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.
Basics of Differential Amplifiers
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Welcome everyone! Today we're going to dive into differential amplifiers. Can anyone tell me why we use differential amplifiers instead of regular amplifiers?
I think itβs because they can reject noise that is common to both inputs?
Exactly! That's one of the main advantages. The ability to amplify the difference between two signals while rejecting common ones is key to their function. This brings us to the concept of the Common Mode Rejection Ratio or CMRR.
What does CMRR indicate specifically?
Great question! CMRR indicates how well an amplifier rejects common signals compared to how well it amplifies differential signals. A high CMRR means better performance in rejecting noise.
So, higher values of CMRR are better?
Correct! A higher CMRR means the amplifier will perform better in noisy environments.
How do we ensure high CMRR in a differential amplifier?
We can achieve that by using matched components and including current mirrors as they improve gain stability. Let's explore how current mirrors are employed!
Role of Current Mirrors
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Current mirrors play a critical role. Can anyone describe what a current mirror does?
I believe it mirrors the current from one branch to another, keeping the currents equal?
Precisely! This ensures that the reference current is the same across different parts of the circuit, allowing for accurate amplification. Anyone recall what happens when we combine current mirrors with differential amplifiers?
Using current mirrors can increase both common mode and differential gains, right?
That's right! They help improve the overall performance of the amplifier. Can someone explain how that affects CMRR?
If both gains increase, but the ratio remains constant, doesnβt that maintain or enhance CMRR?
Exactly! We should always aim to keep that ratio favorable for robust amplifier design.
Analyzing Small Signal Models
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Now let's analyze small signal models for these circuits. What do you think we can learn from this analysis?
I think we can find the gains of the respective modes?
Absolutely! By breaking the circuit down to its small signal equivalent, we can derive those gains. Remember, the common mode gain affects CMRR directly.
How do we calculate these gains practically?
We use the small signal parameters and summarize each gain. For instance, we might use transconductance and load resistance to establish our equations.
Is it often possible to simplify these models?
Yes, often we can make approximations that streamline the calculations without losing too much accuracy.
So, the end goal is always to maximize CMRR?
Correct! Remember, our analysis should always keep CMRR performance in mind.
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 functionality of differential amplifiers, highlighting how current mirrors in BJTs influence both differential and common mode gains. It explains the importance of CMRR, the relationship between common and differential mode gains, and the implications of active loads on performance.
Detailed
Common Mode Rejection Ratio
This section examines the Common Mode Rejection Ratio (CMRR) in differential amplifiers, primarily focusing on BJTs and current mirror configurations. CMRR is a critical parameter that determines the ability of the circuit to reject common mode signals while amplifying differential signals.
Key Concepts:
- Differential Amplifier Structure: Unlike simple amplifiers, differential amplifiers are designed to amplify the difference between two input signals while rejecting any signals common to both inputs.
- Current Mirrors: The use of current mirrors in setting the tail current of the differential amplifier enhances its linearity and stability. The tail current is influenced by reference currents and potential losses.
- Common Mode and Differential Mode Gains: The common mode gain increases while the differential gain also potentially improves with the addition of active loads, which helps maintain signal integrity. The ratio of these two gains defines CMRR, which is vital for ensuring that interference does not affect the signal being amplified.
This section lays the foundation for understanding how different configurations impact amplifier performance, making it essential for future discussions on robust circuit design.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Definition of Common Mode Gain Ratio
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, just for completeness modified common mode gain it becomes with a β ( ) sign and this β . So, this is in comparison with the previous circuit gain, common mode gain, it was β .
Detailed Explanation
In this text, the modified common mode gain is being defined. The symbol indicates that the common mode gain has a negative sign when compared to the previous circuit's gain, showing a decrease in gain or a change in behavior due to the modifications made, particularly through the use of a current mirror.
Examples & Analogies
Consider a tuning dial on a radio. If you adjust the dial in a certain way, the radio might pick up a stronger signal (like common mode gain). If you adjust it too far, you might lose the signal altogether (as indicated by the negative sign), similar to how changing circuit configurations can improve or worsen gain.
Improvements in Differential and Common Mode Gain
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, to summarize we have replaced both the active load part and the tail part it is getting in fact, current mirror. So, that makes the differential mode gain and common mode gain getting improvised.
Detailed Explanation
This section reflects on the benefits of replacing parts of the circuit with a current mirror. By substituting the active load and tail parts with a current mirror, both the differential mode gain (the circuit's ability to amplify differences in input signals) and the common mode gain (the circuit's ability to respond to signals common to both inputs) have shown improvement.
Examples & Analogies
Think of it like upgrading an old bicycle to a newer model with better gears. The new gears allow you to pedal more efficiently on different terrains (improved differential mode gain) while still maintaining balance on flat ground (improved common mode gain).
Maintaining Current Balance
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
As a result we can maintain the good balance of this current and this current together with whatever the current is flowing through transistor-3.
Detailed Explanation
This part discusses the necessity of balancing the currents flowing through the circuit, particularly in the newly configured current mirror circuit. Maintaining this balance is crucial for the circuit to function correctly, ensuring that each transistor receives the appropriate amount of current to amplify signals effectively.
Examples & Analogies
Consider a seesaw at a playground. For it to balance, both sides need equal weight. If one child is heavier, the seesaw tilts. Similarly, if the current in the transistors isnβt balanced, it can lead to ineffective circuit operations.
Ratio Significance: Common Mode Rejection Ratio
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
In fact, the ratio is important which is referred as common mode rejection ratio.
Detailed Explanation
The importance of the common mode rejection ratio (CMRR) is highlighted here. CMRR represents the ability of a differential amplifier to reject common signals that affect both inputs equally while amplifying the differences between them. A high CMRR indicates good performance, as it shows the differential amplifier can effectively ignore noise that affects both inputs in the same way.
Examples & Analogies
Think of CMRR like an advanced filtering system in a music application. If both speakers (inputs) start picking up a static noise (common signal), a good filter will allow the music (the difference) to be heard clearly while ignoring the unwanted static (common signals), hence it will have a high CMRR.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
-
Differential Amplifier Structure: Unlike simple amplifiers, differential amplifiers are designed to amplify the difference between two input signals while rejecting any signals common to both inputs.
-
Current Mirrors: The use of current mirrors in setting the tail current of the differential amplifier enhances its linearity and stability. The tail current is influenced by reference currents and potential losses.
-
Common Mode and Differential Mode Gains: The common mode gain increases while the differential gain also potentially improves with the addition of active loads, which helps maintain signal integrity. The ratio of these two gains defines CMRR, which is vital for ensuring that interference does not affect the signal being amplified.
-
This section lays the foundation for understanding how different configurations impact amplifier performance, making it essential for future discussions on robust circuit design.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
-
Example of a differential amplifier used in audio equipment to enhance sound quality by rejecting noise.
-
A practical application of current mirrors in ensuring bias stability in integrated circuits.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
-
CMRR is key, listen and see, Higher means better, noise won't bother.
π Fascinating Stories
-
Picture a differential amplifier as a pair of noise-canceling headphones; it only lets through the sound differences while filtering out background noise.
π§ Other Memory Gems
-
C β Common signals, M β Must be rejected, R β Ratio of gains, R β Reinforces performance.
π― Super Acronyms
Don't forget CMRR stands for
- C: β Common
- M: β Mode
- R: β Rejection
- R: β Ratio.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Common Mode Rejection Ratio (CMRR)
Definition:
A measure of an amplifier's ability to reject input signals common to both inputs, defined as the ratio of differential gain to common mode gain.
-
Term: Differential Amplifier
Definition:
An amplifier that amplifies the difference between two input voltages while rejecting any voltage common to both inputs.
-
Term: Current Mirror
Definition:
A circuit configuration that provides a constant current to a load while maintaining a relationship to a reference current.
-
Term: Gain
Definition:
The ratio of output signal to input signal in an amplifier.