3.2:
Characteristics of OpAmp
Consider the equivalent circuit model of an operational amplifier. The output section consists of a voltage-controlled source in series with the output resistance.
In the input section, v1 and v2 denote voltages from the inverting and non-inverting terminals to the ground, respectively.
The output voltage of an op amp equals the product of the input voltage difference and the open-loop gain.
For small voltage differences, the op amp behaves linearly. If the voltage exceeds the power supply voltage the op amp saturates.
The combination of applied voltage and negative feedback ensures that the op amp operates within its linear range.
Modern amplifiers have large gains and input resistance, allowing them to be approximated as ideal op amps.
An ideal op amp has infinite open-loop gain, infinite input resistance, and zero output resistance. Both input terminal currents and the input offset voltage are zero in an ideal op amp.
Additionally, It has infinite bandwidth, allowing it to amplify signals of any frequency, and infinite slew rate, signifying its ability to change the output voltage rapidly over time.
3.2:
Characteristics of OpAmp
The operational amplifier, commonly known as an op-amp, is a specially designed electronic circuit component. Its purpose is to work in conjunction with other circuit elements to execute a defined signal-processing operation. Consider an equivalent circuit model of an op-amp, as depicted in Figure 1; the output section comprises a voltage-controlled source in parallel with the output resistance Ro.
Figure 1: The equivalent circuit of the nonideal op-amp
Figure 1 shows that the input resistance Ri equates to the Thėvenin equivalent resistance observable at the input terminals. Similarly, the output resistance Ro corresponds to the Thėvenin equivalent resistance discernible at the output. The differential input voltage (vd) is calculated as the difference between the noninverting terminal's voltage relative to the ground and the inverting terminal's voltage relative to the ground.
The op-amp discerns the difference between these two inputs and amplifies it by the gain A, thus generating a voltage that appears at the output. Here, A represents the open-loop voltage gain – named so because it signifies the gain of the op-amp in the absence of any external feedback from the output to the input.
Feedback is an integral concept to comprehend when studying op-amp circuits. Negative feedback can be achieved by feeding the output back to the op-amp's inverting terminal. When a feedback path from output to input exists, the resulting ratio of the output voltage to the input voltage is known as the closed-loop gain.
The op-amp does have its practical limitations. One such limitation is that the magnitude of its output voltage cannot surpass |VCC|. Essentially, the power supply voltage determines and restricts the output voltage. Depending on the differential input voltage, the op-amp can function in one of three modes: positive saturation, linear region, or negative saturation. If an attempt is made to increase vd beyond the linear range, the op-amp reaches saturation, yielding either vo = VCC or vo = –VCC.