Simple biasing method?

Discussion in 'The Projects Forum' started by bennyb86, Mar 10, 2008.

  1. bennyb86

    Thread Starter New Member

    Mar 10, 2008
    1
    0
    Hi everyone,

    I am building a hardware DCC encoder and am stuck at what should be a fairly trivial point.

    I have a square wave pulse that goes from +5V to 0V. Basically I need this pulse to be symmetrical around 0V so I need it to go from +2.5V to -2.5V. ( I will then amplify this using an op amp).

    Could anyone please suggest how I could do this please?

    many thanks,

    B
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You can use a cap to block the DC, and a resistive divider to pull the average voltage level wherever you need it, or in this case, a single resistor to ground.

    The cap must be a low-ESR type. An electrolytic cap will not work well.

    The resistor should be fairly large, otherwise the circuit will begin to resemble a differentiator.

    See the attached schematics and simulated O-scope trace of inputs and outputs.
    Note that the only differences between the two is the value of R1 and the output signals.
    The larger the value of R1, the more symetrical the square wave will be, but the longer it will take for the waveform to be centered around 0v. However, if you are using an op amp in open loop mode, the symetry shouldn't be much of a concern.

    Level ShifterOpAmp shows the output of the level shifter amplified by a noninverting op amp in open loop mode.
     
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