68.1.15. Transition to Common Source Amplifier

So, in the next slide what we can do we are going to draw the small signal equivalent circuit, but to calculate the gain we need to remember these parameters particularly small signal parameters values.

This section introduces the idea of the common source amplifier and highlights the need to focus on the small signal equivalent circuit parameters when calculating the gain. It sets the stage for understanding how the common source amplifier operates in small signal conditions.

Think of a common source amplifier like a public speech where the speaker (amplifier) needs to project their voice (signal). The microphone captures the speaker's voice (input), and an amplifier enhances it so that the audience (load) can hear it clearly. The small signal parameters are like key features of the microphone setup that affect how well the voice gets amplified.

So, here we do have the circuit it is for our reference it is shown here and the corresponding small signal equivalent circuit it is drawn at this at this place.

The excerpt indicates that a small signal model is being used, which simplifies the analysis of the circuit by considering how small variations in input affect output. This model is crucial for understanding the amplifier behavior when the input signal is much smaller than the bias point.

Imagine you’re trying to measure small vibrations in a bridge while a large truck is driving over it. Instead of measuring the effect of the truck, you focus on the tiny vibrations caused by lighter cars. This is akin to using a small signal model to understand how minor inputs impact the overall system.

Now, since we are ignoring source resistance here so, we can say that v incidentally equals to v assuming that this capacitor it is successfully bypassing the signal to the base of transistor-1.

This part explains that by ignoring the source resistance, the input voltage can be directly equated with the signal voltage present at the base of transistor-1. This assumption simplifies calculations and allows focus on the amplifier function without interruptions from resistance effects.

Imagine a clear pathway for a stream (signal) flowing into a reservoir (amplifier). If there were obstacles (resistances) blocking the stream, it could lead to inaccurate readings of how much water is flowing in. By ensuring there are no obstructions, we can accurately measure how incoming water levels are amplified in the reservoir.

So, if we consider this is 12 V. So, total here it is 6 V, DC here and then if we consider this is 12 V.

In this chunk, the output voltage swing is discussed, emphasizing how the DC voltage affects the maximum and minimum output voltages that can be achieved. This is important for understanding how the amplifier can handle varying signals without distortion.

Think of a swing set; the position where you attach the swing (DC voltage) determines how high the swing can go (output voltage swing). If the attachment point is too low (low DC voltage), the swing won't reach high altitudes, just as a low DC voltage limits an amplifier's ability to produce higher output voltages.

So, this is matching with that yeah. So, this is 9.63 nF and from this information 5.93 nF and then this ok. In case if we have some source resistance then we can calculate the cutoff frequency coming from the C.

This section discusses the calculated values of input capacitance and how they affect the cutoff frequency of the amplifier. The higher capacitance can introduce a lower cutoff frequency, affecting the frequency response of the amplifier.

Consider a water pipe; if the pipe narrows (high capacitance), it restricts the flow of water (signal) and reduces the maximum allowable flow rate (frequency response). A wider pipe allows more flow; similarly, an amplifier with lower capacitance can support a wider frequency range.

So, if I say that the frequency response particularly higher side if you see. So, gain it is very decent and then it is having 3 dB bandwidth.

This chunk summarizes the performance of amplifiers with active and passive loads, noting their differences in gain and bandwidth. By comparing the two, students can appreciate the advantages of active load configurations over passive ones.

Comparing the two types of amplifiers is like comparing two types of racecars: one designed for speed (active load) that may not handle turns as well (bandwidth) and another designed to be well-rounded but slower (passive load). Each has its own strengths and weaknesses depending on the race conditions.

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