Professional Courses
Industry-relevant training in Business, Technology, and Design to help professionals and graduates upskill for real-world careers.
Categories
Interactive Games
Fun, engaging games to boost memory, math fluency, typing speed, and English skillsβperfect for learners of all ages.
Typing
Memory
Math
English Adventures
Knowledge
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Introduction to Current Mirrors
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Welcome class! Today we're focusing on current mirrors. Can anyone tell me what a current mirror is?
Isn't it a circuit that provides a constant current output?
Exactly! A current mirror is designed to produce a current that matches a reference current. This is essential in analog circuits. Letβs use the acronym 'MIRROR' to remember this: 'Mirrors Input's Reference, Replicating Output Ratios'.
How does this work in practical circuits?
Good question! The current mirror can be configured with BJTs or MOSFETs, and today we'll look at both to understand their applications.
Small Signal Model for DC Conditions
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Letβs talk about the small signal model under DC conditions. When no signals are present, how does the current mirror behave?
It behaves like an open circuit since the AC component is absent.
Correct! In this case, the small signal equivalent circuit simplifies greatly. Can anyone remind us of the significance of voltage dependent current sources?
They represent the small variations in output current based on input changes.
Precisely! Understanding these small signal characteristics will help when we apply current mirrors in amplifiers.
Small Signal Model with AC Input
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Now, let's explore the scenario when the current mirror carries an AC signal. What changes occur?
The AC input will affect the output current, right?
Exactly! This means our small signal circuit needs to include the signal components, and we will analyze how these influence the circuit performance.
What does that look like in an equation?
Good question! We'll often express voltage across the load as a function of the input current, as critical in analyzing the amplifier stages.
Applications in Amplifiers
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Next, letβs discuss where current mirrors are applied, particularly in amplifiers. How might they serve in these circuits?
They can replace passive loads, increasing gain, right?
Exactly! They help with matching currents and improving linearity. In a common emitter configuration, they act as active loads, which provide several advantages.
What about when matching components in a circuit?
Great point! Matching components accurately is a real challenge in practice, but in IC design, itβs often easier to achieve because transistors can be fabricated together.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The section delves into the small signal model of current mirrors, detailing how these models can be applied to both BJT and MOSFET circuits. It emphasizes understanding the circuit under DC conditions as well as when it carries signal currents, with applications in amplifiers and differential circuits.
Detailed
Detailed Summary
In this section, we explore the small signal model analysis of current mirrors, which are essential components in analog electronic circuits. A current mirror's small signal model allows us to understand how variations in input signals affect the current output, simplifying complex circuit analyses.
Key Points:
- The section begins by introducing the current mirror concept and its basic configuration using transistors (BJT and MOSFET).
- We differentiate two scenarios: one where the current mirror operates under DC conditions (no signal) and the other where it carries AC signal currents.
- For both BJT and MOSFET implementations, we derive small signal equivalent circuits, demonstrating how to extract meaningful parameters such as voltage-dependent current sources and resistances.
- The small signal equivalent circuit is crucial when calculating the transfer function of a circuit containing a current mirror.
- Applications of these models in common emitter and common source amplifiers are discussed, highlighting how current mirrors can serve as active loads or biasing elements in these configurations.
- Lastly, the potential challenges with matching components in real circuits versus theoretical assertions are discussed, emphasizing the importance of practical design considerations.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Introduction to Small Signal Models
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
We need to understand the small signal model of current mirror and to go into the small signal model we do have two possible situations: one is the current mirror may not be carrying any signal namely under DC condition what is the small signal equivalent circuit and then we do have the second possible situation where the current mirror may carry signal in the form of current.
Detailed Explanation
In electronic circuits, particularly when analyzing amplifiers, we often use small signal models to simplify calculations. The small signal model represents the behavior of the circuit under small variations around a DC operating point. There are two situations to consider: 1) When the circuit is in a DC state without any AC signals (i.e., it isn't amplifying any signal). In this case, we determine how the circuit behaves just based on the DC values. 2) When the circuit does have an input signal, which could be an AC current or voltage applied to the circuit. This results in a different analysis because we need to account for the variations due to the signal.
Examples & Analogies
Think of a small signal model like analyzing the effect of a bump in a flat road. When the road is flat (DC condition), we can predict how a car moves smoothly on it. However, when there is a bump (AC signal), we have to analyze how the car reacts β the vibration, speed change, etc. just like the circuit reacts to the input signal.
Small Signal Model with MOSFETs
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
We do have the current mirror circuit, we do have transistor-1; it is diode connected and the reference current DC current that is getting mirrored into this branch through this transistor-2 and here we do have the application circuit.
Detailed Explanation
In a current mirror circuit using MOSFETs, one transistor is connected in such a way that it sets a reference current through it, which is then mirrored by another transistor that is used in the application circuit. This configuration allows us to produce a consistent current output, matching the input reference current under DC conditions. We need to analyze how small signals affect this configuration by replacing the heavy components in the circuit with simplified representations.
Examples & Analogies
Imagine a perfectly balanced scale at a market. The first weight that sets the balance is like the reference current. The scale measures other weights (the mirrored current) against the reference weight. If you add a tiny weight (small signal) to one side, the balance shifts slightly, and we study how that affects the balance β that's similar to how we analyze small variations in electrical signals.
Open Circuit Condition for Small Signals
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
For small signal model this is DC current so; obviously, we have to make the current here it is since it is 0. So, we can say it is this circuit is open.
Detailed Explanation
When analyzing a small signal model, if the DC current is at zero (or in a situation that has no input signal), we treat the input as an open circuit. This simplification means we disregard any AC signal effects and only focus on the DC components. Due to this simplification, we can conclude that some voltages in the circuit will also be zero, making it easier to derive the small signal equivalent circuit without the complexity of active components.
Examples & Analogies
Think of it like a water line with no water flowing (representing the open circuit condition). If no water is flowing, you can ignore the connections and only visualize the pipes intact, making it easier to determine how it would behave if water were to flow at a later time.
Modeling with Signal Inputs
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
Now, if we want to analyze a situation where the current mirror has an input current (AC signal), we need to consider how the signal interacts with this DC current.
Detailed Explanation
In this case, when we introduce an AC signal current into the current mirror, we have to carefully analyze how this input affects the output through its interactions with the existing DC conditions. We represent these interactions with voltage-dependent current sources and resistance, creating an accurate representation of how signals affect the circuit's operation.
Examples & Analogies
Imagine a conveyor belt in a factory where boxes (the signal) are added occasionally on top of a fixed weight of boxes already on it (the DC component). As the input changes, the force on the conveyor changes too, altering the overall behavior of how quickly the boxes move down the line. This is similar to how small signals influence the output in electrical circuits.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
-
Small Signal Model: Used to analyze how input signals affect outputs in linearized circuits.
-
Current Mirrors: Essential elements in amplifiers that help in current replication and biasing.
-
DC vs. AC Analysis: Different conditions under which current mirrors operate, with specific models for each.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
-
In a common emitter amplifier, a BJT current mirror may replace the traditional load resistor to enhance performance.
-
In a MOSFET common source amplifier, a current mirror can provide stability and improved linearity.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
-
A current mirror's duty, not too blurry, it copies with no fuss, just as you trust, in circuits, itβs a must!
π Fascinating Stories
-
Imagine a mirror in a fancy circuit ball, reflecting currents big and small. It makes sure the flows always match, so amplifiers can dance and scratch!
π§ Other Memory Gems
-
Remember 'CAMP' for Current Analysis of Mirrors and Performance.
π― Super Acronyms
Use 'MIRROR' to recall
- Mirrors Input's Reference
- Replicating Output Ratios.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Current Mirror
Definition:
A circuit configuration that produces an output current equal to a specified reference current.
-
Term: Small Signal Model
Definition:
A linearized model of a circuit that ignores non-linear effects for small variations around a stable bias point.
-
Term: DC Conditions
Definition:
Operating conditions of a circuit without any alternating current (signal).
-
Term: AC Signal
Definition:
An alternating current signal that varies with time.
-
Term: Active Load
Definition:
A load that utilizes a current source instead of a resistor to increase gain and improve linearity.