Bias - Page 1
Forum section: electronics / beginners

author: r00n
author_rank: Contributor
timestamp: December 05, 2023, 08:03:09 pm
content: They say that there is no such thing as a stupid question, but this one may be.Why in the English language in the subject of Electronics is the act of simply applying a DC voltage across a component to get it operational termed "Biasing"? Wikipedia definition informs that unlike other homonyms this is not a bad thing. My guess is that parallel circuit containing the component becomes "biased", compared to other sections of the circuit.

author: Benta
author_rank: Super Contributor
timestamp: December 05, 2023, 08:37:39 pm
content: What else would you call it? Offsetting? That's a different thing.Is this some kind of politically correct language thing?

author: TimFox
author_rank: Super Contributor
timestamp: December 05, 2023, 08:39:20 pm
content: In this context, "biasing" means to establish a "quiescent" operating point, about which the voltage and current will vary when an input signal drives the circuit.Historically, with vacuum tubes, one could use a "bias battery" in series with the grid circuit, so that the grid-cathode voltage would vary around the "bias voltage".Or, one could use a suitable circuit in series with the cathode to get the same effect.The words "bias", "discrimination", etc. have developed unfortunate connotations in political rhetoric due to "prejudicial discrimination" in legal or social situations, as opposed to recognition of a difference ("discrimination of right from wrong").

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 05, 2023, 08:49:25 pm
content: I guess if you think of it as biascurrentinstead ofvoltageit makes a bit more sense language wise.Zero bias would be zero idle current in an amplifier or transistor.Like most biases, it depends on "who" you're dealing with... What's a major turn on for a NPN transistor will be a major turn off for the PNP... Kind of like politics and sex

author: TimFox
author_rank: Super Contributor
timestamp: December 05, 2023, 08:54:22 pm
content: It is very frequent to apply a "bias voltage" to obtain a "bias current" value (such as the zero-signal cathode current in the vacuum tube amplifier).In my personal usage, I prefer applying a "bias" voltage to obtain a "quiescent" current, but that is equivalent.The important distinction is between "bias voltage" and "signal voltage", the difference between a constant and a small variation about the constant.

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 06, 2023, 10:38:41 am
content: So do you know what do they call in other languages?

author: r00n
author_rank: Contributor
timestamp: December 06, 2023, 08:25:27 pm
content: Quote from: Kim Christensen on December 05, 2023, 08:49:25 pmLOL - very clever.

author: TimFox
author_rank: Super Contributor
timestamp: December 06, 2023, 10:35:29 pm
content: Next time that you wear a necktie: note that tie fabric is always cut on the bias.

author: tooki
author_rank: Super Contributor
timestamp: December 07, 2023, 06:06:41 pm
content: Quote from: Benta on December 05, 2023, 08:37:39 pmWell, one could probably borrow a word from mechanical engineering and it “pretensioning” (akin to the German “vorspannen”, which IIRC is actually also used to mean biasing in electronics)Quote from: Benta on December 05, 2023, 08:37:39 pmProbably, from someone who’s not aware of the numerous other uses of “bias” (both the noun and the verb) and only knows the one that happens to be politically charged.

author: tooki
author_rank: Super Contributor
timestamp: December 07, 2023, 06:08:51 pm
content: Quote from: TimFox on December 05, 2023, 08:54:22 pmWhile I get where you’re coming from, in my mind “quiescent” has the connotation of being a parasitic characteristic, while “bias” is something done very deliberately.

author: TimFox
author_rank: Super Contributor
timestamp: December 07, 2023, 06:34:42 pm
content: Quote from: tooki on December 07, 2023, 06:08:51 pmI assume the term for the zero-signal cathode current, etc., comes from "quiet".The Google-search definitions vary slightly depending on the context: amplifier, logic gate, voltage regulator, etc. depending on if the "input" or the "load" is zero.I suppose the quiescent current of a three-terminal regulator can be considered "parasitic", and you can't adjust (bias) it.Typical discussion of quiescent current in an amplifier:"When people talk about "biasing" an amplifier, they are referring to setting the "idle", or quiescent, current in the power output tubes.All tubes must be biased, both preamp and output tubes, but it is not always clear whether or not the bias needs to be adjusted when changing tubes."Here, "bias" refers to the voltage applied to the grid-cathode, either an adjustable voltage to the output tubes (called "fixed bias") or automatically by a cathode resistor ("cathode bias") on a power or signal-level tube.Solid-state class-AB amplifiers have similar bias/quiescent current considerations.Some class-B tube amplifiers can use "zero bias", depending on the actual tube characteristics (cathode current at zero grid-cathode voltage).In my physics education, this is analogous to a simple harmonic oscillator formed by a vertical spring holding a weight, where the constant gravitational force on the weight biases the quiescent point away from where the spring would hang absent the gravitational field, and the oscillation is then about that level.

author: wasedadoc
author_rank: Super Contributor
timestamp: December 08, 2023, 01:28:17 am
content: The word "bias" is also used for the high frequency current also applied to the recording head in analogue tape recorders.