84.1. Analog Electronic Circuits

So, dear students welcome back after the break. So, before the break we are talking about usage of current mirror for CE amplifier, and also CS amplifier. Now we also can see that usage of current mirror for Common Collector amplifier as well.

In this chunk, we return to the topic of current mirrors in amplifiers. After discussing their use in CE (Common Emitter) and CS (Common Source) amplifiers, we will expand our focus to the Common Collector amplifier. This indicates a variety of applications for current mirrors across different amplifier configurations, emphasizing their versatility in analog electronic circuits.

Think of current mirrors as a method of distributing power in a network. Just like water can be divided into two pipes of different widths to provide flow to various parts of a garden, current mirrors help in managing the flow of electrical current to support different amplifier setups.

So, here we do have the transistor level circuit transistor-1 it is the main amplifying transistor input port is here. And then the output port it is here and earlier what we said is that the current of this transistor it can be set by one reference current.

In this section, we discuss the layout of the circuit focusing on transistor-1, which serves as the main amplifying component. The input and output ports are identified here, and the significance of a reference current is introduced. This reference current is crucial because it determines the operation of the amplifying transistor, allowing for stable and predictable function.

Imagine a chef preparing a recipe. The reference current is like a key ingredient that ensures the dish tastes right. Without the correct amount of that ingredient, the final dish could vary widely, just as the transistor's current would deviate without an appropriate reference.

So, we do have this R and based on the value of this R we can get a current here and we call this is I the reference current.

The bias resistor R plays a critical role in setting the reference current I for the transistor. By adjusting the value of R, we can control how much current flows through the transistor, which is vital for maintaining optimal performance in the circuit. This relationship highlights the importance of resistor selection in circuit design.

You can think of the bias resistor as the throttle in a car. Just as the throttle controls the amount of fuel that flows to the engine, thus controlling the speed of the car, the resistor controls the current to the transistor, ensuring it operates effectively.

So, this is the exact equation assuming transistor-2 and transistor-3 they are identical and then this may be well approximated by × IREF.

Here we derive an equation for the collector current of transistor-2 based on the assumption that it is identical to transistor-3. This approximation allows for simplification in calculations, which is a fundamental concept in circuit analysis. Understanding how to manipulate and utilize these equations is key for diagnosing and optimizing amplifier performance.

This is akin to simplifying complex math problems: if two variables are equal, we can treat them as one, reducing computation time and effort. This makes it easier for engineers to design and troubleshoot circuits.

So, similar to common collector amplifier the current mirror can also be used for common drain amplifier which is the MOSFET counterpart of this circuit.

In this chunk, the applicability of current mirrors extends to common drain amplifiers (the MOSFET equivalent of common collector amplifiers). This connection further showcases how current mirrors are essential across various transistor technologies in constructing reliable and effective amplifiers.

Imagine using the same recipe book (current mirror) for two different types of meals (amplifiers); although the meals may require slight adjustments, the fundamental method is the same. This highlights how versatile the current mirror approach is within different amplifier contexts.

So, of course, since both the resistors are very high you can well approximate this by 1. Now, next thing is that the current mirror can also be used our rather frequently used for differential amplifier.

This section transitions to exploring the use of current mirrors in differential amplifiers, setting the stage for discussing how they can enhance circuit performance. The approximation of high resistors simplifies analysis, enabling clearer focus on the advantages brought by current mirrors in this context.

Imagine enhancing a sports team by bringing in versatile players who can adjust to different positions based on the game needs. Current mirrors make differential amplifiers more adaptable, allowing for improved performance across varying scenarios.

In fact, there are different possible applications and the applications of the current mirror on differential amplifier it is having 3 folds.

In this section, we discuss the multiple benefits that current mirrors bring to differential amplifiers, one of which includes enhancing the common mode gain. This concept is critical as it directly links to the amplifier's ability to reject noise anddistortions, showcasing the practical superiority of their implementation.

Think of a noisy room. A good discussion group (differential amplifier) should drown out the noise (common mode signals). By using current mirrors (filters), the group can focus more effectively on their conversation, reducing the impact of the disturbances around them.

So, now if you replace the load part by active current mirror then what will be getting is the improvement of common mode and differential mode gain.

This segment highlights how replacing passive loads with active devices, such as current mirrors, results in enhanced performance of differential amplifiers. This transformation can dramatically improve both the common mode and differential mode gains, leading to a better overall circuit performance.

This is akin to upgrading from manual gears to automatic gears in a vehicle; the car (differential amplifier) becomes more efficient and responsive to changes (gains), elevating the overall driving experience.

So, we do obtain the current here in terms of I. Likewise, here also we can get the current relationship namely I′ it becomes I × by dropping ( ) part.

In the final chunks, we summarize the current relationships established through previous equations. Understanding these relationships forms a basis for evaluating how modifications to the transistor arrangement can improve circuit operations. This level of comprehension allows engineers to make informed design choices.

Consider a weaving pattern in a fabric. Each thread (current) needs to connect properly to create a cohesive fabric (circuit). By understanding and manipulating these intersections, we can create stronger and more complex structures, much like engineered circuits.

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