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Differences between dual and single supply amps

Karen
Intellectual 940 points
Other Parts Discussed in Thread: THS4511, THS4513

What are the differences between single supply and dual supply amps. What is the major physical difference between them?

  • 0
    TI__Intellectual 940 points

    We spec and test some of our devices with split, balanced supplies because it places the mid-rail point at ground, which makes it easier to DC-couple inputs and outputs for testing. In actual operation, the devices that are specified with split supply operation can also be run at the corresponding single-ended supplies.

     

    So {+2.5V,-2.5V} => {+5V,0V} and {+1.5V,-1.5V} => {+3V,0V}.

     

    The only caveat is that you have to shift the inputs and outputs to the new mid-rail value if you want to preserve the maximum input and output swing and minimize distortion. Take for instance the THS4511 and THS4513; the datasheets show ways to shift the input common-mode voltages up or down. Basically it takes a couple of extra resistors on the input that are tied to the supply (up) or negative supply or ground (down). Some design equations are also included to help pick the resistor values. So for the TSH4513, the data sheet gives the input common-mode range as +/-1.4 with a {+2.5V,-2.5V} supply. If you shift the supply up by +2.5V to {+5V,0V} the input common-mode range will become +3.9V,+1.1V. Looking at the THS4511, it is very similar to the THS4513 except that it has been optimized to work in single-supply systems. The major difference between the two devices is that the input of the THS4511 has some additional level shifters that allow the input to go below ground, which can be convenient for +5V operation with DC-coupled inputs. I hope this information helps clarify the differences.