85.2.4. Active Mirror Load Benefits

This part and if we analyse this circuit it becomes like a common source amplifier, where the load it is diode connected. So, the circuit becomes like this...

In this chunk, we are introduced to a circuit that behaves like a common source amplifier. By analyzing the configuration, you can see that the load behaves as a diode-connected load, which is crucial for certain types of amplification. This setup is useful because it gives rise to specific electrical properties that enhance the amplification process, particularly in small-signal environments.

Think of the circuit like a water pipe system. If you connect a valve (the diode) in one part of the pipe, it can help control and maintain the pressure (voltage) more effectively. Just like that, the diode-connected load helps the circuit maintain better operational characteristics for amplification.

At this point we are giving the small signal along with the DC. Of course, this node it is getting the bias similar to this point and we like to know what will be the corresponding output here due to the small signal...

This part discusses the introduction of small signals alongside a direct current (DC) bias. It explains that the output can be analyzed to determine how the input small signal will affect the output voltage. The voltage outputs are related through their dependence on the gain, specifically under common mode conditions. This relationship between input and output helps us understand how circuits react under small signal conditions.

Imagine you're talking to a friend who is located far away. The background noise (the small signal) plus your voice (DC bias) together determine what your friend actually hears. If you speak louder, they hear the intended message better, like how amplifiers work when applied to small signals.

So, we may say that v under common mode operation is also = v, and that gives us v_common mode. And hence the corresponding common mode gain...

This chunk describes the concept of common mode gain, which is crucial in understanding how well a circuit can reject noise. The common mode gain is calculated based on the characteristics of transistors in the circuit. It becomes crucial because a low common mode gain is generally desirable in amplifier circuits, as it helps reduce noise from common sources.

Think of common mode gain like trying to listen to music while there’s a loud crowd around you. If your headphones have a good noise cancellation feature (low common mode gain), you hear the music clearly and the noise is minimized. This is similar to what we desire in amplifier designs.

To summarize what we can see the advantage of having this current mirror in the load part...

This section summarizes the advantages of employing an active current mirror load. One key point is that it significantly reduces common mode gain, which is beneficial in many amplifier applications. Lower common mode gain implies better common mode rejection, which allows for a clearer signal output and enhanced performance in differentiating between desired and undesired signals.

Imagine trying to pull a heavier suitcase with one hand while holding a cup of coffee with the other. If you had a friend to help with the suitcase (the active current mirror), you'd be able to carry your coffee without spilling it, just as the circuit helps maintain signal integrity while handling amplification.

Since the DC voltage here is the same for the two nodes the DC voltage here it can be directly obtained from this node...

In this segment, we learn about how the DC voltage is managed within the circuit. It highlights the ease of deriving a usable DC bias from the active load configuration. This aspect is critical when discussing the following stages of circuit operation, including how the voltage can effectively be utilized in PMOS transistor biasing.

Imagine setting up a power source for a team of lights in a room. If you establish a consistent voltage (like ensuring the power source is stable), it's as easy as plugging the lights into the same socket to ensure they all work well together. This stable DC voltage helps power the next components in the circuit without interruptions.

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