# Dual Supply Voltages in Op-Amp Circuit & Op-Amp parameters

Why do we need dual supply voltages in Op-Amp circuits ?

Which parameter of Op-amp causes to make a square signal's shifting between 0-1,1-0 slower?

Sorry for grammar mistakes.

Why do we need dual supply voltages in Op-Amp circuits ?

You need dual supplies if your signal has a negative voltage portion and a virtual ground (DC offset superimposed on your signal) is not suitable.

Which parameter of Op-amp causes to make a square signal's shifting between 0-1,1-0 slower?

The slew rate defines how fast an op-amp can change its output level.

Strictly speaking, you don't need dual supply voltages. You can use a single supply connected to the op amp's rails. Dual supplies are generally much easier to work with, though, because you can easily set the op amp's common mode to ground. If you only have a single supply then you may need to generate a common mode voltage (e.g. at half the supply voltage), otherwise your input signal and/or output may be limited by one of the rails.

Consider this simple inverting amplifier with a single supply:

simulate this circuit – Schematic created using CircuitLab

The op amp's common mode voltage is ground, which is also the negative supply rail. This is often outside the op amp's input common mode range. Additionally, the op amp cannot produce a voltage at the output lower than ground, so any positive voltage at the input will be clipped (the op amp cannot drive the output below ground). To avoid this, you need to bias the non-inverting input to a voltage above ground (typically $V_{CC}/2$, to maximize the allowable voltage swing before the output is clipped at either rail). With dual supplies you already have a ground reference which you can use as the common mode voltage for the op amp's input, and if the supplies are balanced then ground is automatically at half the total supply voltage.