89.2. Numerical Examples on Current Mirror and its applications (Part-D)

So here we do have the differential amplifier and the load of course, it is active load, but internally we do have current mirror. So, what we are expecting here is transistor-7 DC wise it will be mirroring its own DC current into transistor-8 and that is good. In fact, we want this current to be the same as this one from a balance point of view. So, we do not have to put any external circuit to bias here.

In this chunk, the narrator introduces a current mirror configuration used in a differential amplifier. The key point here is that transistor-7 copies (or mirrors) its direct current (DC) into transistor-8. This mirroring is crucial for maintaining balance in the circuit, allowing both transistors to share the same electrical current without the need for additional biasing circuits. This design simplifies the circuit and enhances performance reliability by ensuring equal current flow, which stabilizes amplifier operation.

Think of a current mirror like a twin system where each twin (transistor) mirrors the other's behavior. If one twin eats a certain amount of food (sends a current), the other twin automatically mirrors this and eats the same amount, ensuring they stay balanced without needing someone to actively monitor and adjust what each eats.

Again the value of this resistor is 11.4 k, so that makes this current = 1 mA. So, the current flow here is also 1 mA and if we are applying meaningful input common mode DC then half of the current is flowing here and remaining half is here. So, each one of them is 0.5 mA so this 0.5 mA is getting mirrored here.

This chunk focuses on current calculations within the differential amplifier circuit. The narrator explains that the resistor value contributes to a total current of 1 mA. When the input is applied, this current splits evenly between two paths, yielding 0.5 mA for each path. This split current is then mirrored by the current mirror system, ensuring that both transistors maintain the same current level essential for the amplifier's functionality. Understanding this division of current is key to appreciating how the current mirror operates effectively.

Imagine balancing a scale with weights. If you place 1 kg on one side, and want both sides to be balanced, you take half a kg to each side to ensure they both carry the same weight. Here, the current behaves similarly—each half must mirror its counterpart to keep the circuit 'balanced' for optimal performance.

If you ignore this early voltage to calculate the nominal quiescent current, namely ( ) if you consider it ≈ 1 for DC condition. Then the circuit analysis becomes really simple and also we like to say that since this is transistor-7, it is diode connected.

This chunk discusses simplifying calculations by ignoring specific factors in the analysis of the circuit. By assuming a standard early voltage for transistor-7, the differential amplifier's behavior can be easily predicted. The term 'diode connected' means that the transistor's base and collector are shorted, making it function like a diode and influencing the voltage present in the circuit. This concept is essential for understanding how voltage levels are maintained within the overall arrangement of the amplifier, as well as the role of each transistor.

Think about using a light bulb that can glow brightly or dimly depending on how much power it receives. By simplifying the circuit analysis (i.e., ignoring certain complexities), you can focus on understanding how to turn on and off the light reliably without delving into all the intricate details of every wiring, similar to focusing on the primary function of the light rather than each individual electrical path.

We need to find differential mode gain and common mode gain...the voltage coming here v predominantly will be defined by and whatever the signal current is flowing through this.

In this part, the narrator explains the process of calculating differential and common mode gains. The differential mode gain tells how effectively the amplifier responds to the difference in voltage between its two inputs, while the common mode gain assesses how the amplifier handles voltages that are common to both inputs. To find these gains, the circuit's small signal model is referenced, which focuses on how changes in input voltage affect output voltage. Understanding these gains helps predict the amplifier's performance in real-world applications.

Imagine a stereo system where you want to hear only one track clearly (differential mode) while ignoring any noise from both speakers playing at the same time (common mode). The differential gain focuses on loudness differences between tracks, while common gain looks at the general background noise's effect on the sound quality.

So, here we do have this resistor; it is practically 200 k, ... these two are having current mirror so; obviously, then you can find what will be the current flow here.

This closing chunk summarizes the key calculations conducted within the circuit analysis, detailing the use of resistors, current flow estimates, and adjustments needed to find accurate gain values. The emphasis is placed back on the calculations and how to practically derive relevant figures while applying the principles of mirroring current accurately across differential amplifiers. By consistently applying the principles discussed in prior chunks, a logical and coherent series of calculations can be derived, aiding in an efficient understanding of the current mirror and its functions.

When cooking a recipe, you measure ingredients meticulously to ensure everything turns out just right. Each calculation we discussed is similar—each 'ingredient' (i.e., resistor value or current) contributes to the overall mix, determining how well the amplifier 'cooks up' or produces accurate signal outputs.

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