![]() ![]() If we were to fall into the linear/active region then the bottom part of your wave gets distorted. Why do we want to be in the middle? Again, because of that nice constant relationship between input voltage and current. Biasing in the middle gives us the most space on either side. When we increase our amplitude of the input wave, the output wave will grow until it either hits the top (your voltage rail) or the bottom (the linear region), whichever is closer. Our output wave comes out with a vertical (DC) offset equivalent to our biasing - it 'rides' on top of the DC. You can get the largest dynamic range out of an amplifier by biasing it to be in the exact middle of the saturation region which is this flat zone along the IV curve of the BJT: A good amplifier (which can be a single BJT and some resistors, look up Common Emitter/Collector/Base Amplfiers, etc) will have a very large dynamic range. This refers to the peak amplitude of the waves that you can put in and get out of the amplifier. In amplifier theory, you specifically design amplifiers to be biased so that they have the largest 'dynamic range'. A BJT can be looked at as two diodes, but it's more complicated than that. To give a slightly different answer on top of what everyone else has already beaten me to: You forward bias a diode by applying a DC voltage greater than or equal to its forward drop voltage. ![]() Different tape materials work better with different amounts of this bias. This bias signal improves the linearity of the magnetization, reducing distortion from the hysteresis of the tape's magnetic particles. ![]() When a signal such as audio is recorded to magnetic tape, this is done with the addition of tape bias: a high frequency AC signal. There are situations in which a signal is added for proper operation, but it is not a simple fixed offset yet, it is still called a bias. If the output of a quiescent amplifier is supposed to be ideally at 0V, but it measures at 25 mV, then we usually say that the amplifier has a "25 mV DC offset", rather than a "25 mV bias". In electronics, a bias is usually deliberate, as in an "offset required for proper operation" it does not have a negative meaning like in "biased sampling" or "biased opinion". If an AC signal rides on a DC signal, we can simply say that it has a DC bias of so many volts, though not always. You could identify a systematic offset in some statistical data. But we digress: the point here is that an offset is called bias, not only in electronics. This allows floating-point numbers, as a whole, to be compared for inequality using purely integer operations. A zero exponent is represented by some middle value like 10000000000, rather than using two's complement, which would create a situation in which there are two sign bits. In floating-point number representations, like IEEE 754, the exponent field is said to be biased. If you have a biased opinion, you are displaced from a neutral position. ![]()
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