82.1. Introduction to Current Mirrors and Practical Circuits

Now, this is this is I should say more practical circuit. Now if I compare the 2 circuits, definitely I am getting higher resistance in this case. But the only drawback here it is the minimum required voltage to get this benefit it is higher namely, for this case we require one V or rather V .

In this chunk, we are talking about the practicality of a certain circuit configuration, specifically a current mirror. It is mentioned that by comparing two circuit designs, one offers higher resistance, which is generally desirable. However, the downside is that this improved performance requires a higher minimum voltage, noted as V_CE(sat). Essentially, while higher resistance can improve the circuit's ability to maintain a constant current, it comes at the cost of needing a higher voltage to operate effectively.

Imagine a water pipeline. A pipeline designed to carry water more effectively (higher resistance) might need a stronger pump (higher voltage) to push water through, as opposed to a simpler design that works with a weaker pump.

So, minimum required voltage = V_CE(sat) here or transistor-3 plus this voltage. And in fact, that voltage if I go through this loop, it can be shown that this voltage and this voltage they are equal. So, that is one V_BE(on). Whereas for this simple current mirror, the minimum required voltage here it was only V_CE(sat).

This chunk delves deeper into the requirements for operating a current mirror. It specifies that the minimum voltage needed includes the saturation voltage of a specific transistor (transistor-3) plus an additional base-emitter voltage (V_BE(on)). This means that the effective voltage required to ensure the circuit works correctly can vary significantly based on the configuration used.

Think of this like the energy required to lift weights. If you have a heavier weight (transistor-3), you need more energy (voltage) not only to lift it but also a bit more to ensure you can hold it (the extra base-emitter voltage).

So, that is how we can increase the output resistance and we can get the less dependency of the output current on the output voltage.

The focus of this chunk is on increasing output resistance, a crucial aspect of current mirrors. Higher output resistance in current mirrors means that variations in the output voltage will have a lesser effect on the output current. This characteristic is vital in applications where stable current is necessary, suggesting that good design can effectively isolate output current from voltage variations.

Consider a sturdy table that can hold a lot of weight (high output resistance) without wobbling or collapsing, even if someone bumps into the table (change in voltage). You want something stable that doesn’t easily get affected by external forces.

To avoid this loss or to reduce this loss, what we can do? We can place one transistor here, we can place one transistor here, which may work as current amplifier which is referred as Beta-helper circuit.

This chunk introduces the Beta-helper circuit, which is a technique to reduce the loss of current in the current mirror configuration. This is done by introducing an additional transistor that helps amplify the current, ensuring that the reference current is better utilized and thereby improving the overall performance of the circuit. The term 'Beta' refers to the current gain of the transistor.

Imagine having a friend who can help you lift heavier boxes. Alone, you struggle with the weight, but with your friend (the extra transistor), you can lift more effortlessly. This teamwork translates into increased efficiency in carrying items (or currents, in electronics).

So, we can say that by adding this extra transistor, the loss of this current loss of this reference current; if I say that is the loss, then that is getting reduced by this factor. As a result, the relationship between I_ref and I becomes I = I_ref { (1 + β) }.

Here, the equation is detailed which shows how the addition of the Beta-helper transistor improves the relationship between the reference current (I_ref) and the output current (I). By including this transistor, the output current can be significantly increased by a factor of (1 + β), where β is the current gain of the added transistor. This means a more efficient and stronger output current in the current mirror circuit.

Think about how using a booster can amplify sound from a guitar. The sound initially produced is your reference (I_ref), and with a booster (Beta-helper), the sound increases significantly (I), allowing it to fill a large auditorium.

In summary, what are the things we have discussed in this lecture, we have started with motivation of going for current mirror namely, to implement current biasing element in amplifier...

In the conclusion of the section, the benefits of current mirrors are reiterated, emphasizing their role in implementing current biasing in amplifiers, their signal mirroring capabilities, and how advancements like the cascade structure and the Beta-helper circuit enhance their performance. This summation ties all the previously discussed concepts back together, enhancing understanding.

Imagine a well-made recipe (the lecture) that covers all the essential ingredients (current mirror principles) and techniques (improvements). By reviewing how each ingredient works together, we can better appreciate the beauty of the final dish (the effective current mirror).

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