en>EmausBot: Bot: Migrating 1 interwiki links, now provided by Wikidata on d:Q2162400

2013-06-04T13:56:33Z

Bot: Migrating 1 interwiki links, now provided by Wikidata on d:Q2162400

← Older revision		Revision as of 15:56, 4 June 2013
Line 1:		Line 1:
	~~Emilia Shryock~~ is ~~my title~~ but ~~you~~ can ~~call me anything you like~~. ~~Body building~~ is 1 of the ~~things I adore most~~. ~~South Dakota~~ is ~~exactly where me~~ and ~~my husband live~~. In ~~her professional life she~~ is a ~~payroll clerk but she'~~s ~~always wanted her own company~~.<br><br>~~My web page~~: [http://~~sddch~~.~~org~~/?~~document_srl~~=~~345265 at home std testing~~]		{{about\|biasing in '''electronics'''\|\|Biasing (disambiguation)}}
			'''Biasing''' in [[electronics]] is the method of establishing predetermined [[voltage]]s or [[electric current\|currents]] at various points of an [[electronic circuit]] for the purpose of establishing proper operating conditions in [[electronic component]]s. Many electronic devices whose function is [[signal processing]] time-varying ([[alternating current\|AC]]) [[signal (electrical engineering)\|signals]] also require a steady (DC) current or voltage to operate correctly. The AC signal applied to them is [[superposition principle\|superposed]] on this DC bias current or voltage. Other types of devices, for example magnetic recording heads, require a time-varying (AC) signal as bias. The [[operating point]] of a device, also known as bias point, quiescent point, or Q-point, is the steady-state voltage or current at a specified terminal of an active device (a transistor or vacuum tube) with no input signal applied.

			==Overview==
			In [[electrical engineering]], the term ''bias'' has the following meanings:
			# A systematic deviation of a value from a reference value.
			# The amount by which the average of a [[set (mathematics)\|set]] of values departs from a reference value.
			# [[Electrical force\|Electrical]], mechanical, [[magnetic force\|magnetic]], or other force ([[vector field\|field]]) applied to a device to establish a reference level to operate the device.
			# In [[telegraph]] [[signalling (telecommunication)\|signaling]] systems, the development of a positive or negative [[direct current\|DC]] [[voltage]] at a point on a [[telephone line\|line]] that should remain at a specified [[reference level]], such as zero.

			:''Note:'' A bias may be applied or produced by (i) the electrical characteristics of the line, (ii) the [[terminal equipment]], and (iii) the signaling scheme.<ref>{{FS1037C MS188}}</ref>

			Most often, bias simply refers to a fixed DC voltage applied to the same point in a [[electrical network\|circuit]] as an [[alternating current]] (AC) signal, frequently to select the desired operating response of a semiconductor or other electronic component (forward or reverse bias). For example, a bias [[voltage]] is applied to a [[transistor]] in an [[electronic amplifier]] to allow the transistor to operate in a particular region of its [[transconductance]] curve. For [[vacuum tube]]s, a (much higher) [[grid bias]] [[voltage]] is also often applied to the grid electrodes for precisely the same reason.

			A hot bias can lower the tube life span, but a "cool" bias can induce [[crossover distortion]].

			Bias is also the term used for a high-frequency signal added to the [[sound reproduction\|audio]] signal recorded on [[magnetic tape]]. See [[tape bias]].

			Bias is used in [[direct broadcast satellite]]s such as [[DirecTV]] and [[Dish Network]], the [[integrated receiver/decoder]] (IRD) box actually powers the [[feedhorn]] or [[low-noise block converter]] (LNB) [[receiver (radio)\|receiver]] mounted on the dish arm. This bias is changed from a lower voltage to a higher voltage to select the [[Polarization (waves)\|polarization]] of the LNB, so that it receives signals that are polarized either [[clockwise]] or [[counterclockwise]], thereby allowing it to receive twice as many [[channel (communications)\|channels]].

			We still need to determine the optimal values for the DC biasing in order to choose resistors, etc. This bias point is called the quiescent or Q-point as it gives the values of the voltages when no input signal is applied. To determine the Q-point we need to look at the range of values for which the transistor is in the active region.

			==Importance in linear circuits==
			Linear circuits involving [[transistor]]s typically require specific DC voltages and currents for correct operation, which can be achieved using a biasing circuit. As an example of the need for careful biasing, consider a transistor amplifier. In linear [[amplifier]]s, a small input signal gives larger output signal without any change in shape (low distortion): the input signal causes the output signal to vary up and down about the Q-point in a manner strictly proportional to the input. However, because a transistor is nonlinear, the transistor amplifier only approximates linear operation. For low [[distortion]], the transistor must be biased so the output signal swing does not drive the transistor into a region of extremely nonlinear operation. For a bipolar transistor amplifier, this requirement means that the transistor must stay in the [[bipolar junction transistor#Regions of operation\|active mode]], and avoid cut-off or saturation. The same requirement applies to a [[MOSFET]] amplifier, although the terminology differs a little: the MOSFET must stay in the [[MOSFET#Modes of operation\|active mode]] (or saturation mode), and avoid cut-off or ohmic operation (or triode mode).

			===Bipolar junction transistors===
			For [[bipolar junction transistor]]s the bias point is chosen to keep the transistor operating in the active mode, using a variety of [[bipolar transistor biasing\|circuit techniques]], establishing the Q-point DC voltage and current. A small signal is then applied on top of the Q-point bias voltage, thereby either [[modulation\|modulating]] or switching the current, depending on the purpose of the circuit.

			The quiescent point of operation is typically near the middle of the DC [[load line (electronics)\|load line]]. <!-- reasons to be inserted here later --> The process of obtaining a certain DC collector current at a certain DC collector voltage by setting up the operating point is called biasing.

			After establishing the operating point, when an input signal is applied, the output signal should not move the transistor either to saturation or to cut-off. However, this unwanted shift still might occur, due to the following reasons:

			# Parameters of transistors depend on junction temperature. As junction temperature increases, leakage current due to minority charge carriers (I<sub>CBO</sub>) increases. As I<sub>CBO</sub> increases, I<sub>CEO</sub> also increases, causing an increase in collector current I<sub>C</sub>. This produces heat at the collector junction. This process repeats, and, finally, the Q-point may shift into the saturation region. Sometimes, the excess heat produced at the junction may even burn the transistor. This is known as [[thermal runaway]].
			# When a transistor is replaced by another of the same type, the Q-point may shift, due to changes in parameters of the transistor, such as ''current gain'' (<math>\beta </math>) which varies slightly for each unique transistor.

			To avoid a shift of Q-point, bias-stabilization is necessary. Various [[bipolar transistor biasing\|biasing circuits]] can be used for this purpose.

			==Microphones==
			[[Electret microphone]] elements typically include a [[JFET\|junction field-effect transistor]] as an impedance converter to drive other electronics within a few meters of the microphone. The operating current of this JFET is typically 0.1 to 0.5 mA and is often referred to as bias,<ref>http://www.shure.com/ProAudio/Products/us_pro_ea_phantom</ref> which is different from the [[phantom power]] interface which supplies 48 volts to operate the backplate of a traditional condenser microphone. Electret microphone bias is sometimes supplied on a separate conductor.<ref>IEC Standard 61938</ref>

			== See also ==
			* [[Bipolar junction transistor]]
			* [[Bipolar transistor biasing]]
			* [[MOSFET]]
			* [[Idling current]]
			* [[Small signal model]]
			* [[Tape bias]]

			==References==
			<references/>

			== Sources ==
			*{{cite book \| author=Sedra, Adel; Smith, Kenneth \| title=Microelectronic Circuits \| publisher=Oxford University Press \| year=2004 \| isbn=0-19-514251-9}}
			*{{cite book\| author=P.K. Patil;M.M. Chitnis\|title=Basic Electricity and Semiconductor Devices\|publisher=Phadke Prakashan\|year=2005}}
			*{{cite book\| author=Robert L. Boylestad;Louis Nashelsky\|title=Electronic Devices and Circuit Theory\|publisher=Prentice-Hall Career & Technology\|year=2005}}

			== External links ==
			* [http://www.answers.com/topic/bias-technology?cat=technology#Sci-Tech_Encyclopedia Bias] - from Sci-Tech Encyclopedia

			[[Category:Electronic engineering]]

			[[de:Bias (Elektronik)]]

en>Andrewrehn: /* Network analysis */

2011-05-04T18:35:02Z

Network analysis

New page

Emilia Shryock is my title but you can call me anything you like. Body building is 1 of the things I adore most. South Dakota is exactly where me and my husband live. In her professional life she is a payroll clerk but she's always wanted her own company.<br><br>My web page: [http://sddch.org/?document_srl=345265 at home std testing]

Pipe network analysis - Revision history

en>EmausBot: Bot: Migrating 1 interwiki links, now provided by Wikidata on d:Q2162400

en>Andrewrehn: /* Network analysis */