Electronics what is bias

You can dope a semiconductor with materials to facilitate an excess of easily displaced electrons, which we refer to as an n-type or negative region. Furthermore, it is also possible to dope a semiconductor to promote an excess of holes to easily absorb those electrons as well, and we refer to this as the p-type or positive region.

Moreover, the positive and negative regions of the diode are also called its anode P and cathode N. However, diode functionality is only possible, of course, when we merge the two types P, N of materials. Also, the merging of these two types of materials forms what we call a p-n junction. Furthermore, the area that exists between the two elements is called the depletion region. Note: Keep in mind that for proper functionality, a diode requires a minimum threshold voltage to surmount the depletion region.

Furthermore, the minimum threshold voltage in most cases for diodes is approximately 0. Also, the reverse-bias voltage will produce a small amount of current through the diode, and it is called leakage current, but typically it is negligible. Lastly, if you apply a significant reverse voltage, it will cause a comprehensive electronic breakdown of the diode, thus allowing the current to flow in the opposite direction through the diode. In general, when diffusion facilitates the subsequent movement of electrons from the n-type region, they begin to fill the holes within the p-type region.

The result of this action forms negative ions within the p-type region, thus leaving behind positive ions in the n-type region.

Overall, the governing control of this action resides in the direction of the electric field. As you might imagine, this results in beneficial electrical behavior depending, of course, on how you apply the voltage, i. Furthermore, with regards to a standard p-n junction diode, there are three biasing conditions and two operating regions.

The three possible types of biasing conditions are as follows:. Forward Bias : This bias condition incorporates the connecting of a positive voltage potential to the P-type material and a negative to the N-type material across the diode, thus decreasing the width of the diode. Reverse Bias : In contrast, this biasing condition involves the connection of a negative voltage potential to the P-type material and a positive to the N-type material across the diode, thus increasing the width of the diode.

Zero Bias : This is a bias condition in which there is no external voltage potential applied to the diode. A reverse bias reinforces the potential barrier and impedes the flow of charge carriers. In contrast, a forward bias weakens the potential barrier, thus allowing current to flow more easily across the junction. While in forward biasing, we connect the positive terminal of the voltage supply to the anode and the negative terminal to the cathode. In contrast, while in reverse bias, we connect the positive terminal of the voltage supply to the cathode, and the negative terminal to the anode.

A forward bias reduces the strength of the potential barrier of the electric field across the potential, whereas a reverse bias strengthens the potential barrier. A forward bias has an anode voltage that is larger than the cathode voltage. In contrast, a reverse bias has a cathode voltage that is larger than the anode voltage. A forward bias has a substantial forward current, while a reverse bias has a minimal forward current. The depletion layer of a diode is substantially thinner while in forward bias and much thicker when in reverse bias.

Forward bias decreases a diode's resistance, and reverse bias increases a diode's resistance. This reaction to temperature is undesirable because it affects amplifier gain the number of times of amplification and could result in distortion, as you will see later in this discussion.

A better method of biasing is obtained by inserting the bias resistor directly between the base and collector, as shown in figure below. By tying the collector to the base in this manner, feedback voltage can be fed from the collector to the base to develop forward bias.

This arrangement is called self-bias. Now, if an increase of temperature causes an increase in collector current, the collector voltage V C will fall because of the increase of voltage produced across the load resistor R L. This drop in V C will be fed back to the base and will result in a decrease in the base current.

The decrease in base current will oppose the original increase in collector current and tend to stabilize it. The exact opposite effect is produced when the collector current decreases. Self-bias has two small drawbacks: 1 It is only partially effective and, therefore, is only used where moderate changes in ambient temperature are expected; 2 it reduces amplification since the signal on the collector also affects the base voltage.

This is because the collector and base signals for this particular amplifier configuration are degrees out of phase opposite in polarity and the part of the collector signal that is fed back to the base cancels some of the input signal. This process of returning a part of the output back to its input is known as degeneration or negative feedback. Sometimes degeneration is desired to prevent amplitude distortion an output signal that fails to follow the input exactly and self-bias may be used for this purpose.

A zero exponent is represented by some middle value like , rather than using two's complement, which would create a situation in which there are two sign bits. This allows floating-point numbers, as a whole, to be compared for inequality using purely integer operations. But we digress: the point here is that an offset is called bias , not only in electronics.

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". An unwanted offset is just an "offset". 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".

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.

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. This bias signal improves the linearity of the magnetization, reducing distortion from the hysteresis of the tape's magnetic particles.

Different tape materials work better with different amounts of this bias. 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.

A BJT can be looked at as two diodes, but it's more complicated than that. In amplifier theory, you specifically design amplifiers to be biased so that they have the largest 'dynamic range'. This refers to the peak amplitude of the waves that you can put in and get out of the amplifier.

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:. Our output wave comes out with a vertical DC offset equivalent to our biasing -- it 'rides' on top of the DC.

This gives us our dynamic range. 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. Biasing in the middle gives us the most space on either side. Why do we want to be in the middle? Again, because of that nice constant relationship between input voltage and current.

So back to the diode: If we were to bias it to only 0. So if we bias a 0. Forward or reverse biased usually applies to diodes. A forward biased diode has a higher voltage at its anode than its cathode. If this is higher than the small threshold it conducts in that direction. A reverse biased diode has a higher voltage at its cathode than its anode, and will not conduct unless you exceed the breakdown voltage and destroy it.

Biasing in an audio context usually refers to an arrangement to keep the middle of a signal in the centre range of an amplifier. This gives the best use of the output range of the amplifier.