BJT and Op-Amp Basics Course

Lesson 1 • BJT Operating Regions

Defines cutoff, active, saturation, and reverse-active regions using junction bias states. Connects region selection to amplifier vs. switch applications.

Lesson 2 • Semiconductor Physics Review

Covers atomic bonding, intrinsic/extrinsic semiconductors, and carrier behaviour. Establishes the physics basis needed to understand BJT junction operation.

Lesson 3 • Current Gain and Basic BJT Equations

Derives alpha, beta, and the Ebers-Moll current relationships. Students can calculate terminal currents given bias conditions and device parameters.

Lesson 4 • P-N Junction Fundamentals

Explains depletion region formation, built-in potential, and diode I-V behaviour. Provides the junction theory that directly underlies BJT operation.

Lesson 1 • Importance of the Q-Point

Explains why a stable quiescent point is critical for linear amplification. Connects Q-point location on the load line to signal swing and distortion.

Lesson 2 • Emitter-Stabilised Bias

Introduces the emitter resistor as a feedback element that reduces Q-point sensitivity. Students derive stabilised bias equations and compare results to fixed bias.

Lesson 3 • Fixed-Bias Configuration

Analyses the single-resistor base-bias circuit and its sensitivity to beta. Students calculate Q-point values and identify stability limitations.

Lesson 4 • Potential-Divider Bias

Covers the most widely used bias network and its near-beta-independent Q-point. Students apply exact and approximate analysis methods.

Lesson 1 • AC Equivalent Circuit Concepts

Explains how DC sources and coupling capacitors are replaced in AC analysis. Establishes the superposition principle separating DC bias from AC signals.

Lesson 2 • Input and Output Impedance

Derives input and output impedance expressions for each BJT configuration. Students use impedance values to assess loading effects in multi-stage designs.

Lesson 3 • Hybrid-Pi Small-Signal Model

Derives the hybrid-pi model parameters from BJT physics and the Q-point. Students calculate transconductance, input resistance, and output resistance.

Lesson 4 • H-Parameter Model

Introduces the two-port h-parameter representation and its relationship to hybrid-pi. Students convert between parameter sets and use datasheets effectively.

Lesson 1 • Common-Collector (Emitter Follower)

Covers the CC stage as a unity-gain voltage buffer with high input and low output impedance. Students apply it for impedance transformation between stages.

Lesson 2 • Common-Base Amplifier

Analyses the CB stage for current gain near unity, low input impedance, and high bandwidth. Students identify its use in high-frequency and current-input applications.

Lesson 3 • Common-Emitter with Emitter Degeneration

Examines the effect of an unbypassed emitter resistor on gain, linearity, and impedance. Students trade gain for improved stability and bandwidth.

Lesson 4 • Configuration Comparison and Selection

Summarises gain, impedance, and bandwidth trade-offs across all three configurations. Students apply selection criteria to match topology to system requirements.

Lesson 1 • Low-Frequency Response Analysis

Derives lower cutoff frequencies caused by coupling and bypass capacitors using short-circuit time constants. Students calculate each capacitor's contribution to the lower -3 dB point.

Lesson 2 • Bode Plot Construction

Teaches systematic construction of asymptotic Bode magnitude and phase plots. Students sketch complete frequency response from pole and zero locations.

Lesson 3 • High-Frequency Response Analysis

Examines internal BJT capacitances C_pi and C_mu and their effect on high-frequency gain. Students apply the Miller effect and open-circuit time constants to find the upper cutoff.

Lesson 4 • Multi-Stage Frequency Response

Extends single-stage analysis to cascaded amplifiers and their combined bandwidth. Students apply the bandwidth shrinkage formula and identify the dominant stage.

Lesson 1 • Ideal Op-Amp Model

Defines the ideal op-amp with infinite gain, infinite input impedance, and zero output impedance. Students use the ideal model as the starting point for all circuit analysis.

Lesson 2 • Virtual Short and Virtual Open Principles

Derives the virtual short and virtual open rules from negative feedback and ideal gain. Students apply these rules to simplify closed-loop circuit analysis.

Lesson 3 • Key DC Specifications

Covers input offset voltage, bias current, offset current, and CMRR as critical DC error sources. Students calculate output error contributions from each parameter.

Lesson 4 • Op-Amp AC Specifications

Introduces gain-bandwidth product, slew rate, and full-power bandwidth as AC performance limits. Students determine whether an op-amp meets signal frequency and amplitude requirements.

Lesson 1 • Summing and Difference Amplifiers

Extends the inverting topology to weighted summing and derives the difference amplifier for differential signals. Students design audio mixing and bridge sensor circuits.

Lesson 2 • Integrator and Differentiator Circuits

Replaces feedback or input resistors with capacitors to perform mathematical integration and differentiation. Students analyse frequency response and practical stability issues.

Lesson 3 • Instrumentation Amplifier Design

Builds the three-op-amp instrumentation amplifier for high CMRR and adjustable gain. Students apply it to differential sensor signal conditioning.

Lesson 4 • Inverting Amplifier Configuration

Derives closed-loop gain, input impedance, and output impedance for the inverting topology. Students design resistor networks for specified gain and input resistance.

Lesson 1 • Stability Criteria and Phase Margin

Applies the Barkhausen criterion and Bode plot analysis to determine closed-loop stability. Students calculate phase margin and gain margin from loop gain plots.

Lesson 2 • Frequency Compensation Techniques

Covers dominant-pole, lead, and lag compensation methods to restore adequate phase margin. Students modify op-amp circuits to achieve stable closed-loop operation.

Lesson 3 • Practical Op-Amp Limitations

Addresses finite gain, output voltage swing, output current limits, and noise in real op-amps. Students derate ideal designs to account for real device constraints.

Lesson 4 • Op-Amp Selection and Layout Guidelines

Guides selection of op-amps based on supply voltage, bandwidth, noise, and power. Students apply PCB layout best practices to minimise parasitic effects.