What is the Midband Gain of a Transistor?

Midband Gain of a Transistor

The Midband Gain of a transistor is the transistor's gain at its mid frequencies; the midband gain is where the transistor's gain is at the highest and most constant level in its bandwidth.

When analyzing the gain of a transistor, the frequency of the input AC signal that the transistor receives is key to how much amplification the signal will receive from the transistor. A transistor does not have a constant gain for all frequencies in its bandwidth. For very low frequencies, the transistor amplifies the signal very little, as can be seen in the graph above. As the frequency rises, the gain of the signal gradually goes up and up. When the signal reaches the mid-frequencies, the gain of the transistor (called the midband gain) is at its most constant and highest level. After, as the frequency increases, the bandwidth reaches the high frequency region, where the gain again falls. As the frequency gets higher from this point, the transistor's gain continues to fall until it no longer amplifies the signal at all.

The midband gain is the most important region of transistor amplification. This is because this is the region of frequencies where a transistor produces a constant and high level of gain. When a transistor is rated for its gain or amplification factor, it is the midband region that this is referring to.

To learn how to calculate the midband gain of a transistor, see How to Calculate the Midband Gain of a Transistor Circuit.

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