87.1.2. Department of Electronics and Electrical Communication Engineering

So dear students welcome back after the break. So, before the break we are talking about the numerical examples of the current mirror. As you can see here, we have used Beta-helper to improve the non-ideality factor due to the base current loss. In the next example, we will see the improvisation of the numeric current mirror circuit to take care of the non-ideality factor due to early voltage.

This chunk sets the stage for the discussion on current mirrors, which are essential components in electronics that allow for the copying (mirroring) of currents from one part of a circuit to another. The mention of a 'Beta-helper' refers to a technique used to enhance the performance of these circuits by addressing inherent inefficiencies such as base current loss, which can affect the ideal output of a current mirror.

Think of a current mirror like a relay team in a race. Each runner (or segment of the circuit) needs to pass on the baton (current) effectively. If the handover isn't smooth (due to inefficiencies like base current loss), it slows down the whole team, just like inefficiencies can reduce the overall effectiveness of a current mirror in electronic devices.

To be more precise, we like to place one cascode transistor here that improves the output resistance of the current mirror.

Introducing a cascode transistor is a method to enhance the output resistance of a current mirror circuit. By adding this layer, you effectively isolate the output from variations in the voltage, which helps maintain a more consistent current. This is crucial in precision applications where even small variations can lead to significant errors.

Imagine you have a beautiful plant that needs just the right amount of water to thrive. If the water pressure fluctuates, the plant might end up over or under-watered. Adding a cascode transistor is like placing a pressure regulator on the water line; it ensures the environment around the plant (the output current) remains stable, no matter the fluctuations upstream.

So in the next example, we are starting with MOSFET version, and then after that we will go to the BJT version.

This segment indicates that the lecturer will demonstrate examples using both types of transistors—MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) and BJTs (Bipolar Junction Transistors). Each type has its characteristics, and understanding how current mirrors operate with both allows students to appreciate their versatility in circuit design.

Consider diving into two different types of swimming styles: freestyle (like MOSFETs) and butterfly (like BJTs). Both can help you move through water efficiently, but each requires different techniques. By exploring both styles, you can find out which one suits you best in various situations, just like choosing between MOSFETs and BJTs for different electronic applications.

Now coming to the different sizes of different transistors given here, we do have for transistor-1, we do have the parameter it is 1 mA/V². For transistor-2 and transistor-3, we do have parameters as 4 mA/V². The threshold voltage we are keeping the same for simplicity of the calculation.

In this section, parameters for the transistors are discussed. The transconductance, indicated by mA/V², gives insight into how effectively each transistor can amplify the current. Setting these parameters similarly helps simplify calculations and comparisons between the different configurations and designs.

Think of these parameters like the horsepower ratings of engines in cars. A car with 1-horsepower can do some work, but a car with 4-horsepower can do much more efficiently. Similarly, understanding the specifications of transistors enables engineers to choose the right ‘engine’ for their circuit’s current mirroring tasks.

Now we need to find the value of this V_GS1 and the current flowing here from whatever the voltage 12 V it is given to us...

This part dives into the practical calculations involved in finding the gate-source voltage (V_GS1) and the respective current for the circuit. It emphasizes how precise values must be derived systematically, considering voltage drops and transistor characteristics to ensure correct performance.

Imagine you're baking a cake. To get it just right, you'll need to measure your ingredients accurately and pay attention to the recipe. Similarly, calculating voltages and currents in a circuit requires close attention to the numbers to ensure everything functions together perfectly.

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