Microelectronics - Differential Amplifiers

MOS and Bipolar Differential Amplifiers

What you'll learn

To build a deep understanding of MOS differential amplifiers through intuitive explanation, rigorous analysis, and practical circuit modeling.

Learners will analyze, design, and troubleshoot MOS differential amplifiers, understanding large- and small-signal behavior under realistic operating conditions

Avoiding frequency response ensures focused mastery of static behavior; risks include misinterpreting region boundaries or neglecting mismatch effects.

Master differential pair operation, derive gain and output resistance, and analyze active load and current mirror structures using MOS small-signal models.

Requirements

Udemy Course Series on "Microelectronics" By Payam Heydari

Description

This audiobook course delivers a rigorous and intuitive understanding of one of the most foundational building blocks in analog integrated circuit design: the differential amplifier. Tailored for students, educators, and practicing engineers, this course explores the structure, operation, and analytical modeling of MOS-based differential amplifiers, from basic principles to advanced circuit configurations. The course emphasizes strong physical insight, step-by-step derivations, and thoughtful conceptual connections across the key operating regions of MOS transistors. Frequency response is intentionally excluded to focus exclusively on core operating behavior in the time-invariant domain.The course begins with the motivation behind differential signaling. We introduce listeners to real-world scenarios—such as rejecting power supply ripple or common-mode interference—that make differential amplifiers indispensable in analog, RF, and mixed-signal design. Through detailed narrative examples, we demonstrate how differential circuits cancel noise while maintaining linearity and signal integrity, even in noisy environments.We then revisit the essential operation of MOS transistors, focusing on the saturation and triode regions. The listener is guided through critical concepts such as threshold voltage, overdrive voltage, and current equations, with attention to the distinctions between weak, moderate, and strong inversion. These foundational topics are woven into the discussion of differential pair behavior, making the transition from single-transistor operation to multi-transistor systems seamless and conceptually natural.With these basics established, the course moves into the heart of the differential amplifier: the long-tailed pair. Listeners are first introduced to the symmetrical structure of the MOS differential pair with a constant tail current source. We carefully analyze its large-signal behavior, mapping out current-steering characteristics, output voltage swing, and transition regions. Through step-by-step narration, we cover the five key operating cases—from fully unbalanced inputs to ideal symmetry—and explain how the current redistributes between transistors based on the differential input voltage.Once the large-signal foundation is laid, we shift to small-signal analysis of differential pairs. Listeners learn how to compute differential-mode gain using standard small-signal models, derive expressions for output voltages, and understand the role of transconductance and output resistance. We highlight how the MOS differential pair achieves high gain and excellent common-mode rejection when device symmetry is preserved. Special attention is given to intuitive gain estimation, avoiding unnecessary mathematical complexity while preserving analytical rigor.Real-world imperfections are then introduced: mismatches between transistor parameters and load resistors. The course walks through the impact of non-identical devices, calculating how differential gain degrades when load resistors are unequal or transistors are not matched. Two different analysis methods—conventional small-signal modeling and superposition—are presented to give learners a flexible toolkit for circuit analysis.We then expand our study to include active loads, examining how using transistors instead of resistors can boost gain without sacrificing output swing. We compare passive and active load implementations and discuss the trade-offs in layout, linearity, and design complexity. From this foundation, the course introduces the current mirror load differential amplifier, one of the most widely used topologies in analog IC design.In this configuration, we explore how the current mirror not only serves as an active load but also acts as a differential-to-single-ended converter. We explain why half-circuit analysis fails in this case and instead develop a detailed two-port model that captures the amplifier's behavior. Through current flow analysis and KCL application, listeners derive expressions for output current, gain, and effective resistance. The result is a practical understanding of how modern op-amps and analog front-ends use current mirrors to interface differential stages with single-ended loads.Finally, the course concludes with a discussion of common-mode behavior. We explain how common-mode input voltages affect transistor biasing, current source operation, and overall amplifier linearity. We provide bounds for acceptable common-mode input ranges and discuss the design techniques used to prevent saturation or cutoff in improperly biased stages.Throughout the course, every derivation, concept, and insight is presented with clarity, pacing, and narrative structure optimized for auditory learning. No prior knowledge of frequency response is assumed or required, allowing listeners to focus fully on understanding the static and large-signal characteristics of differential amplifiers.

Overview

Section 1: Microelectronic Circuits - Differential Amplifier

Lecture 1 Why Differential Signaling?

Section 2: Microelectronic Circuits - Differential Amplifier

Lecture 2 Advantages of Differential Signaling?

Section 3: Microelectronic Circuits - Differential Amplifier

Lecture 3 Towards Differential Amplifier Topology - Part 1

Section 4: Microelectronic Circuits - Differential Amplifier

Lecture 4 Towards Differential Amplifier Topology - Part 2

Section 5: Microelectronic Circuits - Differential Amplifier

Lecture 5 Qualitative Large-Signal Analysis in MOS Differential Amplifiers

Section 6: Microelectronic Circuits - Differential Amplifier

Lecture 6 Common-Mode Operation for All Input Levels in MOS Differential Amps - Part 1

Section 7: Microelectronic Circuits - Differential Amplifier

Lecture 7 Common-Mode Operation for All Input Levels in MOS Differential Amps - Part 2

Section 8: Microelectronic Circuits - Differential Amplifier

Lecture 8 Quantitative Large-Signal Analysis in MOS Differential Amplifiers

Section 9: Microelectronic Circuits - Differential Amplifier

Lecture 9 MOS Differential Amplifiers - Large-Signal Analysis and Half-Circuit Model

Section 10: Microelectronic Circuits - Differential Amplifier

Lecture 10 Half-Circuit Model in MOS Differential Amplifiers

Section 11: Microelectronic Circuits - Differential Amplifier

Lecture 11 MOS Differential Amplifier: Sample Problem 1 and Solution

Section 12: Microelectronic Circuits - Differential Amplifier

Lecture 12 Qualitative Large-Signal Analysis in Bipolar Differential Amplifiers

Section 13: Microelectronic Circuits - Differential Amplifier

Lecture 13 Common-Mode Operation for All Input Levels in Bipolar Differential Amps

Section 14: Microelectronic Circuits - Differential Amplifier

Lecture 14 Quantitative Large-Signal Analysis in Bipolar Differential Amplifiers

Section 15: Microelectronic Circuits - Differential Amplifier

Lecture 15 Half-Circuit Model in Bipolar Differential Amplifiers

Section 16: Microelectronic Circuits - Differential Amplifier

Lecture 16 Impacts of Components Mismatch on Differential Amplifier's Performance - Part 1

Section 17: Microelectronic Circuits - Differential Amplifier

Lecture 17 Impacts of Components Mismatch on Differential Amplifier's Performance - Part2

Section 18: Microelectronic Circuits - Differential Amplifier

Lecture 18 Differential Amplifier with Active Load and Mirror Mirror

Section 19: Microelectronic Circuits - Differential Amplifier

Lecture 19 Differential Amplifier with Active Current Mirror - Gm Calculation

Section 20: Microelectronic Circuits - Differential Amplifier

Lecture 20 Differential Amplifier with Active Current Mirror - Rout and Gain Calculations

Section 21: Microelectronic Circuits - Differential Amplifier

Lecture 21 Differential Amplifier with Active Load: Sample Problem 1 and Solution

Undergraduate and graduate students in electrical and computer engineering and design engineers