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.
Concept of Current Mirror in Circuit Design
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Today, we'll explore how a current mirror can help bias a common emitter amplifier. What do you think a current mirror does in such a setup?
I believe it maintains a constant current, right?
Exactly! The current mirror allows us to keep the bias stable, enabling better performance of the amplifier. Can anyone tell me why matching transistor parameters like Beta is vital?
If they donβt match, the current won't flow evenly?
Correct! Mismatched transistors lead to imbalances in current and could greatly impair performance.
Does that mean that if one transistor's Beta is higher, it might take over and cause saturation?
Yes, thatβs a real risk in practical applications! Remember to keep this in mind as we go into the calculations.
Calculating Collector Current (I_C)
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Letβs look at how to find the collector currents. If I state I_C should be 2 mA, what do you think comes next?
We should first confirm the biasing currents in the transistors.
Yes! That leads us to calculate the base current. Given Beta is 100, can anyone calculate the base current?
I_C = Beta x I_B, so I_B = I_C / Beta equals 20Β΅A.
Perfect! With that established, what would be our bias resistance R_B1 necessary to achieve this?
Using Ohm's law, R_B1 = V_B / I_B. If the voltage is about 12V, then we get 570 kβ¦!
Great work! Now thereβs an assumption we made that the base current losses are negligible, how does that influence our calculations?
If losses are considered, then the calculated values may not hold true, leading to deviations in actual performance.
Exactly! Now, let's summarize these calculations.
Understanding Voltage Gain and Output Resistance
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Next, letβs calculate voltage gain. What do you think the expression for voltage gain looks like?
Is it related to the output resistance and transconductance of the amplifier?
Exactly! The voltage gain AV equals g_m * R_out. Here, weβve calculated R_out as 25kβ¦. If our g_m is around 76.9 mS, it gives us a voltage gain close to 1923!
Thatβs a remarkably high gain for an amplifier!
What if the output voltage suddenly changes because of transistor variability?
Good point! In real-world applications, we see variations. Early voltage doesnβt always stay constant, affecting the gain.
So, if Beta changes, we need to recalculate everything again?
Precisely! Let's assess how much the voltage would shift with different Beta values.
Impact of Early Voltage in Circuit Performance
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Letβs transition to Early voltage effects. What do you think happens if transistors 3 and 4 have mismatched Early voltages?
The calculated output voltage would likely decrease since one transistor would dominate current flow?
Exactly right! If one has higher values, it would create a feedback effect on the circuit, affecting overall performance.
So, if we theoretically lower the output voltage to 10.95V due to Beta being higher, how does that impact the entire circuit?
It means our gain becomes less effective, and you could potentially saturate one transistor if the current requirements aren't met.
So, calibration of circuits often becomes necessary?
Absolutely! Precision in matching and maintaining thresholds becomes critical in amplifier design.
This makes designing amplifiers much more challenging than it seems!
Review and Real-World Implications
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Letβs recap. Today, we covered how to calculate collector currents and gain. Why do we care about these calculations in designing amplifiers?
To ensure they operate effectively without distortion?
Exactly! High gain, low distortion, and the right biasing are all part of creating reliable amplifiers.
And understanding the real impacts of variable parameters can save lots of headaches.
Very true! Always account for practical nuances in theory. Remember, precision matters!
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
In this section, a detailed numerical example is given, focusing on a common emitter amplifier that incorporates a current mirror for biasing. Various calculations, including collector current, output resistance, and voltage gain, are explored, along with practical implications of early voltage and transistor matching.
Detailed
Detailed Summary
This section continues with numerical examples focusing on the common emitter amplifier, utilizing a current mirror for biasing. The narrative outlines the calculation of the collector current and output voltage while assuming the transistors within the circuit are identical with a specified Beta (Ξ²) of 100.
The first key calculation is determining the collector current (I_C) for transistor-1 and transistor-4, both set to 2 mA. The teacher identifies the current through transistor-2 should match that of transistor-1, leading to the derivation of a bias resistance (
R_B1) of 570 kβ¦. As all devices operate in the active region, output resistance calculations follow, revealing an output resistance of 25 kβ¦ and a significant voltage gain of about 1923, which is notably high due to the active load factor.
The section then delves into the calculation of output voltage (V_OUT) at 11.4 V, considering Early voltage and confirming transistor current mirroring within the expected thresholds. A follow-up scenario examines conditions where the Beta of transistors-3 and 4 are increased to 250, highlighting how this affects current discrepancies and ultimately leads to an output voltage decrease to 10.95 V when excess current is needed.
This numerical exploration serves not only to demonstrate calculation procedures but also emphasizes the significance of transistor matching in precise circuit operations, setting the stage for future discussions on differential amplifiers.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Introduction to Next Numerical Example
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
As I said that the problem here is very similar, except that transistor-3 and transistor-4 they do have Ξ² = 250. Now, here we can try to find what will be the current I and I at V = 11.4.
Detailed Explanation
In this portion, we are introducing a new example that builds upon the previous discussions. The focus is on two transistors (transistor-3 and transistor-4) that have a current gain (Ξ²) of 250. The goal of this example is to calculate the currents (I) under the condition that the voltage V is set at 11.4V. By changing the Ξ² value of transistors, we can explore how this impacts the circuit behavior. This serves as a transition to the actual calculation of the currents.
Examples & Analogies
Imagine you are baking cookies, and you usually use a specific recipe with all the ingredients tightly controlled (like keeping Ξ² constant). Now, you decide to make a variation in one ingredient (like changing a type of flour) and want to see how it impacts the taste of your cookies. In a similar way, we are adjusting the Ξ² of the transistors here to see how it affects the current output.
Calculating Currents with New Ξ² Value
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
As I say that is the voltage here it is 11.4 and supposes if we make this voltage also 11.4, then we know this current and this current they will be equal.
Detailed Explanation
This chunk states that if we hold the voltage at 11.4V, we can assume that the currents through transistor-3 and transistor-4 will be equal. This is based on the principle that when two pathways are kept at the same voltage in a circuit, the current flowing through both should be the same under ideal conditions. Here, we're setting a reference voltage of 11.4V and assessing how it affects the operation of the transistors.
Examples & Analogies
Think of two water pipes that are both being filled from the same reservoir. If the pressure (akin to voltage in our case) is the same in both pipes, the amount of water (current) flowing through each should also be the same. If we adjust the pressure to match (11.4V), we predict similar flow rates in both paths.
Understanding Collector Currents
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
In fact, that is the base current 20 Β΅A Γ Ξ² that is 100 Γ ( ). In fact, if you do the calculation here what you will get it is the 2 Γ1.114.
Detailed Explanation
This portion explains how to calculate the collector current in transistor-3 by multiplying the base current (20 Β΅A) by the transistor's current gain (Ξ²). In this case, Ξ² is assumed to be 100 for calculations and when adjusted leads to a result of 2 times the value derived from the initial assumptions. This elucidates how input factors influence the output current through multiplication.
Examples & Analogies
Consider a factory where each worker is multiplied by a certain productivity factor (Ξ²). If each worker produces a certain number of items, the total output is calculated by multiplying the number of workers by their individual productivity rates. Similarly, here weβre multiplying the base current (20 Β΅A) by the efficiency factor (Ξ²) to find the overall current producedβillustrating how simple inputs can be scaled to show larger outputs.
Output Current and Voltage Drop Consideration
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
Now if you see this current is getting mirrored here ignoring the base current loss here, because for transistor-3 and transistor-4, we have considered their Ξ²βs are very high.
Detailed Explanation
The focus here is on the concept of current mirroring in transistors, particularly transistors-3 and -4, under the assumption that base current loss can be ignored because of the high Ξ² values. In a current mirror configuration, the output current ideally replicates the input current, with minimum loss. In practical scenarios, recognizing whether to consider losses helps in determining accurate current values.
Examples & Analogies
Imagine a perfect copy machine that duplicates every document exactly each time. However, if the machine has a slight fault, it might miss copying some small details (base current losses). In this case, we assume our machine works perfectly (high Ξ²) for simplicity, enabling us to focus on overall performance rather than the tiny imperfections.
Finalizing Output Voltage Calculations
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, the voltage here at the output the DC voltage = V = 11.4 β 0.45 = 10.95 V.
Detailed Explanation
In this final segment, the actual output DC voltage is calculated. With the adjustments made to account for excess current demand and other variations, the resulting output voltage is found to be 10.95V. This value is significant because it represents how every incremental change in current flow can lead to variations in output voltage. We conclude that precision in current management substantially impacts overall circuit functionality.
Examples & Analogies
Think of adjusting a garden hose to provide water to a plant. If too much water (current) is demanded by the plant, the pressure from the faucet (supply voltage) will lower, resulting in less water reaching the plant. In our example, as we assess the output voltage (supply), shifting parameters can lead to a noticeable drop (from 11.4V to 10.95V) showing just how sensitive our system can be!
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
-
Current Mirror: A configuration that maintains constant current across transistors.
-
Collector Current: Critical in determining the output performance of amplifiers.
-
Voltage Gain: High voltage gain is desired for effective amplification.
-
Early Voltage: Important factor in transistor performance that affects stability.
-
Transistor Matching: Essential for reliable operation in amplifiers.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
-
A common emitter amplifier using current mirrors can achieve high voltage gain as indicated by a calculated gain of 1923.
-
In practical applications, mismatched Early voltages of the transistors can lead to significant deviations in output current.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
-
To find current mirrors, be smart and steady; their constant flow keeps circuits ready.
π Fascinating Stories
-
Imagine twins at a race. If one runs fast, the other is sure to follow, keeping their pace. This is like a current mirrorβone transistor's current leads and the other matches its pace.
π§ Other Memory Gems
-
CVC - Current value constant, Voltage gain calculatedβhelps remember the main points of a mirror.
π― Super Acronyms
VGC - Voltage Gain Constant; helps you recall whatβs essential when calculating amplifier gains.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Current Mirror
Definition:
A circuit configuration that maintains a constant current through one branch by mirroring it to another branch.
-
Term: Collector Current (I_C)
Definition:
The current flowing through the collector terminal of a transistor.
-
Term: Beta (Ξ²)
Definition:
The current gain of a bipolar junction transistor; defined as the ratio of collector current to base current.
-
Term: Voltage Gain
Definition:
The ratio of output voltage to input voltage in an amplifier, often expressed in decibels.
-
Term: Early Voltage
Definition:
An important parameter that characterizes the output characteristics of a transistor; it indicates how the collector current changes with the collector-emitter voltage.
-
Term: Output Resistance
Definition:
The resistance seen by the load connected to the output of an amplifier, which impacts voltage gain.