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Level shifting

Discussion in 'Electronic Design' started by Henry, Oct 13, 2003.

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  1. Henry

    Henry Guest

    Do anyone know the simplest way to convert range (-1.6V to 3.4V) to
    the range 0-3.3V by using Op-Amp?
     
  2. just to try the new PyAscii just posted, running on a unix box, it works!
    Thanks Gary Richardson.

    Vcc
    |
    \
    /
    \
    |
    |
    | + |\
    Vin ----/\/\-----------| \
    | >-----|------- Vout
    |------| / |
    | - |/ |
    | |
    | |
    | |
    -------/\/\-----|
    |
    |
    \
    /
    \
    |
    Gnd
     
  3. Why use an opamp? You don't need any gain, so a simple passive summing
    network will do fine. Assuming zero source impedance and infinite load
    impedance, this should work:

    ___ ___
    IN --|___|-o-|___|-- +3.106V
    |
    1.7k | 3.3k
    |
    |
    OUT

    The 1.7k and 3.3k resistors achieve the scaling from 5V to 3.3V range. The
    3.106V value comes from fixing Vi at -1.6V, Vo at 0V, and solving for the
    current through the two resistors, Vi / 1.7k = - Vx / 3.3k.

    Of course, if you don't have a handy 3.106V supply around, you could be a
    little more clever - note that the parallel combination of the 15.94k
    resistor and the 4.16k resistor is still equal to 3.3k:

    ___ ___
    IN --|___|-o-|___|-- +15V
    | 15.94k
    1.7k |
    | ___
    o-|___|-- GND
    | 4.16k
    |
    OUT

    And if you have nonzero input impedance, you could correct for it by
    changing the input resistor, or just by scaling all the resistors to be in
    some reasonable range.

    -walter
     
  4. gwhite

    gwhite Guest


    yes.
     
  5. JeffM

    JeffM Guest

    Did you mean convert range (-1.6V to 3.4V) to
    the range 0 to +3.3V by using Op-Amp?
     
  6. This is a good cheap solution if you know the impedance of the source and
    load. Using a pot this way can also work. However, if you want the circuit
    to be relatively independent of the impedance of source and load, an opamp
    is the way to go...

    Take a look at
    http://home.comcast.net/~rcmonsen/levelchange/levelchange.html for a way to
    do this with an opamp, which gives large impedance on input, and small
    impedance on output.

    Regards,
    Bob Monsen
     
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