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Lecture# Source Follower: Voltage Buffer

Description

This lecture covers the operation of a source follower stage, which acts as a voltage buffer to prevent gain reduction when driving low-impedance loads. It explains the large and small signal analysis of the source follower, including the voltage gain calculation and output resistance. The drawbacks of the source follower, such as nonlinearity and voltage headroom limitation, are discussed. Additionally, the lecture introduces the common-gate stage and its role in voltage-level shifting. The content also includes the large signal analysis of the common-gate stage, focusing on saturation conditions and voltage output calculations.

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In course

Instructor

EE-320: Analog IC design

Introduction to the design of analog CMOS integrated circuits at the transistor level. Understanding and design of basic structures.

Related concepts (75)

Cascode

The cascode is a two-stage amplifier that consists of a common-emitter stage feeding into a common-base stage. Compared to a single amplifier stage, this combination may have one or more of the following characteristics: higher input–output isolation, higher input impedance, high output impedance, higher bandwidth. In modern circuits, the cascode is often constructed from two transistors (BJTs or FETs), with one operating as a common emitter or common source and the other as a common base or common gate.

Current mirror

A current mirror is a circuit designed to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. The current being "copied" can be, and sometimes is, a varying signal current. Conceptually, an ideal current mirror is simply an ideal inverting current amplifier that reverses the current direction as well. Or it can consist of a current-controlled current source (CCCS).

Thévenin's theorem

As originally stated in terms of direct-current resistive circuits only, Thévenin's theorem states that "Any linear electrical network containing only voltage sources, current sources and resistances can be replaced at terminals A–B by an equivalent combination of a voltage source Vth in a series connection with a resistance Rth." The equivalent voltage Vth is the voltage obtained at terminals A–B of the network with terminals A–B open circuited.

Operational amplifier

An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to circuit ground) that is typically 100,000 times larger than the potential difference between its input terminals. The operational amplifier traces its origin and name to analog computers, where they were used to perform mathematical operations in linear, non-linear, and frequency-dependent circuits.

Digital signal processing

Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are a sequence of numbers that represent samples of a continuous variable in a domain such as time, space, or frequency. In digital electronics, a digital signal is represented as a pulse train, which is typically generated by the switching of a transistor.

Related lectures (106)

OTA Design: Small-signal AnalysisEE-520: Low-power analog IC design

Explores OTA and OPAMP design principles, small-signal analysis, and compensation techniques for stability and performance.

CG: IC Design IEE-320: Analog IC design

Covers BJT and MOS transistors, amplifiers, differential pairs, practical exercises, and cascode stages in IC design.

Cascode: Output Impedance and Gain AnalysisEE-320: Analog IC design

Covers the analysis of cascode circuits, focusing on output impedance and gain calculations.

Source Follower: Voltage Buffer & Level ShifterEE-320: Analog IC design

Explores the source follower as a voltage buffer and level shifter.

Common-Gate Stage: Analysis and Cascode TopologyEE-320: Analog IC design

Covers the analysis of the common-gate stage and introduces the cascode topology.