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differential or single-ended???

Manuel Malagon
Prodigy 250 points

Other Parts Discussed in Thread: ADS8318, THS4521, ADS8323, AMC1200

Hi everybody

I have little experience in signal acquisition and now I´m facing a big problem, for some of you is something easy to understand so that´s why I need help.

I have to design a system that has to acquire a signal. This signal is about 200mv p-p and in a frequency range from about 1KHz to 20KHz. The place where I have to acquire this signal is very noisy and a little far away from the acquisition system and this signal has to "enter" in to my MCU as pure as it could be because I have to analyze it.

I need help to place in order my ideas and to find a good solution for this situation. I have a couple of questions.

  1. I´ve read that differential signals are better in terms of noise rejection and, should I use this kind of ADC (and ADC op amp driver)?
  2. If I use the "differential approach", I was thinking about putting my sensor, which is single-ended, and then convert the signal to differential with a THS4521. Then, transmit the signal over the long cable, recieve it with another THS4521 and finally fed it in to the ADS8318 ADC. Is this correct?
  3. Also, if I use the "differential approach", can I calculate the system using the app note SLOA054D?
  4. If the differential approach is not what I understand, Could you help me to find the correct information source to figure out a proper solution?

I hope anyone to help me, I´ll appreciate it very much because I´m stuck with this. Thank you very much

  • 0
    TI__Guru**** 182821 points

    Hi Manuel!

    Your 'new' to our side of the e2e community so "welcome aboard"!  Differential signaling certainly buys you noise immunity so your on the right track.  I see you've been active in the Stellaris and MSP430 forums.  What sort of resolution do you need from this sensor?  What sampling rate are you looking for?  The THS4521 would be a great option.

    Depending on your application, you also might consider using something like the AMC1200 which will give you a differential output that you may be able to drive directly into one of the MSP430 or Stellaris 'on-board' ADC's depending on you resolution needs.  If you're looking at an external A2D converter, the AMC1200 could also drive directly into something like the ADS8323.  Give us a little more detail if you can on the system requirements and we'll try to give you the best overall solution options that fit your ultimate needs.

  • 0 in reply to Tom Hendrick
    Prodigy 250 points

    Hi Tom Hendrick!!

     

    Thank you very much for your answer. The reason I have to use an external ADC is because I have to make a high-accuracy low-noise signal acquisition module for a FPGA. The system already has an FPGA so I can't use another controller, that's why I couldn't use a stellaris MCU.

    What the system must do is acquire a signal from 6 electret microphones in order to analyze it. Is an audible sound in the range from 1kHz to 20KHz but the microphone is placed about 1 meter from the system and in a very noisy environment. I need about 500Ksps or more to get this signals with high accuracy and avoid alias effect.

    So, can I do this arrangement? I mean, can I put a THS4521 very close to one mic, convert this signal to differential, put it in to the cable and transmit it one meter away up to the acquisition system, then receive the signal with another THS4521 and finally feed this signal in to my ADS8318?

    Also, thanks for the suggestion about the AMC1200 as I have another application which suits well for this isolated OpAmp.

  • 0 in reply to Manuel Malagon
    TI__Guru**** 182821 points

    Hi Manuel,

    This 'sounds' like an interesting project (forgive the pun!).  I talked with one of the application engineers for the THS4521 and he believes your approach would be fine.  His suggestion is to put 50 ohms (or so) in series with each output to isolate the amp from the cable parasitics and adjust gain resistors on the receiver side to get to the full scale range of the ADS8318 (+/-Vref, with min Vref of 2.048V).