63.6. Voltage Gain Analysis

So, what is the voltage gain? So, try to remember these values of the small signal parameters to get the voltage gain.

Voltage gain (A) is a measure of how much an amplifier boosts the input signal. It is defined as the ratio of the output voltage (v_out) to the input voltage (v_in) of the amplifier. In this context, you should recall the small signal parameters that were determined earlier to calculate the voltage gain.

Think of voltage gain like a microphone amplifying your voice. If you speak into the microphone at a soft volume (input), and the sound recorded by the microphone is loud (output), then the microphone has a high gain because it made your voice much louder.

Now this is the gain from the base terminal or transistor-1 till the output point. Now if I consider this R = 1.3 k. Why did I take 1.33 k? Just for simplicity that, the input resistance here in this circuit calls R which is (r and r it is 1.3 k)

When calculating the overall gain of the circuit, the gain from the base terminal of transistor-1 to the output refers to how much the input at this point is amplified at the output. The choice of R = 1.3 kΩ simplifies calculations since it represents the combined effect of input resistances.

Imagine turning the volume knob on your stereo. If the input (your music source) has a certain loudness and you turn it up a small amount (gain), you'll observe a significant increase in loudness coming from the speakers. Here, the resistors play a similar role in determining how much 'turning up' happens.

So, overall gain A defined as the primary output divided by primary input.

The overall gain A can be calculated by taking the output voltage and dividing it by the input voltage. This gives a clear picture of how much the amplifier enhances the signal. It often takes into consideration multiple factors, including the different resistances and gain contributions from various parts of the circuit.

Think of it as a performance. If a singer usually sings at a volume of 80 decibels (dB) and with an amplifier it reaches 100 dB, then the overall gain is 100/80 = 1.25, meaning the sound is 25% louder. Here, the calculations also factor in the overall effect of different elements in the circuit similar to how the musician's vocal quality or electronics contribute to the total sound.

So, C_in, input capacitance of this entire circuit looking at the base of transistor-1 which, is equal to C and C. And then C of course, it is bridging the base and the collector terminal of transistor-1.

The input capacitance (C_in) affects how quickly the amplifier can respond to changes in the input signal. It is determined by the capacitances associated with the transistors and any external capacitors. When these capacitors are combined, they form an effective capacitance that influences the amplifier’s frequency response.

Think of the input capacitance like a sponge soaking up water. The larger the sponge (capacitance), the more water (signal) it can hold. This means that if the sponge is too filled, it takes longer for it to absorb additional water. Similarly, if the input capacitance is too high, the circuit may not respond quickly enough to changes in the input signal.

The reason is that the gain of this cascode amplifier you may recall if I consider R and then the overall gain, it was.

The configuration of the cascode amplifier affects its performance benefits, including the voltage gain and bandwidth. By comparing it to a simple common emitter amplifier, certain configurations can provide better performance characteristics, despite seeming similar in gain values.

Imagine two types of teams playing basketball: a well-coordinated team (cascode amplifier) that can pass quickly and efficiently compared to a less coordinated one (common emitter amplifier). Even if both teams score the same number of points (gain), the well-coordinated team might perform better under pressure (bandwidth), due to their strategies.

So, to summarize that, if I compare the common emitter amplifier and then cascode amplifier; we can say that, for both the circuits the gain it is very close to each other.

In conclusion, while both the common emitter and cascode amplifiers have similar gains, the cascode design offers advantages in terms of input capacitance and bandwidth. This makes it more suitable for high-frequency applications where quick response to changes in voltage is critical.

Think of the cascode amplifier like a sports car that accelerates smoothly (higher bandwidth), while a regular car (common emitter) might not respond as fast when you hit the gas pedal. Even if both might reach a similar top speed (gain), the way they get there and handle roads can differ drastically.

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