Then, a larger amount of current flows from the collector to the emitter than from an external circuit into the base. Once the electrons reach the narrow base region, reverse-biasing of the base-collector junction allows the collector to gather electrons from the emitter. Electrons flow from the heavily-doped n+ material to the p-type material and holes move from the p-type material to the n+ region. The construction of a BJT takes us back to pn diodes in that the base-emitter junction of an npn transistor operates as a forward-biased diode.
The middle, narrow section of p-type material (p) l forms the base of the transistor while the other less doped n region (n) forms the collector of the transistor. One n region (n+) of the transistor receives a heavier doping of charge carriers than the other n region and serves as the emitter for the transistor. Taking this an additional step further, an npn transistor has two pn junctions placed back-to-back.
What is a Bipolar Junction Transistor, and What Does It Do?īipolar Junction Transistors-join three layers of p-type and n-type together to construct either pnp or npn transistors. Small signal amplifiers-such as bipolar junction transistors (BJT) work as linear amplifiers. Linear amplifiers produce an amplified output signal that has the exact shape as the input signal. The non-linear amplification produced by our auditory systems gives us the sensitivity that we need when listening to low- and high frequencies. Referring back to the basilar membrane and cochlear, we see a non-linear amplifier because the amplitude of the movement is not proportional when compared to the level of sound pressure. Amplification occurs as the cochlear enlarges the signal by transferring energy to the signal from an external source.Īmplification is a fundamental part of electronic circuit design. While the basilar membrane performs as a frequency analyzer and frequency-tuned delay line, the cochlear mechanically amplifies the movement of the membrane.
As the vibrations vary in frequency, high frequencies produce peaks near the narrow end and low frequencies peak toward the wide end. Each wave travels from the stiff, narrow end to the wider, flexible end, increases in amplitude, and then decreases in amplitude. With one end stiff and narrow and other end wider and flexible, the basilar membrane becomes stimulated by sine waves. In all seriousness though, the basilar membrane -in partnership with the cochlea and tiny hair cells-allows all of us-and all our fellow vertebrates-to hear or perceive sound. If we asked most people about the purpose of the basilar membrane, we might receive answers ranging from something that protects a boat hull from leaking to something about strange lights in the night sky.
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