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Single ended signal over TL072 to a differential line

Discussion in 'Electronic Design' started by Rüdiger Leibrandt, Apr 18, 2007.

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  1. BUT HOW?!

    I find hundred of publications online taking care of the conversion from
    differential to single ended signals , like id=100&
    but I need it the other way round - I need to drive a weak signal over a
    highly exposed area to my measuring-station.

    Anyone knowing where I may find something that tells me how I get the
    starting side of the sensorline working?

    All hints and help appreciated!
  2. You dont say how large the signal is, or the bandwidth, or cable type

    Assuming twisted pair cable, and say 20K B/W you could start by
    having a pseudo differential signal. Connect the output of your 072 to
    one of the lines via a 50 ohm resistor, connect the other cable to
    ground with another 50 ohm resistor, this will look like a balanced
    signal to a differential receiver and have good common mode rejection,
    maybe about 6dB worse than a fully balanced output

  3. Ai - sorry!
    input signal is "a few" millivolt ( usually - I will need to have potis to
    fine-tune the amplification I think ) but can go up to as much as 5 Volts
    in the seldom extreme. The lines are an ethernet Category 5 cable, 8
    meters, running straight into a ( not defined ) differential input of a
    PCI-datasampling-card in a PC. The sensor is a small K-Band transceiver (
    aka radar ;) from InnoSent ).
    I do not know where to add the resistors to shape and tune the output of the
    combined opamps. I'm lost if and where to add the poti's to control the
    amplification and so on. I hope that there might be a website with an
    example circuit which I could adapt to my needs.
    will show you the basics

  5. Winfield

    Winfield Guest

  6. Yeah, I know, but he did say single ended, I had thought of mentioning
    diff drivers etc. But there is too much "Nah you dont want to do it
    that way" around here, when a 072 will do the job.

    Anyway, lets see how the OP gets on.

  7. Winfield

    Winfield Guest

    You'll need feedback components for the two driver ICs, and don't
    the cable-matching resistors Martin pointed out. The receiver end
    input-protection stuff, and a real diif amp, see Martin's part
    selection -
    you likely don't want a power opamp for a receiver!
  8. have a look at TI's DRV134 data sheet.

  9. The single opamp on the right I added just to get the concept clear - the
    PCI-Card has variable impedance differential inputs, the software can set a
    whole range of details like input capacitance, input impedance and so on. I
    just have my headaches with the part on the K-Band transceiver's side, how
    to get the input-levels configured correctly - I never before worked with
    differential line drivers other then resoldering ethernet-sockets.
  10. On Wed, 18 Apr 2007 12:42:52 +0200, in Rüdiger
    Cut off the connectors and use a terminal strip. It has the added
    advantage that nobody will steal the cable for expanding the network

  11. Eeyore

    Eeyore Guest

    Also see my response in another group. It's similar but uses the TL072.

  12. Okay - the last word after a lot of datasheet reading is now a MAX435 - it's
    a wideband Transconductance Amplifier.
    I just need to find out how to give it a variable gain without ruining the
    impedance of it's output, and then I am fine.

    Thank you all very much for the help you provided to me!
  13. john jardine

    john jardine Guest

    Well a postscript then ;)
    Looks like the Maxim thing is obsolete.
    You'd have been better off with an AD8132.
  14. We have 30 of those Maxim IC's laying idly around - someday we would have
    thrown them away otherwise.... Thats active trash-reduction ;)
  15. joseph2k

    joseph2k Guest

    Having read this thread so far, it sounds like going for 4 to 20 mA SCADA
    transmitter is the way to go.
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