What is Biasing: Definition and 45 Discussions

In electronics, biasing is the setting of initial operating conditions (current and voltage) of an active device in an amplifier. Many electronic devices, such as diodes, transistors and vacuum tubes, whose function is processing time-varying (AC) signals, also require a steady (DC) current or voltage at their terminals to operate correctly. This current or voltage is a bias. The AC signal applied to them is superpositioned on this DC bias current or voltage.
The operating point of a device, also known as bias point, quiescent point, or Q-point, is the DC voltage or current at a specified terminal of an active device (a transistor or vacuum tube) with no input signal applied. A bias circuit is a portion of the device's circuit which supplies this steady current or voltage.

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  1. C

    Avalanche relaxation oscillator biasing resistor

    I've tried the circuit in this article. It works very well and I've obtained 2ns clear pulses at 150 V (the main issue was to find the right avalanche voltage, which turned out to be 150-160V for my 2n3904 transistor). While the basic principles of operation in this circuit is clear for me, I...
  2. C

    Biasing a MOSFET with constant-current source

    Homework Statement Hi, I'm just going through amplifier circuits and I'm having some trouble with amplifiers in which the MOSFET is biased by a constant current arrangement. Here's my issue: In the MOSFET saturation equation, if we set ID, we will be able to obtain Vgs. Which means that if...
  3. G

    Engineering Biasing circuit with a MOSFET: am I missing something

    Homework Statement I have the following circuit with MOSFET (cascode amplifier). [![enter image description here][1]][1] [1]: https://i.stack.imgur.com/BAqQh.png Information given: ##V_t=1V## ##I_1=20\mu A## ##k=10 \mu AV^{-2}## Knowing that ##V_b## is 5V determine the minimum value of the...
  4. S

    A Spin-Polarized Edge State Magnetization Biasing

    Some materials, notably graphene and some other 2D nanomaterials, possesses spin-polarized edge states, e.g., where one edge may allow the conduction of spins oriented "up" while the opposite edge only allows conduction of "down" spins. My question is not why these spin-polarized states exist...
  5. G

    How is the circuit above biased for temperature stabilization?

    I have a few questions about the circuit above. 1.This is an ordinary CE amplifier, which uses current mirror to provide temperature stabilization and bias for Q2, right? 2. Like Collector feedback bias and Voltage divider bias, this is just another way of biasing a transistor to provides...
  6. R

    What happens when applying a constant current source to a biased BJT?

    What happens if for argument's sake you have a voltage of 15V and a resistor of 1k connected to the base of a BJT thus biasing it with 15/1000=.015amps and then you apply a constant current source to the emitter/collector that is 1. less than beta*baseCurrent 2. more than beta*baseCurrent 3...
  7. G

    Depletion zone and current in forward-biased PN junction

    Hello. I've learned that in PN junction, forward-biasing on it pushes holes in P-type and electrons in N-type toward the junction so depletion width is reduced. Is it due to that in N-type side(P-type side), pushed electrons (holes) are recombined with holes (electrons) in depletion zone? And...
  8. G

    Depletion zone and current in forward-biased PN junction

    Hello. I've learned that in PN junction, forward-biasing pushes holes in P-type and electrons in N-type forward junctions so depletion width is reduced. Is it due to that in N-type (P-type), pushed electrons (holes) are recombined with holes (electrons) in depletion zone? And what is true...
  9. P

    DC biasing in MOSFET Rectifier

    Hi there, I m a beginner in Analog IC design field. Currently, I have a project which is to design a high sensitivity rectifier by using Synopsys simulator. However, I m stuck in the beginning part which is the DC biasing of MOSFET transistor. The design specification as below: Technology ...
  10. K

    Understanding KVL Loop in BJT Biasing and Calculating Ve: A Guide

    Please help how Ve is calculated what i think is that it should be: -Ve=-Vee+IeRe; How Ve is taken positive please someone draw equivalent circuit for same
  11. thankz

    Thermal runaway in class AB amp biasing

    I was watching this video and I have the question, if using a bjt as a diode what is the difference (thermal characteristics) from a regular diode, I ask this because on-semi makes bjt's with diodes in them specifically for class ab amps, is their any benefit besides less thermal lag?
  12. CKaiL

    Single stage amplifier with current mirror biasing

    Homework Statement Homework Equations ID= kn (Vgs - Vth)^2 The Attempt at a Solution I asked to find the current I D , M2. [/B] I think in order to solve this question I need to find Vgs but how do I do that? RC1 = 2k ohm R = VDD - Vgs / I D ,M2 VDD = 5V , and R = 2k ohm and I have 2...
  13. L

    Engineering Designing a Bias Circuit for BJT with Optimal Ratio and Voltage Drop

    Homework Statement It is required to design the bias circuit as shown in figure for a BJT whose nominal {\beta} is 100. a.) Find the largest ratio {(R_B/R_E)} that will guarantee {I_E} remains within 10% of its nominal value for B as low as 50 and as high as 150. b.) If the resistance ratio...
  14. E

    Why is Biasing Important for Photodetectors?

    Hello I just want to ask why do we bias the photodetector before starting any setup? Thank you
  15. ranju

    Transistor Biasing: Zero Signal Collector Current Explained

    I have studied that "zero signal collector current should be atleast equal to the maximum collector current..." but what is the reason behind this?? and why we need to to consider this zero signal collector current .ultimately what is the significance..if we have to see when we apply the signal...
  16. A

    Biasing: Explained in Electronics

    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?
  17. FOIWATER

    Need help biasing this transistor circuit

    I am having troubles biasing this transistor circuit Mainly, I cannot find Ic The only equation I can come up w/ is 6 - Vce - ie*Re - (-6) = 0 but it doesn't help me, as I do not Vce I do not know how to find Ib, Vs is messing me up, I am not sure how to analyze this... The given...
  18. C

    Understanding Bias in Semiconductor Devices

    Is there not a difference between bias as in "A diode is forward/reverse biased" and establishing the terminal voltages/currents needed to bring say a transistor to the quiescent point? Just curious
  19. C

    Best way of explaining PN Biasing to a friend?

    Hey everyone, got a quick question Last semester, I ended up taking a solid state physics course and surprising myself I ended up getting a B- in the class (most of the other people ended up getting D's). For the most part much of this due to the 'memorize the equation' and 'plug and chug'...
  20. M

    Mosfets Biasing Enhanced-Type Mosfets?

    Simple Question: Do Enhanced-Type Mosfets (And not Depletion Type ones) have Fixed Bias Configuration? If yes how do we draw the transfer curve? And locate Q point? (I didnt seem to find it in the book, only present for Depletion types)
  21. P

    Conduction in reverse biasing too? Is it the case with transistor?

    Conduction in reverse biasing too?? Is it the case with transistor?? I have a mechanical analogy of diode in which a socket is provided with a one way valve. (figure 1st below). The arrow inside the circle shows the direction of motor pump. When there is enough pressure to lift the valve...
  22. T

    Biasing amplifiers and what they do to the input and output voltages

    If we have a input voltage that has a voltage higher then the linear region of the amplifier characteristics graph, what does amplifier biasing exactly do to the wave so there is no clipping, distortion or cut-offs and saturations.
  23. M

    What's the point of biasing any transistor?

    Hi guys. I learned that you need to apply DC biasing to establish your transistor's amplification zone. Some weeks ago I was struggling (as almost we all do with anything related to E.E.) with transistor amplifiers. I had to make 3 amplifiers with 3 different biasing configurations. I...
  24. G

    Does This Circuit Compensate for Temperature-Dependent Changes in VBE?

    I'm trying to convince myself that the circuit below will compensate for temperature-dependent changes in VBE. But I can't seem to figure out what the collector voltage of Q1 is. Even if I assume a base voltage of 0.7V, the base current is still unknown (to me at least) so I can't calculate the...
  25. F

    Pn junction, diode and energy level of conduction band during forward biasing

    Hello Forum, I am looking at the energy levels between the n and p regions of a diode. The p-side has a conduction band that starts at a higher energy (same for the valence band). The n-side has the valence and condution bands that are at lower energy. The Fermi energy line is the same...
  26. A

    BJT Biasing - Simple easy 1 minute answer

    Homework Statement Find IB, IC, IE, VCE, VBC, and VEB for the NPN transistor in the circuit below for β = 50, 150, 500. Let VCC = 10 V, R1 = 100 KΩ, R2 = 400 KΩ, RC=2 KΩ, and RE = 0 Ω. Assume VBE = 0.7V.Homework Equations V = iR IE = Ib + IcThe Attempt at a Solution My question is that if RE...
  27. L

    BJT differential amplifier biasing

    I was looking at input stage of 741 internal ckt - http://en.wikipedia.org/wiki/File:OpAmpTransistorLevel_Colored_Labeled.svg how exactly are the 2 transistors Q1,Q2 biased? I looked at bjt differential input stage wiki here -...
  28. S

    Biasing NMOS using current mirror

    Hi I need a brief explanation on how a Current Mirror is used to Bias an NMOS using Constant Current Model. My Doubts are :- * Where the input is given ? * If the current remains constant how does it work ? * If the current does not remain constant then why say constant current ? Bit...
  29. F

    Understanding biasing and ohms law

    Hello, I am trying to get my head around biasing. I do understand the principles. In the attached circuit the Collector current is 2.5mA and the collector resistor is 1K. Therefore my circuit here is biased at 2.5V. The power supply is 5V. So that would give a 2.5V drop over the collector...
  30. S

    JFET Biasing in Cascode: Designing a High Input Impedance Differential Amp

    Hi, I'm trying to design a simple differential amp with extremely high input impedance. I'm using a couple of JFETs at the input stage to accomplish this. However, because I'm sending the signal from there to a differential amp, I don't want any DC offset, but I'm a little bit confused about how...
  31. J

    Reverse Biasing a Voltage Regulator

    Hello All, Simple question here. I have a microcontroller development board that plugs into the wall and has a garden variety LM7805 type 5V regulator on the board for powering the microcontroller and other peripherals. But also on this board is a header that allows the 5V from the board to...
  32. A

    How can I calculate R1 and R2 values for this transistor biasing circuit?

    Hi guys, I am trying to find a way to calculate biasing network for the attached circuit. Basically I need to find R1 and R2 values for operating point of I0 = 10mA and V0 = 10V and Vs = 16V. DC current gain is assumed to be hFE=80. How do you calculate R1 and R2 based on these info...
  33. L

    Transistor Biasing: Calculating Input & Output Resistance

    Homework Statement See attachment. Homework Equations The Attempt at a Solution Input resistance is R1||R2 I don't know how to calculate output resistance. To calculate the base current, I calculated the voltage at the resistor divider (5V), thevinized the base circuit and...
  34. A

    Transistor Biasing: Common Emitter, Base, Collector

    can anyone please tell me when and why we required different configuration of transistor i.e. common emitter or common base or common collector? advanced thanks.
  35. K

    Voltage Regulators: Understanding Transistors Biasing at 11:35

    hi i can't understand something in voltage regulators http://www.youtube.com/watch?v=9FJJre-HG_0&feature=channel at 11:35 he starts explaning why Vb's equation is like that but i don't get it at 12:00 he says that Vcc/(R1+R2) gives the current through the two resistors but how is that...
  36. B

    What is the role of biasing in a Class A BJT amplifier?

    Can someone clarify the overall purpose and implications of biasing a BJT Class A amplifier? I just can't get my head wrapped around the entire purpose. As far as I know, biasing the circuit will place it in a certain operating region, but I don't know the limits/implications of doing this...
  37. A

    What is the ideal ratio for external resistors in voltage divider biasing?

    I want to know is there any constant or suitable ratio for external two resistors which we use for the base of the BJT in 'voltage divider biasing'? I have heard that the ratio of those two resistors should be something like 3.. but I am not sure...
  38. S

    Transistor Biasing: Calculating Ic, Ib, and Power Dissipation

    Problem Statement: 1. Given that the beta of a transistor is 36, Vcc=5v, Vbb= 3.6V, Rc=440 ohm, Rb=640 ohm, find Ic, and Ib. Also find power dissipated across transistor. Figure: http://yfrog.com/7hdiagram1j Assume silicon diode. [Ie vbe = 0.7] The attempt at a solution I applied voltage...
  39. P

    Biasing: Understanding Input Signal Ranges & Frequency Impact

    I was studing about baising in general (irrespective if it is for BJt or MOS) and just looking at the graph i had several questions. I know the basic concept, the amplifiers, +ve and -ve saturation limits causes the signal outside the limit to truncate. to ensure that the signale should not...
  40. S

    Which Components Are Crucial for Biasing an NPN Transistor?

    Is it the voltage divider and/or the Rc resistor that is responsible for biasing an NPN transistor. I am aware the role each play, but was just wondering which part actually biased the transistor, i wouldve thought both?
  41. H

    IC Biasing with Current Sources

    I understand current sources are used to bias IC circuits, but how does the Ro (Dynamic Output Resistance) of the current source (Either simple, Widlar, or Wilson) effect the amplifier? Why is a higher Ro better than a lower Ro?
  42. N

    Engineering BJT Biasing Circuits: Compare Advantages, Uses & Benefits

    We've base biased circuit, voltage divider, emitter bias, and collector feed back bias...I'm looking for resources, to compare those 4 types, what are the advantages of each type, why is it used, and where... I know BJT's work in amplifiers, but i need more detail concerning those different...
  43. denian

    Engineering Common emitter amplifier circuit using feedback biasing

    i don't have the basic of analog, but i tried to look for in the books. unfortunately, the books are using voltage divider biasing instead of feedback biasing. i have a circuit like this: http://www.mrnerdy.com/forum_img/BJTampfeedbackbiase.jpg would anyone tell me the flow of the current in...
  44. D

    DC biasing using voltage divider

    how do I use a voltage divider to biasing a signal that goes from -5v to 5v so that it goes from 0 to 2.5?
  45. C

    Qn5What is the purpose of using a self-biased circuit for MOSFET amplifiers?

    Hi, I know how to bias a BJT transistor to operate in the active region, so that the amplifier circuit can operate as a small-signal amplifier. Two methods (i) Use biasing resistors to form a self-biasing circuit. (ii) Use diode biasing, coupled with biasing resistors. Qn1 However, how...
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