Rate op amp   as our sampling rate

    I like to ac coupling for my previous circuit but we can not reduce dc offset ?