Microelectronics by Maurizio Paolo Emilio

Author:Maurizio Paolo Emilio
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

4.2 Main Configuration

An op-amp can use negative feedback to set the closed-loop gain as a function of the circuit external elements (resistors), independent of the op-amp gain, as long as the internal op-amp gain is very high. In Fig. 4.3 is shown an ideal op-amp in a non-inverting configuration with negative feedback provided by voltage divider R1, R2.

Fig. 4.3Non-inverting configuration

The op-amp with negative feedback forces the two inputs v+ and v− to have the same voltage, even though no current flows into either input. This is sometimes called a “virtual short.” As long as the op-amp stays in its linear region, the output will change up or down until v− is almost equal to v+. If v IN is raised, v OUT will increase just enough so that v− (tapped from the voltage divider) increases to be equal to v+ ( = v IN). The negative feedback forces the virtual short condition to occur.

An op-amp in the inverting configuration (with negative feedback) is shown in Fig. 4.4. Feedback is from v OUT to v− through resistor R2. v IN comes in to the v− terminal via resistor R1 and v+ is connected to ground [3, 4].

Fig. 4.4Inverting configuration

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