Consider the inverting amplifier shown in Figure PI4.16....

Name: Problem 16, Chapter 14: Electrical Engineering: Principles and Applications
Uploaded: 2021-11-22T12:44:36-08:00
Duration: 2 min 9 s
Channel: Narayan Hari
Description: Consider the inverting amplifier shown in Figure PI4.16. Assuming an ideal op amp solve for the currents and voltages shown. According to Kirchhoffs current law, the sum of the currents entering a closed surface must equal the sum of the currents leaving. Explain how the law is satisfied for the closed surface shown when we use a real op amp in this circuit

Consider the inverting amplifier shown in Figure PI4.16. Assuming an ideal op amp solve for the currents and voltages shown. According to Kirchhoffs current law, the sum of the currents entering a closed surface must equal the sum of the currents leaving. Explain how the law is satisfied for the closed surface shown when we use a real op amp in this circuit

Key Concepts

Inverting Amplifier Configuration

The inverting amplifier is a foundational op amp circuit where the input voltage is applied to the inverting input through a resistor, and the noninverting input is typically grounded. A feedback resistor connects the output back to the inverting input, and together they determine the gain of the circuit. Analyzing this circuit using node analysis typically involves applying KCL at the inverting node to relate the currents through the input and feedback resistors.

Kirchhoff's Current Law (KCL)

Kirchhoff's Current Law states that the total current entering any junction in a circuit must equal the total current leaving that junction. This principle, which is a direct result of the conservation of electric charge, is essential for node analysis in all circuit configurations and guarantees that the sum of the currents on a closed surface is zero when all currents (including any small leakage or bias currents) are accounted for.

Real Op Amp Non-idealities

While ideal op amps are modeled with infinite input impedance (resulting in zero input bias current), real op amps exhibit finite input impedance and small input bias currents. These bias currents flow into the op amp’s input and must be included in the KCL analysis for any closed surface encompassing the input node. The presence of these small currents, even though they are typically negligible compared to the main signal currents, ensures that KCL is fully satisfied in a real-world circuit.

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