67.5.2. Current Equality Conditions in Circuit Design

Now naturally, then who defines this current? For proper operation, we require both the current should be equal and we need to satisfy some condition to ensure that I and I ; I rather I they should be equal.

In a circuit where two current sources are connected, a fundamental condition must be met for the circuit to operate correctly: the currents flowing through these sources must be equal. This is crucial because any difference in current can lead to one device entering a non-optimal operating region, affecting overall performance.

Imagine two people trying to fill a tank with water from two hoses. If one hose flows faster than the other, the tank will fill unevenly, and one person might end up working harder with little result. Similarly, in electronics, if the currents are not balanced, it can lead to inefficiencies or even damage the components.

Well, at this node we do not have any other circuit connected. So, it is very natural to say that why do we require any condition for this two current to be equal; because it is KCL as we do not have any other circuit connected here.

The requirement for equal currents stems from Kirchhoff's Current Law (KCL), which states that the sum of currents entering a junction must equal the sum of currents leaving the junction. In this case, if no other circuit is connected and only these two currents are present, they must equal each other to satisfy KCL. Additionally, for the active devices to function properly, both must remain within the saturation region, ensuring consistent performance and linearity in amplification.

Think of a roundabout at a busy intersection. For traffic to flow smoothly, cars from different directions (currents) must yield to each other and merge evenly. If one lane has too much traffic while another is nearly empty, it can create accidents or jammed lanes, just like imbalanced currents can cause issues in electronic circuits.

Now naturally, then who defines this current? ... in saturation region whatever the current we do have they are equal.

Each transistor in the circuit defines its current based on its gate-source voltage and respective characteristics. For proper functioning, it is important that both transistors remain in the saturation region—a state where the transistor operates most effectively with its output current determined largely by its input voltage. This condition ensures that the defined currents through the transistors are equal and predictable.

Consider a factory where two machines must work in tandem to produce a product. If both machines receive even power and run smoothly (saturation), the output will be maximal. However, if one machine falters or receives less power, it will slow down the production, similar to how mismanaged transistor currents can impede signal amplification.

If you are not paying good attention and if you are simply saying that I do not have any other circuit connected and the current of the two devices they must be equal. Then what it may happen ... and it will be having a huge consequence on the gain.

If one of the transistors enters a different operational state, say the triode region due to a mismatch in current, this can severely impact the gain of the amplifier circuit. The gain may be lower than expected because one device won't amplify effectively while the other operates optimally, leading to poor signal fidelity.

Imagine a seesaw with kids of unequal weights. If one child is much heavier, the seesaw will tip, and the lighter child won’t have much fun or participate as expected. This situation mirrors how unequal currents affect the functioning of transistors, leading to diminished overall circuit performance.

So, I must make you aware that we have to pay additional attention. So, that the both the devices are in saturation region and of course, their current should be equal.

Ensuring that both devices remain in the saturation region is essential for the designed operational conditions. This not only means monitoring the input voltages but also taking care of the environmental conditions and current settings to keep both devices balanced.

Consider a relay race where each runner has specific laps to complete. If one runner starts problems (like tripping) while another runs perfectly, the team’s overall performance suffers. Similarly, in circuits, if one transistor falls out of its ideal operating region, it could slow down the signal amplification, affecting overall operation.

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