TF EIM Chapt9

Operational Amplifiers (Op Amps)

The operational amplifier is monolithic (single chip) integrated circuit composed of transistors, resistors, diodes, and other components.

The small package produces a device with small capacitance and inductance which is superior to assembling the equivalent circuit with individual components.

Op-Amp

the "-" sign indicates the inverting input terminal and the "+" indicates the non-inverting input.

A positive going input voltage at the non-inverting ("+") input produces a positive going output.

A positive going input voltage at the inverting ("+") input produces a negative going output.

In other words the output is in phase when the input is non-inverting and 180 degrees out of phase when the input is inverting.

Equivalent circuit

Gain = [math]A_o \equiv \frac{V_{out}}{V_2-V_1}[/math]

Common Mode

Common mode input is defined as the situation where the two inputs are equal ([math]V_1 = V_2)[/math]. In this case[math] V_1[/math] is inverted and will cancel the input [math]V_2[/math] so the output becomes Zero in the ideal Op Amp.

Op Amps usually has two bias supplies in order to produce a high gain as determined by the difference in the input voltages. The output can't be larger than the supply bias.