84.1.5. Active Load Current Mirror

So, dear students welcome back after the break. So, before the break we were talking about the usage of current mirror for CE amplifier, and also CS amplifier. Now we also can see that usage of current mirror for Common Collector amplifier as well. So, here we do have the transistor level circuit transistor-1 it is the main amplifying transistor input port is here.

This chunk introduces the concept of current mirrors being used in different types of amplifiers, specifically mentioning CE (Common Emitter), CS (Common Source), and Common Collector configurations. It sets the stage for discussing how a current mirror can enhance the performance of these amplifiers by providing a controlled reference current. Understanding different amplifier types is crucial as they each have unique applications in electronic circuits.

Think of a current mirror like a water faucet. If you want a specific amount of water (current) flowing to a plant (amplifier), you set the faucet to allow that much water. Similarly, a current mirror helps set the flow of electrical current to maintain consistent performance in electronic devices, making them operate smoothly.

And then the output port it is here and earlier what we said is that the current of this transistor it can be set by one reference current. So, instead of having reference current this is what we do have the implementation of the current source. In fact, if you see that it consists of a bias resistor R maybe you can see bias.

This chunk discusses the importance of setting a reference current for the operation of the amplifier. In electronic circuits, the reference current is crucial for determining how much current flows through the main amplifying transistor, allowing for consistent behavior. The current source is associated with a bias resistor, which helps in generating this reference current, ensuring stability in the amplifier's performance.

Imagine a railway system where the train (current) runs on a track (circuit). The speed of the train needs to be regulated to ensure safe travel. The reference current sets a limit on how fast the train can go, much like the bias resistor ensures the amplifier operates at the optimal current level.

We can say that the collector current of transistor-2 I it is well approximated by × I . So, this is the exact equation assuming transistor-2 and transistor-3 they are identical and then this may be well approximated by × I.

Here, the construction of the current mirror is discussed, particularly focusing on transistors-2 and-3, which are ideally identical. The relationship between the collector current of transistor-2 and the reference current in transistor-3 is mathematically established. This principle is vital for ensuring that the current mirror can accurately reflect the currents and maintain the same characteristics for both transistors.

Consider two identical twins: one has a specific talent (current) and we expect the other to have the same talent. Similarly, in a current mirror, when one transistor (twin) has a certain amount of current flowing, we rely on the other identical transistor to mirror that exact behavior.

Once we get the DC operating point then to find the gain from input to primary output we can draw the small signal equivalent circuit and since the current mirror here it is not carrying any signal. So, the equivalent circuit small signal equivalent circuit coming out of the current mirror it is only r of transistor-2.

This section explains how to find the voltage gain of the amplifier using its small signal equivalent circuit once the DC operating point is established. It highlights that because the current mirror doesn't carry audio or varying signals, the equivalent circuit simplifies significantly. This step is essential for calculating the performance metrics of the amplifier, particularly the gain.

Imagine a librarian processing books reading them (analog signals) to determine their importance (gain). However, if a section is strictly for storage (the current mirror), the librarian only needs to note down where the books are, simplifying the organization of the information without altering it.

So, similar to common collector amplifier the current mirror can also be used for common drain amplifier which is the MOSFET counterpart of this circuit.

This chunk addresses the application of current mirrors in different types of amplifiers, specifically mentioning the Common Drain amplifier (analogous to Common Collector but using MOSFET technology). This emphasizes the versatility of current mirrors in both bipolar and MOSFET circuits, showcasing their essential role in analog design.

Think of a universal adapter for different devices. Just as a universal adapter can facilitate charging for various types of electronics regardless of brand or model, a current mirror serves multiple amplifier configurations in electronics, ensuring they function optimally.

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