# OpAmp I/O range determination from a datasheet

I found a similar question here and understood the following: input signal must be within the input common-mode voltage range of the OpAmp. Take for example AD8055 which can be powered by dual or single voltage supply. The specsheet describes IO characteristics for only dual power supply:

TA = 25°C, VS = ±5 V, RF = 402 Ω, RL = 100 Ω, Gain = +2, unless otherwise noted.

However, I wish to power this OpAmp with a single power supply. Let's say I will provide -Vs=0V and +Vs=5V. How do I determine IO characteristics than?

Here's another example: LT1818 OpAmp. They actually provide IO characteristics for dual and single power supplies:

TA = 25°C. (Note 9) VS = ±5V, VCM = 0V, unless otherwise noted

TA = 25°C. (Note 9) VS = 5V, 0V; VCM = 2.5V, RL to 2.5V unless otherwise noted

Now they introduced positive/negative notion for IO voltage. How to understand it? Is it the maximum/minimum voltages, voltages that used for Vin+ and Vin- respectively, or they omit the '-' sign for the negative voltages? It does implicitly say that on a single 5V supply, the output swings from 1V to 4V with a 100Ω load connected to 2.5V.

My video signal will will range +0.5V to +2.5V. I want to use any of these two OpAmps as buffers G=+1. I know that if I use dual +-5V power supply, they will work. However, I wish to stick to single +5V supply. Would any of them still do the buffer job for my video signal range?

• The second one will not swing below 0.8V (at Rl = 500 ohms) so ... probably no. (If Rl = several kilohms, maybe, but you don't specify that). The first will apparently not get closer than 1.8V of the negative rail, so, again ... no.
– user16324
Jun 13, 2014 at 17:04

You cant use AD8055 amplifier with single 5V supply because:

It needs at least 8V between + and - supply.

For LT1818 - im not sure where my red vertical line should be, please somebody confirm if I'm right or wrong.

In my opinion - this is "within the input common-mode voltage range":

Even if I'm wrong about "red vertical line" - this amplifier can't work with +0.5V signal at 0V at Vs- pin.

• Thank you. Clear enough. Let's see if anyone else has to add something. Jun 13, 2014 at 20:43

The front page of the data sheet tries to paint the best picture it can and on the front page for the AD8055 it says that the supply is +/- 5 volts. Look no further, this device is not suitable for +/- 2.5 volt supplies. End of story.

Look a little further if you must but on page 4 it shows this: -

You should also look at absolute max ratings too. One that can trip out is the maximum differential voltage between input pins - for this device it's +/-2.5 volts so don't go using as a comparator!!

"... However, I wish to power this OpAmp with a single power supply. Let's say I will provide -Vs= 0 V and +Vs = 5 V ..."

That is not sufficient to ensure the proper operation of your amplifier in single-supply mode. By holding the common-mode input voltage constant, the inverting-amplifier configuration eliminates common-mode-rejection errors. This is achieved by creating a positive floating voltage (typically Vcc/2) - called reference voltage applied to the non-inverting input, as shown in figure below:

Maintain that offset voltage away from ground and Vcc.

By not holding the common-mode input voltage constant, an example of circuit that is susceptible to errors due to violation of CMRR is the voltage follower configuration (unity-gain or buffer). Depending on the input voltage, the output may contain clipping or reach saturation.