82.1.1. Comparison of 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 . So, minimum required voltage = V here or transistor-3 plus this voltage.

In this chunk, we explore the essence of a practical circuit design. By comparing two different circuit configurations, we note that one yields a higher output resistance, which is advantageous for circuits where maintaining a constant current is important. However, this increase in resistance comes with a trade-off: the requirement for a higher minimum voltage to operate properly. Specifically, for the circuit with higher resistance, the minimum voltage needed is a combination of the voltage across the transistor and additional voltages within the circuit.

Think of this as the difference between two types of water pumps. One pump can move water with minimal effort (lower voltage) but has limited capacity (lower resistance), while the other can move water more effectively (higher resistance) but requires more energy (higher voltage) to work. Choosing the right pump depends on your needs and the resources available.

So, I can say this is I . And I = I { }

Here we discuss a specific issue emerging from the use of Bipolar Junction Transistors (BJTs) in current mirror applications: the loss of reference current. This loss occurs due to the relationship between the currents in the circuit wherein one value of current supply is diminished when it is shared among multiple transistors (as indicated by the equation). Understanding this loss is crucial in designing efficient circuits since it can affect their overall performance.

Imagine you’re dividing a pizza among friends. If you only have one pizza (the reference current), and you have to share it with several friends (transistors), everyone gets a smaller slice (less current). The more friends you invite, the tinier the slices become, which represents the loss of current in the BJT circuit.

So, 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 a current amplifier which is referred as Beta-helper circuit.

In this segment, we look at a solution to the current loss issue discussed earlier: the introduction of a Beta-helper circuit. By adding an extra transistor, this additional component can amplify the current and help maintain a higher reference current through the circuit. This compensation mechanism enhances the performance of the circuit by reducing the impact of current loss and controlling deviations in current flow.

Think of it like adding a second waiter at a busy restaurant. If one waiter is overwhelmed and can't serve everyone efficiently, by adding another waiter (the Beta-helper), you ensure that everyone gets served promptly, helping to maintain the restaurant's overall satisfaction and performance.

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.

This chunk emphasizes how the addition of a Beta-helper transistor mitigates the reference current loss. The introduction of this element adjusts the relationship between the main currents in the circuit, effectively offering a multiplier effect on the reference current. The equation presented demonstrates how this enhancement is quantified in the circuit design.

Using the previous analogy, think about how having multiple waiters allows for 'tips' (i.e., better service) to circulate quickly among the staff. The more efficient service can be represented by the multiplied effect of the added transistor that helps keep the reference current from diminishing too much.

So, the final expression of this I or I , if I say this is the I and then we do have the application circuit here.

This chunk summarizes the outcome of incorporating the enhancements discussed previously. It draws attention to the final expression for the output current in the circuit which takes into consideration the improvements made through the Beta-helper circuit. Understanding this arrangement is crucial as it showcases the goal of these modifications: to create a more ideal current mirror that performs with greater accuracy.

Consider your school project which requires a group effort. If every member contributes equally (like a well-balanced circuit), the final outcome will be much more impressive; however, if someone doesn’t contribute effectively (lacking the benefit of the Beta-helper), the group effort may suffer, leading to a less stellar result. Enhancing participation results in a stronger project - just like increasing current efficiency in the circuit.

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