43.3.3. Configuration Discussion

So, you can you can you can do yourself. Now, what we are saying is that what are the necessities or necessary features of the buffer particularly if the circuit is in voltage mode what we just now said that, output resistance of this buffer this resistance should be as small as possible quote and unquote low.

In voltage mode buffers, it's crucial to optimize several resistance characteristics for effective performance. The output resistance must be minimized, meaning it should be as low as possible to ensure that it doesn't affect the voltage levels being passed through the circuit. A low output resistance allows for better performance as it reduces the loading effect on the subsequent stages, ensuring that the amplified voltage remains close to the expected value.

Think of this like a water pipe system. If the output pipe (representing the buffer's output resistance) is very narrow (high resistance), it restricts water flow. On the other hand, if it's wide (low resistance), water can flow freely, ensuring that the water pressure (voltage) at the output remains high and unaffected by the weight of the water in a connected pipe.

So, on the other hand the input resistance of this buffer should be as high as possible. So, quote and unquote high and then input capacitance again it should be as small as possible. So, that the cutoff frequency should not get upper cutoff frequency should not get affected.

For a voltage mode buffer, the input resistance should be made as high as possible. A high input resistance prevents the buffer from drawing too much current from the previous stage, thereby maintaining the signal's integrity. Additionally, the input capacitance must be minimized because large capacitive loads can adversely affect the upper cutoff frequency of the circuit. An increase in capacitance can lead to unwanted filtering of the high-frequency components of the signal, which is detrimental in many applications.

Imagine a sponge (the buffer) placed in a water tank (the previous circuit stage). If the sponge has a high resistance (it's very absorbent), it won't drain the water out too quickly (preserving signal integrity). Conversely, if the sponge were very small (a low capacitance), it wouldn’t hold too much water (preventing signal distortion) and would instead quickly release it, enabling effective transmission without attenuation.

And, then the voltage gain of this circuit preferably it should not be very small. So, we should be rather happy if it is in the order of 1 ok.

For optimal performance of a voltage mode buffer, the voltage gain should ideally be around 1. This means that the output voltage should match the input voltage without significant amplification or attenuation. A gain of 1 is preferable because it allows the buffer to act effectively in isolating stages without altering the voltage levels, which is critical in precision applications where signal integrity must be maintained.

Think of a telephone line that connects two people. If person A's voice (the input) is transmitted perfectly to person B (the output) without getting louder or quieter, we have a gain of 1. However, if A's voice becomes weaker (attenuated) when reaching B, then it’s not functioning effectively. The goal is to keep the communication clear and unaltered, similar to maintaining a voltage gain of 1 in a buffer.

Now, this kind of requirement it is essentially it will be obtained by different circuit configuration namely; common collector if it is implemented by BJT. If it is implemented by MOS transistor it will be common drain; which means that this buffer particularly for voltage mode amplifier cascading this buffer it will be implemented by common collector or common drains stage.

In the context of current mode amplifiers, different configurations are adopted to satisfy the required characteristics. When using BJTs, a common collector configuration is preferred, while for MOS transistors, the common drain configuration is utilized. These configurations help meet specific requirements such as high output resistance and low input resistance, facilitating the correct propagation of current without significant loading effects, and maintaining the fidelity of the signal across different stages of amplification.

Imagine a relay race where runners are passing the baton (representing the signal). Each runner (circuit stage) is set up in a way that allows them to receive and pass quickly and efficiently. A common collector or common drain configuration ensures that when one runner hands off the baton, they do not hinder the next runner's speed, allowing for a smooth transition.

So, what we have we are going to conclude now it is that the common emitter amplifier we have seen it is having some limitation particularly whenever we are cascading and the its not only its gain, but it is not only its gain it is the bandwidth is also getting affected.

To conclude the discussion on buffers, it is emphasized that common emitter amplifiers may suffer from limitations, especially when cascading multiple stages. Both the gain and bandwidth can be affected negatively without intervening buffers. Introducing appropriate buffers with the correct configuration can help in maintaining the desired bandwidth and proper gain across cascaded stages, thus improving overall circuit performance and efficiency.

Think of an assembly line in a factory. If one worker (amplifier stage) is unable to keep up due to constraints (limitations), it slows down the entire process. Introducing buffer zones between the workers ensures that the flow of work continues smoothly, optimizing both the productivity (gain) and efficiency (bandwidth) of the operation.

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