Amplifier Definition and 560 Threads

An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a power gain greater than one.An amplifier can either be a separate piece of equipment or an electrical circuit contained within another device. Amplification is fundamental to modern electronics, and amplifiers are widely used in almost all electronic equipment. Amplifiers can be categorized in different ways. One is by the frequency of the electronic signal being amplified. For example, audio amplifiers amplify signals in the audio (sound) range of less than 20 kHz, RF amplifiers amplify frequencies in the radio frequency range between 20 kHz and 300 GHz, and servo amplifiers and instrumentation amplifiers may work with very low frequencies down to direct current. Amplifiers can also be categorized by their physical placement in the signal chain; a preamplifier may precede other signal processing stages, for example. The first practical electrical device which could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. Today most amplifiers use transistors.

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  1. S

    Why is frequency response an important characteristic of an amplifier?

    Why is frequency response an important characteristic of an amplifier? in this situation we are using a transistor and had to calculate gain using specified frequencies and the resulting voltages through our circuit. My understanding of contemporary electronics is not as strong as i...
  2. jegues

    BJT Differential Pair Amplifier Design

    Homework Statement See first figure attached. Homework Equations The Attempt at a Solution See 2nd figure attached for my work so far at attempting the design. The last figure is what my textbook gives as the small signal analysis of a BJT differential amplifier with emitter...
  3. Femme_physics

    Operational Amplifier Output Voltage with Equal Resistors

    Homework Statement http://img51.imageshack.us/img51/1912/vout.jpg Given the supply voltages of the operational amplifier are (plus and minus)15V, as well it is given that R1 = R2 = R3. We get that Vout is -15V True or false? Explain.The Attempt at a Solution [SIZE="5"]False because it...
  4. Z

    What is a lock-in amplifier with a forcing grid ?

    What is a "lock-in amplifier with a forcing grid"? The context of the title is in an undergrad paper, concerning plasma waves in an glow discharge column. The paragraph which mentioned this is in the section of the paper, Suggestions for Further Research: The most important step remaining...
  5. L

    Operation amplifier - inverting amplifier

    operation amplifier -- inverting amplifier Homework Statement Please refer my attachment which is inverting operational amplifier. Iin = (Vin - VA)/Ri If = ( VA - Vout) / Rf My question is why not Iin = (VA - Vin)/Ri If = ( Vout - VA) / Rf Thanks in advance revered members...
  6. B

    Suggested waveform Amplifier for electromagnetoc coil testing?

    Hi everyone, I am currently doing some experimentation with electromagnetic coils, I realize I will need a waveform amplifier for the testing using my rsr32 function generator. Could someone point me in the direction of a decently priced one?
  7. D

    Finding output voltage of common-drain amplifier

    Homework Statement Hi, I have a basic MOS common-drain amplifier as described below: - Drain connected to 5 V DC - Gate connected to an AC source on top of a 3 V DC source - Source connected to a 200 uA current source with a resistor R connected in parallel. The parallel connection goes...
  8. N

    Understanding a Push-pull amplifier schematic.

    Hi, I'm trying to understand the operation of the schematic I attach. http://imageshack.us/photo/my-images/853/abampschematic.png/ What's the point of having the input at the Q1 collector? I can understand the more common structure shown in wikipedia (...
  9. C

    Current measurement with Lock-In Amplifier SR830

    I have two current signals from a two color Si-photodiode/PbS-photodetector. I want to measure the signal with the Stanford Research Lock-In Amplifier 830. I read in the manual that I can measure currents with the SR830. Does anyone have experience with this? Do I get better signals if I...
  10. P

    Finding Input/Output Impedance of a CE Amplifier: Practical Methods

    how can i find input and output impedance of a ce amplifier- (voltage divider )..suggest practical methods?
  11. S

    Operational amplifier exam questions

    Homework Statement See attached file for relevant questions. I'm finding the Op-amp questions in section A very difficult. Any help with these questions would be much apprietiated. Homework Equations The Attempt at a Solution
  12. Y

    Common source MOSFET amplifier: voltage gain

    Hi everyone, I need to find the voltage gain for the following scheme: My book says I need to calculate 'id' first, which is: id = gm.ro.vin/(Rs+RL+ro+(gm.ro.Rs)) Then with the help of vout = -RL.id you get: Av = -gm.ro.RL/(Rs+RL+ro+(gm.ro.Rs)) So I get the last part, but I really have...
  13. B

    Transistor Amplifier: Quick Question -Vee Equivalent & Parameters

    I have a quick question. I can't find anywhere the answer in my textbook. What is this -Vee in attached image? And how do you equivalent that? And it says here in given parameters that -Vee=-12 V, isn't that +12 V?
  14. G

    Questions about bjt amplifier circuit

    hi all i have some questions about a commen emmiter bjt amplifier circuit . if i had this circuit : and i want to find the ripple of voltage in outout : i will use this equation : V_{O(p-p)}=2I_{CQ} (R_L || R_C) but why i put R_L || R_C not R_L || R_C + R_E or how i conclude that...
  15. S

    Power Amplifier output to 3 Phase Motor

    Hello Everyone, I have a question about how power amplifiers output their power to 3 phase motors. I am using a copley xtl power amplifier to power a 3 phase motor, i want to use a relay to interrupt that motor current but I am not sure how to size it. If the peak output of the amplifier is...
  16. R

    Single Supply Summing Amplifier

    Hi everyone, I'm going to comment about something that happened to me today using Summing OpAmps. First, I simulated the attached circuit in a Project Board. It's supposed to be a Single Supply summing op amp with unity gain. The thing is it never worked. The signals didnt even appear in the...
  17. E

    How can I accurately measure high resistances using a lock-in amplifier?

    Dear all, I measured some very nice data, but it's difficult to analyze, but I try to get out of it what I can. I have diverging resistance and did measure with standard lock-teqnique: apply 0.45V over preresistor and send current over sample and measure the two-probe resistance over the same...
  18. D

    A question related to Operational Amplifier.

    Hello. I believe there's a flaw in my understanding of the operational amplifier. I'm getting a bizarre result that I'd really appreciate if anyone can help me with. :) 1. http://tinyurl.com/6e9ovvp The part I'm having problem with is Q9 (b) (iv). 2. V=IR The Attempt at a...
  19. P

    How Does the AD208 Iso-Amp Function in High Voltage Applications?

    How to use the instrumentation amplifier? Is it a voltage follower? Can it be used for isolation?
  20. B

    Pulse Height Of Pulse Amplifier

    Homework Statement I have attached the question as a photo. It contains two parts. Homework Equations The Attempt at a Solution For part A, is it simply Q=CV where C is given and Q is the elementary charge times 10^6? For B, I am not quite sure where to begin. Any...
  21. T

    Non Inverting Operational Amplifier

    Homework Statement Derive an expression for the gain Vout/Vin. Express your answer in the form of A+jB. Homework Equations The Attempt at a Solution If C is the capacitor in series with R1, gain = 1 + R2/[R1 + 1/(jwC)]. It says to express it in the form of A (real)+ jB (imaginary), but I'm...
  22. T

    Cascode C-S Amplifier (Find Poles in Frequency Response)

    Homework Statement Heres the question, I honestly don't know where to even begin :( An AC model of a cascode common-source amplifier is shown below. M1 and M2 are biased in saturation mode. The parasitic capacitors in the transistors are included. Determine the poles in frequency response...
  23. F

    Understanding the Potentiometer Configuration in an Instrumentation Amplifier

    Problem: http://img443.imageshack.us/img443/2926/capturelgw.jpg I need help getting this started. Does anyone understand that R1, R2, R5, R6-11 are 100k, but then what's that -1.0 M doing underneath? Also I think that R11 - 20k is a typo to mean R12 as the potentiometer. Id appreciate some...
  24. F

    Electronic Instrument Amplifier

    Need some help guys https://www.physicsforums.com/attachment.php?attachmentid=32237&d=1297816285 I began to analyze it and I got to this: OA2 is a non inverting amplifer OA1 is a voltage follower thus: V1(1+ (R1/R2) is the input for R3 into the final op-amp OA3 which is an...
  25. A

    Operational Amplifier: How Does It Work?

    Hi, I have a quick question regarding Operational Amplifier's. I understand in an ideal Op-Amp the current through the + and - input terminals should be zero. What is the point of the Op-Amp if no current goes through the inputs? How does it work? thanks
  26. H

    Help with bjt amplifier design

    Homework Statement given input as 100mV peak and expected output to be 10Vpeakto peak...i am having trouble on how to find the different values , like resistors , capacitors ...i am planning to use fixed bias circuit (common emitter configuration) and my transistor gives a value of hfe=...
  27. M

    Why Do We Treat Input and Output Impedances Differently in FET Amplifiers?

    Hi guys, can anyone tell me the reason why we set Vi=0 (short circuit the input side) when we want to find the output impedance Zo but we don't do the same by setting Vo=0 when we find the input impedance Zi? and why do we let Io=0 (open circuit the output side) to find the gain Av? thank you
  28. S

    After amplification of a signal through an amplifier

    hi... after amplification of a signal through an amplifier, the amplified signal is 180 degrees out of phase with input..why?? thanks..
  29. A

    What is a cost-effective way to design a high power opamp based amplifier?

    Can anyone please give me the design of a high power opamp based amplifier, Vcc(100-200V, single power supply), Output current(tens of amperes)
  30. P

    How to calculate the efficiency of an amplifier?

    How to calculate the efficiency of an amplifier e.g. op-amp? Been thinking about that, and have no answer. It should not be Vout / Vin ?
  31. P

    Is op amp or any amplifier circuit/device a over-unity device?

    Is op amp or any amplifier circuit/device a over-unity efficient device? The above question has been stuck in my mind, and I can't figure it out, as Vout is greater than Vin which Pin>Pout. So is it? I heard a lot about free energy and aether, thus come to this question.
  32. genxium

    Understanding AC Amplifiers: DC vs. AC Circuits and Oscilloscope Analysis

    Although this question may seem too simple, I still want to ask it on the forum because I’m really confused…… Here are the easiest amplifiers circuits for DC and AC currents, and what’s shown in the oscilloscope I’ve got in Multisim (corresponding), I want to know why ic/ib is negative in the...
  33. R

    Charge Sensitive and shaping amplifier

    Hi, we are designing a new radon detector which filled with two parts as CSA&SA(charge sesitive and shaping amplifier) in the total system. I attached a Circuit consisting of those two parts and i need to know the function JFET in CSA. In the given circuit i mentioned one arrow at the...
  34. A

    Amplifier phase difference

    greetings, i wonder if anyone could tell me that how and why there is 180 phase shift in single stage transistor amplifier circuit?
  35. S

    MOSFET Common Source Amplifier with Source Degeneration

    Why does the small signal voltage gain collapse as we increase the AC input voltage? Voltage gain = Av = (output voltage) / (input voltage). Both small signal (AC). When you draw the small signal circuit using T-Model, you can find that Av= (gm * Rd) / (1 + gm Rs) gm being the the...
  36. J

    Is this amplifier circuit connected correctly?

    Hi Please remember that I'm not a physics or science student. Just trying to learn things. So, please be simple with your replies. Thanks. I found this amplifier circuit on this webpage: http://www.circuit-lab.com/2009/12/30-watt-audio-power-amplifier-schematic.html Now I have connected the...
  37. H

    Prosthetic arm amplifier and filter design

    Hello... Am undergraduate EE, and am working on my final year project which is the development of prosthetic arm which will work on signal from muscles taken from surface myoelectric sensors. First of all i will explain about circuits i want to build, and i wish i will have comments...
  38. W

    Are Basic Electronics Enough to Build a Speaker Amplifier?

    How to build this amplifier ? Need what component!
  39. Topher925

    Methods to increase bandwidth of a transimpedence amplifier?

    Long story short, I'm trying to "easily" increase the bandwidth of a transimpedance amplifier which is limited by the intrinsic capacitance of the feedback resistor, R. The knee frequency is of course given by f = 1/(2*pi*R*Cr), where Cr is the intrinsic capacitance of the resistor. As...
  40. S

    Amplifier or Booster(Amplification of signals).

    I have 2 questions:(at least answer on question) 1) What is an amplifier? Is amplifier or a booster are same thing? What does an amplification do with signals? If an booster/amplifier is connected in a DSL line so will it amplify DSL connection to get better speed? 2) How to make a portable...
  41. F

    Where Did I Go Wrong in Calculating Avo and Gv for a MOSFET Amplifier?

    A Common-Source amplifier utilizes a MOSFET with µnCox = 400µA/V2, W/L = 10, and VA = 10V. It is biased at ID = 0.2 mA and uses RD = 6 kΩ. Find Rin, Avo and Ro. Also, if a load resistance of 10kΩ is connected to the output, what overall voltage gain Gv is realized? Now, what if a 0.2V peak...
  42. F

    Audio/Video DIY Hybrid tube/ss amplifier help

    Hello everyone, I'm in the design process of building a 100W/ch audio amplifier. I would like it to sound as good as possible (willing to sacrifice power output for sound quality) and am looking for some design pointers. The output stage and driver stage will be solid state using 2sd845/2sb755...
  43. K

    What Are the Noise Parameters of a Very-Low-Noise Amplifier?

    We need a very-low-noise amplifier for a special application, and we buy such an amplifier with a noise bandwidth of 2.4 MHz and an amplification of 1000. To test it, we take a set of "perfectly" shielded standard resistors, connect each if these to the amplifier input, and measure the rms...
  44. E

    Does the Presence of Rc Affect the Voltage Gain in a Common Collector Amplifier?

    Normally in common collector amplifier, Rc (collector resistor) is absent or otherwise it is short circuited by capacitor. My question is: If Rc is present and not short circuited, does it affect the voltage gain? If it does, how it affects? Appreciate if someone can present clearly in...
  45. L

    Assignment problem on Operational Amplifier

    The question is as given in the image attached entitled 'amplifier question' I would just like someone to check my working and verify whether it's correct or not. Thanks. And also want to ask on the second part which is 'what mathematical operation does this circuit perform?' Any help would be...
  46. N

    Inverting amplifier and sinunsoidal math

    Homework Statement I have an inverting amplifier with v(in)=0.001sin(2000πt) and v(out)=-5sin(2000πt + 25)Homework Equations what is the input amplitude and at what degree? what is the output amplitude and at what degree? what is the voltage gain and at what degree? The Attempt at a Solution I...
  47. H

    Why is my simulated inverting amplifier output not matching the expected result?

    Hi, I was trying to simulate a simple inverting amplifier in LTSpice. However, the results that I get don't agree with what I am supposed to get. Please look at the PDF attached. Based on the current law, it is easy to tell that Vout = -Vin. But I am seeing Vout = app. 0V. Am I missing...
  48. Y

    Intermediate frequency amplifier

    Homework Statement I'm supposed to design and build the intermediate frequency amplifier portion of an am receiver. Homework Equations The Attempt at a Solution I've been looking around online and correct me if I'm wrong but the intermediate frequency amplifier takes an ac signal, filters...
  49. M

    Output waveform of emitter amplifier

    Homework Statement What causes the output distortion seen in the above diagram? Output on right, input on left. The Attempt at a Solution This isn't homework, just something I can't figure out, playing with a simulator. The gain here is dependent on the input voltage... but why is the output...
  50. A

    Can a non-inverting op-amp circuit have Rf=Ri = 0? And what is its purpose?

    Homework Statement How does a non-inverting op-amp circuit work? What happens if you make a non-inverting amplifier with Rf=Ri = 0? What would be the purpose of such a circuit?
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