69.1. Analog Electronic Circuits

We are talking about CE amplifier with active load and passive load. We discussed and compared their performance. Before we go to CS amplifier, we must make a note of the CE amplifier and the circuit we have discussed particularly its stability issue of its operating point.

This chunk introduces the concept of Common Emitter (CE) amplifiers with both active and passive loads, emphasizing their performance comparison. The speaker highlights the importance of understanding the CE amplifier, particularly focusing on the stability of its operating point before moving on to the Common Source (CS) amplifier.

Think of a CE amplifier like a car engine. Just as the engine's performance can vary based on the fuel type (active vs. passive load), the amplifier's behavior changes according to its load. Before understanding a new engine (CS amplifier), it's crucial to know how the existing engine (CE amplifier) runs under different conditions.

Suppose, we do have seen this circuit what we have discussed before. And in case say the early voltage of the two transistors they are not consistent with whatever we have planned and or in case if there is any variation of one of these two bias resistors or maybe β of the 2 transistors if they are changing either with time or whatever it is may be due to temperature or due to aging effect that it will directly affect the operating point here.

This section discusses how variations in key parameters of transistors, such as early voltage and beta (β), can impact the operating point of the CE amplifier. For instance, if β decreases due to aging or temperature changes, the output voltage will also shift away from its ideal value, leading to performance issues.

Consider a group of friends planning to meet at a restaurant. If one person arrives late (shifting the operating point) due to traffic (temperature changes), the rest of the group might become frustrated (output voltage changes) as they wait longer (performance issues). Just as timing matters for the friends’ meeting, consistent parameters are crucial for the amplifier's performance.

So, let you imagine a case that is suppose all the things are same, but then suppose this early voltage it got changed from say it 100 to maybe 200. Then this voltage if this is getting changed to 200. Then ( V ) = 1 + (V of transistor-2 divided by its early voltage). ... The problem it will be even more severe particularly, if β is getting changed and rest of the things are remaining same.

This chunk elaborates on how a change in the early voltage affects the output voltage of the CE amplifier. If the early voltage increases, it changes the relationship between the output voltages of the two transistors in the circuit. Particularly, the discussion emphasizes how variations in transistor parameters like β can further compound these issues, leading to instability in the amplifier's performance.

Imagine adjusting the settings on a thermostat. If you increase the temperature setting (early voltage), it changes the entire heating system's output (output voltage). However, if the thermostat is faulty (i.e., a change in β), even slight modifications can lead to significant fluctuations in room temperature, similar to how variations affect amplifier operation.

To have a solution we like to have a stable bias and here we do have the corresponding circuit. If we compare the previous circuit and this circuit, this R instead of connecting to ground, we are connecting to this output node as a result it is making a negative feedback ensuring that the output DC voltage it is not so sensitive to process parameter.

In this section, a solution to stabilize the amplifier is presented by changing the connection of the bias resistor. By connecting it to the output node and introducing negative feedback, the circuit becomes less sensitive to variations in transistor parameters, thereby enhancing stability.

Think of this stability approach like adjusting the sails of a sailboat in changing winds. Instead of letting the wind dictate your path (parameter fluctuations), you adjust the sails (negative feedback) to maintain a steady course (stable output). This way, even if winds change direction (parameter variations), you can still navigate smoothly.

Suppose, this β is getting changed to 180 and let you assume that rest of the things are same, namely; V and V are remaining same as whatever you have planned ... output signal swing towards the negative it is almost close to 0.

This chunk explains how a reduction in β affects the current and output voltage in the circuit. If β decreases while other parameters remain constant, it implies that the operating point may shift closer to saturation, which can lead to a reduced output swing. An emphasis is placed on understanding these dynamics to troubleshoot potential performance issues.

Consider an orchestra where instruments (transistors) are supposed to play together (maintain their parameters). If one instrument plays softer (lower β), the overall music (output voltage) may lose volume, distorting the intended harmony (signal swing). Just like in music, balance among components is essential for optimal performance.

This arrangement it is having some feedback mechanism which is helping us to maintain this voltage remaining towards its middle point. But of course, at the beginning we have to make some sensible calculation and sensible you know selection of the value of the resistances.

Here, the speaker talks about the integral role of feedback mechanisms that ensure the output voltage stays stable despite variations in parameters. The need for careful calculation and resistance selection is stressed to make sure the design is both effective and efficient.

Think of this feedback mechanism like a thermostat in a home heating system. The thermostat monitors the room temperature (output voltage) and adjusts the heating accordingly. If temperatures drop, it kicks in the heater to bring them back to the desired level (middle point). This feedback helps maintain a comfortable living environment, much like how feedback in the circuit maintains stable operation.

--