# Meaning of bias

1. Jan 9, 2014

### aaaa202

In an exercise I am doing the term biased is mentioned in the context that the voltage source is biased. Now english is not my mother tongue (and even so I don't know if it's a common word). What does biasing mean in electronics?

2. Jan 9, 2014

### tiny-tim

hi aaaa202!
yes, bias is a common word, but it has several meanings, and the relevant meaning is perhaps the least common

a coin is biased if, instead of coming up equally heads and tails, it systematically comes up more heads (or more tails)

i think the adoption of the word by electricians is by analogy with that: the voltage is biased in the sense that it is systematically different from what you'd expect it to be

(the more common meaning is that a person is biased if he favours one side rather than another, in an argument, or politics, or a game, etc)

for a good description of the meaning in electronics, see http://en.wikipedia.org/wiki/Biasing#Overview

3. Jan 9, 2014

### Staff: Mentor

tiny-tim's wiki source is a reasonable reference, although it contains several lesser-used meanings of the word bias, and may be a bit hard to translate in some places.

Can you show us the exact quote and context for what you wrote "voltage source is biased"? That is a strange combination of words, IMO. You can use a voltage source to provide bias to a circuit, but it makes no sense to say that a voltage source is biased...

4. Jan 9, 2014

### Loren

Bias means that a voltage (positive or negative) is applied to a "node" in the circuit to offset or alter the node's voltage or the output of that circuit.

For example, I have a tube amplifier where a bias of negative 54 volts DC is applied to the grid or input pin of the output tube. This forces the tube to operate in its linear region when an AC voltage (the audio signal) is applied to the same grid pin.

On an op amp you may bias one of the input pins to offset the output of the op amp. For example, you may want the output to swing from -5VDC to +5VDC when the input swings from 0VDC to 2VDC. A bias applied on the other input pin will offset the output to do that.

Keep in mind that all voltages must be referenced from some point.

By the way, your English seems very good!