Single-supply op amps

Discussion in 'General Electronics Chat' started by blah2222, Nov 27, 2013.

  1. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    Hi all,

    Silly thought that has been bugging me for the last while.

    I have an AD620 (instrumentation amplifier) that requires a split-supply. I am using a 9V battery and have created a virtual ground at the battery's mid-point (+4.5V) using a TLC277 (single-supply) op-amp to attach to the AD620's reference pin.

    My question is, if I pass the output of the AD620 through a passive high-pass filter and then through an inverting amplifier (using the TLC277) does the resistor in the high-pass filter need to be tied to the virtual ground (+4.5V) or can it be connected to the negative battery terminal and the same question regarding the positive input of the op-amp?

    From what I have understood, a single-supply op-amp is pretty much the same as a split-supply op-amp but it can be operated much closer to the supply rails for inputs and outputs.

    Would it be fair to say that "rail-to-rail" and "single-supply" are synonymous?

    Thank you,
    JP
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,001
    745
    Show us your circuit so we can assist you,

    split supply's using op amps must be low impedance ideally, using transistor buffers, or using a power op amp, the datasheet (pages 15/ 17) says to connect the Ref pin 5, to psu ground.
     
    Last edited: Nov 27, 2013
  3. LvW

    Active Member

    Jun 13, 2013
    674
    100
    No.
    There are neither split-supply nor single-supply opamps.
    Each opamp can be operated with single or double supply voltages.
    However, there are some opamps that have been OPTIMIZED for single supply operation (to come as close as possible to ground potential).
    And there are also some opamps (rail-to-rail) which are optimized to come as close as possible to both of the supply rails.
     
    absf likes this.
  4. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    This circuit isn't an inverting case but does the trick. This example assumes a split-supply.

    Supposing the image is of a single-supply op-amp, would this still work? I.e connecting R1 and R3 to GND rather than Vcc/2 to have an output that is biased around Vcc/2?
     
  5. LvW

    Active Member

    Jun 13, 2013
    674
    100
    Yes - connecting R1 and R3 to Vcc/2 would work as single supply biasing. However, other single supply configurations are also possible.
     
  6. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    I was asking if it would work in a single-supply condition (Vcc & GND) when both are connected to GND.
     
  7. LvW

    Active Member

    Jun 13, 2013
    674
    100
    I don`t understand. Is my answer not clear enough?
    I repeat: Connecting R1 and R3 to Vcc/2 would work as single supply biasing.

    How do you think could the dc output biased at Vcc/2 with R1 and R3 grounded?
     
  8. blah2222

    Thread Starter Well-Known Member

    May 3, 2010
    554
    33
    And again, I never asked about connecting R1 and R3 to Vcc/2. I know they work.

    I was asking about grounding R1 and R3 as I was wondering if some single-supply op-amps had internal circuitry that biased the output to Vcc/2, even though the reference is the same as the negative rail (GND).
     
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