64.1.4. Lecture – 64

Before I going to the next topic I must see here that this calculation of the C I did a small mistake hear, it should be 135 because C = C + in in π C (1 + 204) and so, here we do have 5 and also here we do have 10. So, I miss this 10 µ part. So, 10 + 1025. So, that gives us 1035 pF capacitance.

In this chunk, the speaker reflects on a mistake made in the previous calculation of the capacitance C, which should have been 135. The corrected formula includes C in parallel with another capacitor with a factor of (1 + 204). The finalized value of the capacitance is calculated to be 1035 pF, factoring in previously omitted values.

Imagine a student double-checking their math homework and realizing they missed a number. Correcting this error is crucial to ensure the final answer is accurate, similar to how engineers need precise calculations to ensure circuits function correctly.

The advantage of cascode amplifier with respect to standard CE amplifier and namely what you have seen is that in case if you are retaining this passive element for both the cases, then gain wise we do not get much advantage.

The cascode amplifier offers significant benefits compared to standard Common Emitter (CE) amplifiers. While keeping the passive elements, the gain difference is minimal. However, it's highlighted that the cascode amplifier excels in providing an extended bandwidth and higher gains under certain conditions, particularly when the source resistance is high.

Think of the cascode amplifier like a two-story tower. While each floor individually might not seem much stronger, stacking them allows for a total height advantage that enables you to see further. In electronics, the 'height' refers to the gain while the extended bandwidth represents a wider view of frequencies.

Now it may be a situation where this resistance it may be small or whatever the cutoff frequency we are obtaining by this R and then C and R that may be beyond the upper cutoff frequency defined by R and the C.

This chunk discusses scenarios where load resistance may vary. If this resistance is smaller than expected, it might affect the cutoff frequency, which is the frequency beyond which gain declines. This context is crucial for understanding how these values interplay in determining the amplifier’s performance.

Consider this like tuning a radio. If the station's frequency is not matched correctly (like having an improper load resistance), you may either hear static (no performance) or just a weak signal (diminished gain). Proper adjustments ensure clear sound.

In fact, cascode amplifier it is having two types of advantages; one is extending the bandwidth as we just now we have discussed particularly in presence of significantly large value of the source resistance, the other advantage which is commonly used is that the increasing the gain drastically.

This section elaborates on how cascode amplifiers take advantage of situations with high source resistance. Notably, these amplifiers help widen the operational bandwidth while simultaneously amplifying the gain significantly. These traits make the cascode amplifier a powerful tool in electronics.

Imagine a highway with two lanes. A wider road can allow more cars (data) to travel simultaneously, increasing flow without congestion. Similarly, the cascode amplifier lets more signal throughput while boosting strength (gain) effectively.

So, to demonstrate that in the next slide what we are going to do we will be getting almost the same numerical problem except we do have a change here. Particularly, if you see the value of this R instead of 2.8 k now we are going to take a big value say 10 MΩ.

Here, the lecturer sets up a numerical problem that will illustrate the cascode amplifier's capabilities under different resistive loads. Changing the resistance value from 2.8 kΩ to 10 MΩ is key to demonstrating significant gains due to the cascode setup.

Think of adjusting the size of a funnel to pour a liquid. A larger funnel allows you to pour more liquid at once—just like increasing resistance allows the cascode amplifier to handle larger signal gains without issues.

So, what you are expecting from the lower side as we have discussed based on the resistance here based on the R and R, the current flow here quiescent current flow here it is 2 mA, the voltage here it is 0.6 V DC the voltage here it is 1.2 V.

This chunk explains the expected current and voltage flows within the amplifier circuit. The quiescent current—2 mA—indicates the standard operational state of the circuit. The voltages at various points highlight the expected DC conditions under operation, setting the stage for analyzing output and performance.

Think of this as measurements taken inside a working factory. Knowing how much product is being produced (current) and how much inventory is available (voltage) helps in assessing the efficiency and adjustments that might need to be made.

If I consider this resistance here it is g r r. If I ignore say or if I consider this node it is connected to ground. So, if I calculate this value of course, for DC we cannot say this is ground, but for the time being let we tolerate such kind of things.

The lecturer delves into calculating the input impedance and voltage at different points in the circuit. They discuss how certain resistances when connected to a reference point (ground) significantly affect outcomes but must be viewed within the context of the entire circuit operation.

Consider a complex plumbing system where certain pipes (resistances) affect water flow (current). Understanding how each segment interacts with the whole system helps identify where adjustments can improve overall performance.

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