57.1. Analog Electronic Circuits

So, dear students welcome back after the break. So we are talking about composite transistor. And what we said is that if we have amplifier particularly multi configuration amplifiers where two transistors are having different configuration or maybe the same configuration. Then the analysis can be done slightly smarter way.

In this introductory section, the professor explains the concept of composite transistors in multi-configurational amplifiers. A composite transistor combines two transistors, which may have different or similar configurations. This innovative approach is aimed at simplifying the analysis of amplifier circuits.

Think of a composite transistor like a team of two people working together. Each person (transistor) has their own strengths, and when combined, they can tackle more complex tasks more efficiently than if they were working alone.

And to do that what you can do two transistors together we can consider a single one say for example, you do have Q and Q together. Where Q it is its collector is connected to supply V . And its emitter it is directly connected to transistor-2 and then at the emitter will may or may not be having this bias current.

Here, the professor explains how to connect two transistors (Q1 and Q2) in a composite structure. The collector of Q1 connects to the power supply, while its emitter connects directly to the base of Q2. This configuration allows both transistors to work together in a unified circuit, simplifying the design.

Imagine a relay team where the first runner (Q1) hands off a baton (the signal) to the second runner (Q2) to complete a race. In this analogy, the offset connection represents the transfer of responsibility or signal from one runner to the next.

So, the moment you make this composite structure in CC configuration then what will be we getting how CC followed by CC configuration we can get. So, likewise if the composite structure or composite transistor if you connect in CE configuration, then we can get CC followed by CE configuration.

In this part, the professor describes different configurations that can arise from composite transistors: common collector (CC) and common emitter (CE). By altering their connectivity, students can derive multiple amplifier configurations, each with unique properties, enabling versatile applications in amplifier circuits.

Think of different paths in a relay race, where each path represents a configuration. Just as runners choose different routes for efficiency, engineers select amplifier configurations based on the circuit's requirements.

So, we can connect maybe a bias current here or maybe a resistor and let you call this is output since this is CC configuration the collector may be connected to supply directly.

The professor discusses the flexible design within the CC configuration, allowing connections for bias currents and output. The circuit can adjust based on specific component requirements, showcasing the adaptability of composite transistors in practice.

Consider building with LEGO blocks. Just as you can rearrange LEGO pieces to create different structures, engineers can modify circuit connections to fit desired performance outcomes in a composite transistor circuit.

First thing we need small signal parameter. So, what are the small signal parameter? So, β of the transistor then r collector to emitter resistance. Then trans conductance and then base to emitter resistor resistance r .

The section introduces small-signal parameters essential for analyzing transistors in circuits. Parameters like beta (β), collector-emitter resistance, transconductance, and base-emitter resistance help predict the transistor’s behavior under small voltage variations, critical in amplifier design.

Just as an athlete’s performance can be quantified through metrics like speed and strength, the small-signal parameters offer engineers key performance measures for transistors in circuits.

Then we can find the expression of each of this parameter in terms of the internal and then parameters of the internal or constituent transistor namely Q and Q.

In this segment, the professor stresses the importance of deriving expressions for composite transistor parameters based on the constituent transistors Q1 and Q2. Such calculations are vital for understanding how changes in one component affect overall amplifier performance.

Think of a recipe where the final dish's flavor depends heavily on each individual ingredient. Similarly, the performance of a composite transistor relies on the characteristics of each constituent transistor.

In fact, this is very much of course, with a minus sign here I sorry I forgot that there is no surprise if you see this circuit the primarily what we obtain the voltage gain we are getting from the second stage the coming from the Q.

The discussion pivots to analyzing the voltage gain from composite circuits. The professor notes that the gain typically stems from the second transistor in a configuration and that it's integral in determining the amplifier's functional output.

Imagine a water pipe system where the water pressure increases as it passes through a series of valves (transistors). Each valve adds to the system's overall force (voltage gain), affecting how much water can be pushed through at once.

Now, let us move to MOS Tran MOS based circuit in fact, sorry before we go to the MOS circuit we do have one more information to we like to share.

In concluding the lecture, the focus shifts to moist based circuits after discussing composite transistors. The introduction of this topic highlights the transition between varying amplifier technologies, emphasizing the continuous evolution in circuit design.

Just as a chef eventually transitions from one dish to another in a diverse menu, engineers constantly shift their focus between technologies to enhance their circuit designs based on their varying needs.

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