OPAMP AND ITS APPLICATION NUMERICAL PROBLEM | FEE | LECTURE 02 BY DR. GAURAV SAXENA | AKGEC

Value of the Information & Strength of the Argument

The informational value lies in the demonstration of a repeatable problem-solving procedure rather than in any new result. The lecturer shows how to reduce a multi-source op-amp network to a pair of node equations, which is the standard and pedagogically useful route: assume an ideal device, invoke the virtual ground, write KCL at each node, cancel the common resistance, and solve. The argumentation is deductive and self-consistent in its structure — each step follows from the previous one, and the choice of method is justified by the stated assumptions (no bias current, infinite CMRR, ideal device). The weakness is in execution rather than in logic: the numerical substitutions are spoken quickly and inconsistently, with resistor values that shift between the statement of the formula and its evaluation, and the final output voltage is never explicitly stated as a clean number. The descriptive segment on CMRR and ideal op-amp characteristics is a correct but purely textbook enumeration, delivered without derivation or physical intuition, and it contains at least one clear error in units (CMRR described in degrees rather than decibels) and one questionable claim (PSRR of an ideal op-amp stated as zero). The cascaded-amplifier problem is the most valuable part, because it forces the student to identify the function of each stage before computing, which is the actual skill being trained. Overall the argumentation is sound in method, weak in numerical rigour, and offers no critical discussion of when the ideal model breaks down.

Scientific Rigor, Source Quality, Title Accuracy

No external sources, textbooks, datasheets or references are cited at any point; the only links in the description are the college website and the course playlist, which are institutional and navigational rather than documentary. The scientific content therefore rests entirely on the lecturer’s authority and on the standardness of the material, which is genuinely standard — Kirchhoff’s law, the virtual-ground approximation and the ideal op-amp parameter list are uncontroversial and can be found in any introductory analog electronics text. The rigour problem is not conceptual but presentational: quantities are announced with slips (‘CMRR should be 90°’, ‘PSRR is zero’), the decibel formula is written as ‘20 log base 10 A by AC’ without clearly distinguishing Ad from Ac, and the numerical evaluations are not checked against a final answer. The title-to-content match is good: the video does consist of op-amp application numericals, and the lecture number and course context are correctly stated, though roughly a third of the runtime is a descriptive question rather than a numerical one.

The title accurately announces numerical op-amp application problems, and the video does solve such problems, although it also spends a substantial block on a purely descriptive question about CMRR and ideal op-amp characteristics.

6/10

The lecture is delivered by a named faculty member of an accredited engineering college and relies on standard, well-established circuit-analysis methods (Kirchhoff's current law, virtual ground, ideal op-amp assumptions). The technical content is orthodox and internally consistent, but the presentation is improvised and contains several slips (e.g. 'CMRR should be 90°', 'PSRR is zero', inconsistent resistor values between the stated and computed expressions), and no external references or textbook citations are given. Reliability is therefore moderate: the method is sound, the execution is imprecise.

Markers derived by PSI from the transcript: the creator did not define chapters.

• 00:30Introduction of the lecture and announcement that Unit 3 (op-amp and applications) numericals will be solved.
• 01:15Presentation of the first problem: a mixed summing amplifier, identified as a previous university examination question.
• 02:10Statement of the ideal op-amp assumptions: zero bias current, infinite CMRR, virtual ground.
• 03:20Application of Kirchhoff's current law at node 1, giving I1 + I2 = I3 and the node voltage Vx = 11/3 ≈ 3.66 V.
• 05:30Application of KCL at node 2 (I4 + I5 = I6) to derive the output voltage of the summing stage.
• 07:00Transition to the descriptive question: definition and meaning of the common-mode rejection ratio.
• 08:20CMRR expressed in decibels as 20 log10(Ad/Ac), with Ad the differential gain and Ac the common-mode gain.
• 10:20Enumeration of ideal op-amp characteristics: infinite input impedance, zero output impedance, infinite open-loop gain, infinite CMRR, infinite slew rate, infinite bandwidth, zero PSRR.
• 13:20Presentation of the cascaded circuit problem combining an inverting amplifier, an inverting summing amplifier and a difference amplifier.
• 15:50Computation of the first stage output as −6 V using Vo = −(Rf/Ra)·Vi, then setup of the summing and difference stages.

• AKGEC official website — Institutional site of Ajay Kumar Garg Engineering College, the institution hosting the lecturer and the course.
• Fundamentals of Electronics Engineering — course playlist — Playlist containing all five units of the course, referenced in the description as the companion material for this lecture.

• Operational amplifier — Wikipedia — Confirms the ideal op-amp assumptions (infinite input impedance, zero output impedance, infinite open-loop gain) and the standard inverting, summing and difference amplifier configurations used in the lecture.
• Common-mode rejection ratio — Wikipedia — Confirms the definition of CMRR as the ratio of differential gain to common-mode gain and its expression in decibels, matching the lecturer's presentation.

• Slew rate — Wikipedia — The lecture states that the slew rate of an ideal op-amp is infinite, which is a conventional idealisation, but real devices are limited by internal bias currents and compensation capacitors; the lecture gives no indication of this practical limitation, which could mislead students applying the ideal model to real circuits.