68.1.8. Signal Swing Analysis

So, if the DC voltage here it is 6 V if the DC voltage here it is 6 V, how much is the signal swing we can expect? From positive from this equation point towards the positive side the voltage at the collector it can go as close as the supply voltage in fact, supply voltage ‒ V saturation.

In this part, the concept of signal swing is introduced, which pertains to the range of voltage that an amplifier can output in response to an input signal. When the DC voltage at the collector is 6 V, the maximum output voltage can approach the supply voltage, with a small reduction for saturation voltage. This saturation voltage (V_sat) is the minimum voltage the output can reach before the transistor stops conducting. The swing can be calculated using the formula: maximum collector voltage = supply voltage - V_sat.

Think of an amplifier like a swing in a playground. The height of the swing you can reach (the signal swing) is like how high the output voltage can go above the resting position (DC voltage). Just like the swing can't go higher than the top bar (supply voltage), the output voltage can't exceed the supply voltage minus whatever limits the swing, like a safety bracket (saturation voltage).

And we can assume that V of both the transistor around say 0.3 V of transistor-2 CE(sat) and saturation it = 0.3 V typically that is what it can be taken 0.3 V. So, we do have a 6 V, DC here and then if we consider this is 12 V. So, total here it is 6 V ‒ 0.3.

The maximum positive output swing can be determined by subtracting the saturation voltage (V_CE(sat), which is typically around 0.3 V) from the DC voltage. Here, it is shown that with a DC voltage of 6 V, the total positive swing can be calculated by subtracting 0.3 V, which leads to a maximum output voltage of 11.7 V (i.e., 12 V - 6 V - 0.3 V). This result indicates how far above the DC operating point the signal can swing in the positive direction.

Imagine you're going up a hill while riding a bike. Your starting point is like the DC voltage (6 V), but you can only go higher until a fence stops you (saturation). The fence is placed at a certain height (0.3 V), so you can only go slightly higher than your starting point before hitting the fence. Therefore, your total height limit is less than your initial elevation.

So, likewise ‒ve side we can say that here we do have 6 V it can go as low as ground + 0.3.

In determining the maximum negative swing, the minimum output voltage can be derived by allowing the output to drop to just above ground (0 V), accounting for the saturation voltage. Since the DC voltage is 6 V, it can go as low as 5.7 V (i.e., 6 V - 0.3 V), before it reaches the point where the transistor would turn off and not conduct.

Picture arriving at sea level while navigating a boat. Your boat can only dip so low into the water (like stretching the output negative), which is close to the shoreline (0 V), but can't go totally underwater or it will sink (turn off). Hence, your lowest point, while still afloat, is just above sea level.

So, output swing wise we can say it is ± 5.7 V, which means that the voltage here it can go as high as with respect to 6 V here. It can go as high as 11.7 V, likewise lower side it can go as low as 0.3 V so, that is the good swing.

To summarize the signal swing analysis, the output voltage can vary from 0.3 V to 11.7 V. This means the total expected output swing is ±5.7 V around the nominal DC operating point of 6 V, which indicates a healthy operational range for the amplifier. This analysis helps in understanding how well an amplifier can handle varying input signals without distortion.

Imagine your favorite tuning fork. When struck, it resonates between two extremes - high and low tones, just like the output voltage can swing between two values. The range of sound it can produce contains this balance between the highest and lowest pitch. A greater range of swing indicates a more versatile tuning fork or in this case, a better amplifier.

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