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Low voltage virtual ground

Discussion in 'Electronic Design' started by garyr, May 2, 2013.

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  1. garyr

    garyr Guest

    I need a half-rail virtual ground in a 3.3 volt circuit. I couldn't find
    anything like a TLE2426 that would work at that voltage so I thought I would
    use a low-voltage opamp configured as a follower with VCC/2 connected
    to the positive input. The TI LMV721 has a supply voltage range of 2.2 to
    5.5 volts and a GBW of 10 MHz. That would be probably be acceptable
    but I would like to extend the range of low impedance output to as high a
    frequency as possible and so perhaps a cap on the output would be helpful.
    The data sheet implies that the '721 is stable with 2.1 nF on it's output
    with a 2.2 V supply and 21 nF at 5 volts, but doesn't state a maximum
    value of capacitive load. Linear extrapolation would imply that 9.5 nF
    would be OK at 3.3 volts. Any idea wha the actual maximum value
    might be?

    Also, my circuit will not impose a DC load on the virtual ground; should
    there some DC load on the opamp?
     
  2. Robert Baer

    Robert Baer Guest

    Well, i would put a resistor in series from opamp output to "load"
    /virtual ground and a capacitor from there to ground for the HF bypass
    needed.
     
  3. whit3rd

    whit3rd Guest

    or two resistors and two capacitors (if the power-on/off transient behavior matters).
     
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