What is Amplifiers: Definition and 104 Discussions

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. L

    Common-mode rejection ratio and Instrumentation and difference amplifiers

    Homework Statement 1. a) If we wish to record an ECG of amplitude 1mV in the presence of interference that causes a common-mode voltage of 100mV to appear on the inputs of the amplifier, then what common-mode rejection ratio (CMRR) do we need require if we need a signal to noise ratio better...
  2. 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.
  3. E

    Characteristics of Ideal Operational Amplifiers

    One of the characteristics of an ideal op amp is that it have infinite input impedance/resistance. Now, I want you to tell me if I am correct : The voltage source is likely to have some internal resistance. By having an infinite input resistance, no current is drawn from the voltage...
  4. N

    Unlocking the Mystery of Low-Pass Filters in Lock-in Amplifiers

    Hi I am reading about lock-in amplifiers, and I read that the low-pass filter in a lock-in amplifier acts as an "integrator", since much of the noise that ends up in the DC output of the multiplier will integrate to zero. How is it that the low-pass filter can do that? I would appreicate...
  5. S

    Help with Isolation amplifiers

    Hello. I need help in finding the following isolation amplifiers: 1. I'm measuring current of approximately 600 A using LEM current transducer LF 1005-S (which gives an output of 200 mA for 1000 A). LEM transducer need DC power supply, and i use bipolar 15 V dc power supply. I need isolation...
  6. S

    Difference between class E and F amplifiers?

    What is the difference between E class and F class power amplifiers and what are their potential applications? Thanks
  7. E

    Operational Amplifiers Homework: Solving for Voltage & Current

    Homework Statement http://desmond.imageshack.us/Himg853/scaled.php?server=853&filename=opamp.jpg&res=medium relevant equations v=ir (ohm's law) kirchoff's current law The Attempt at a Solution i'm concerned about the bottom left node in this picture. current into an ideal op amp is zero...
  8. M

    What to study for high power microwave amplifiers?

    The kinds of devices I would like to be able to design are magnetrons, klystrons, gyrotrons, and maybe free electron lasers/masers. My goal is not to get a job in the field, but to just have enough knowledge to build some of these things myself. My first thought is plasma physics and EE, but I...
  9. S

    E&M Fiber Amplifier Homework Solutions

    Homework Statement One of the most exciting developments in lightwave engineering is the Erbidium doped fiber amplifier (ERDF A). It is very quiet(low noise) has a bandwidth of hundreds of GHz and relatively low cost.The fiber is "pumped" by a semiconductor laser operating at 850nm and the...
  10. Femme_physics

    Trying to understand how operational amplifiers work

    So I'm looking at this non-inverting Op-Amp http://img140.imageshack.us/img140/6660/shomermofa.jpg Trying to understand how Op-Amps work. It seems rather strange they're saying no current flows from + to - because then how does the current from Vin spreads through? After all, there...
  11. P

    Can Digital Modeling Amplifiers Fully Replicate Classic Analog Gear?

    Musical-recording age Since the dawn of the musical-recording age, the preferred method of recording guitars has been to set up microphones in front of amplifiers and capture the sounds produced. This carried the limitations of eliminating the electromagnetic signal bleed from the amplifier...
  12. ?

    Why Is V_G at 0 in MOSFET Circuit Analysis?

    Homework Statement Homework Equations dI = \frac{\partial I}{\partial V_{GS}} dV_{GS} + \frac{\partial I}{\partial V_{DS}}dV_{DS}The Attempt at a Solution I was just wondering why \small V_{G} is at 0. I have solved the entire question (there are more parts :P), but I could only do it once...
  13. I

    Learning About Class A Amplifiers - Links & Resources Provided

    I have been reading various online tutorials on the subject. Does anyone have some good links they will share. I am trying to build my understanding of the class A amp so I understand what I am doing if I chose to build a Nelson Pass Amplifier. I have an understanding of transistors and...
  14. N

    BJT vs MOSFET Amplifiers: Understanding the Differences in Gain and Performance

    (This is not homework) Okay I'm writing a lab report and just writing some discussion. Also I am curious myself. I'm a junior in computer engineering. I want to discuss the differences between BJT and MOSFETs as amplifiers and anything like pros/cons for each. Also why is the BJT...
  15. T

    BJT Amplifiers - Loadline question

    Hello, I had a basic analog electronics course this summer. Now that I'm trying to design my own circuit with a bipolar junction transistor (both for fun and to prepare for the future), I'm finding I don't really understand how and why I have to follow certain procedures to get maximum output...
  16. T

    How Do You Calculate Ib, Ic, and Rb in a Transistor Amplifier Circuit?

    Homework Statement Find Ib, Ic and Rb of the following diagram where the current gain is 150 Homework Equations V=IR, and Ai = Ic / Ib The Attempt at a Solution I am having more trouble knowing how to divide the voltages and currents up in this circuit. I can't really show any...
  17. D

    Opamp logarithmic & exponential amplifiers

    So I was playing around with logarithmic & exponential amplifiers in my lab class. I was looking at the following equations: http://upload.wikimedia.org/math/7/7/6/77663157d5b97ceb2e3edac5f587a620.png and http://upload.wikimedia.org/math/b/3/c/b3c569c85552561e41dec916f6e8ebe8.png...
  18. K

    Transistor Amp Amplification: DC vs AC | Frequency Impact

    Homework Statement I'm interested in the difference between the way a transistor amplifier amplifies with DC and with AC. I know that a transistor amplifier connected to a DC voltage source will have a larger gain with a bypass capacitor than without. Is this also the case when connected to...
  19. P

    Operation Amplifiers for high frequency application

    Hi, We would like to connect an amplifier to produce the appropriate alternative current for a high frequency actuating system. Who here knows where I can find an opamp with the following charachtristics: 1) Non-inverting 2) Amplifies an alternating input current 3 to 5 times 3) Works...
  20. A

    Questions and Answers regarding Amplifiers

    Hello PF Members! I'm revising amplifiers so will post question here occasionally on topics which I don't understand. This isn't homework question as I am asking for my benefit but if you wish for it to be moved, it's fine. :) Here's my first question: I've seen the circuit model for voltage...
  21. R

    Non Inverting and Inverting Amplifiers

    Can someone please explain the difference between non inverting and inverting amplifiers for me, all I know at the moment is that the gradient of Non inverting amplifier is usually positive?
  22. S

    Regulator circuit for input profiling for power amplifiers

    Hi all, I am working on finding a programmable regulator circuit that can produce 0-12 volts for a power amplifier. It needs to be linear, with a DC input and control voltage so that a PC can be used to generate an input profile.
  23. Lisa!

    Klystrons which are used as amplifiers

    So I was reading about klystrons which are used as amplifiers, and I've got so many questions!:confused: 1st of all , what does an amplifier like klystron do? Does it incease the frequency of the input microwave? What does low power microwave mean? Are they low power because of lw frequency or...
  24. M

    What is DC offset in an amplifier and how can it be eliminated?

    Homework Statement Explain what is meant by "DC Offset" in an amplifier and how can you eliminate it ? 2. The attempt at a solution I think it is the deviation from the real voltage, but I am not sure
  25. R

    Making a 433MHz Phase Detector with Log Amplifiers

    My group had a design based on the http://www.analog.com/en/rfif-components/log-ampsdetectors/ad8302/products/product.html" which was going to do our task of phase detection by use of what I can best tell was just some log amplifiers and . Well the AD8302 is a TSSOP package and I cannot...
  26. S

    2 current amplifiers the same

    Hello, I want to connect 2 current amplifiers the same time and I want to be able to switch between them. How should I connect them? in series? Thanks in advance, //Stella
  27. S

    Difference between opamp & differential amplifiers

    what is the difference between opamp & differential amplifier?
  28. K

    Gain saturation in EDFA amplifiers

    Hi, Why for arbitrary high input power the gain saturates in EDFA (erbium-doped fiber amplifer)?
  29. I

    Decide between two new stereo amplifiers

    Homework Statement You are trying to decide between two new stereo amplifiers. One is rated at 130 W per channel and the other is rated at 200 W per channel. In terms of dB, how much louder will the more powerful amplifier be when both are producing sound at their maximum levels...
  30. J

    Calculating RoE for AC Equivalent Transistor Amplifiers

    Hey everyone, In my EET program we're going over AC equivalent transistor amplifiers. We've gone over how to do some of them in class but I can't seem to figure out how to find roe. I have the output characteristic of our 2N2222 transistor and made the DC load line but I'm not sure were to go...
  31. E

    Understanding Parallel Resistors in Common-Emitter Amplifiers

    Quick question, i have a formula for finding rc (the ac resistance in the collector circuit) which is rc=RC(collector) is the parallel combination of RL I don't understand that for the example they have RC(collector resistor)= 12K ohms parallel to RL=50k ohms = 9.68K ohms.. someone explain the...
  32. C

    Using Transistor Amplifiers to Create Pulsating LED's

    I want to amplify the current/voltage from a music source. Specifically, I want to use the varying signal to vary the light intensity of a system of LED's connected in parallel. Basically, I want to create pulsating LED's. What I'd thought of was using a sound signal from my ipod to do so. I...
  33. P

    Seeing tutorials about amplifiers

    Seeking basic tutorials about amplifiers! Hi i am looking after some good tutorial for amplifiers, and with amplifiers i mean Inverting amplifier, noe-inverting amplifier and diffrential amplifier. I should point out that i am a new about amplifiers atm. Kindly Pellefant ...
  34. madmike159

    Create a Reaction Test Circuit with LED and Electric Shock Feature

    I am trying to make a reaction test circuit where a LED comes on at after a random amount of time and the slowest player gets and electric shock. The switches they press turn on a relay to another circuit connected to the device which shocks them. I need to find a way to stop the slowest...
  35. M

    What is Optical Parametric Generation and its Applications?

    I have been working through the book: "Almost All About Waves" John R. Pierce Dover 2006 This is a fascinating read & offers some deep insights into the inner workings of waves, from a practitioner's perspective. Chapter 13 - Parametric Amplifiers - is extremely interesting & is...
  36. D

    Understanding class A & B amplifiers

    I have read some texts myself but the explanations i read still leave me some queries. Below I have copied some text from wiki. From the text is in bold and my queries are in italic. Can someone please help me with my understanding, THANKS! Class A amplifiers are the usual means of...
  37. B

    Solve Urgent Amplifier Help: Microelectronics CD Player Problem in Few Hours

    Urgent help with amplifiers please! Hi, Please I need help for this problem. It is due in few hours! The main problem is that I don't succeed to visualize the problem to make a drawing. please, can someone help me? (the context of the course is microelectronics on amplifier) A...
  38. C

    Anlysis of transistor amplifiers

    i don't understand the difference between low ,high,midfrequency analysis of transistor amplifiers...what's midband analysis?
  39. S

    Class A amplifiers formulae help

    HI guys! well! i have got a question with me. Some forumlae i know and some i dont! please help me in solving it. There is a single stage class A amplifier which has Vcc =20V Vceq = 10V Icq = 600 mA RL = 16ohms Ip=300mA. We have to find: 1) DC Input Power 2) DC Power Loss in...
  40. S

    Learning Vacuum Tube Amplifiers for Senior Design Project

    Hey all; None of my EE classes cover vac tubes since they're largely obsolete. The thing is, for my senior design project (I have a year or so, no rush.) I'd like to build an audio amplifier. From experience I know the advantages of vac tubes and am willing to put up with the drawbacks...
  41. N

    Connect the two amplifiers to give me 1100 watts

    hi can i connect two amplifires to one speaker. i have sony amplifire 500 watts and JBL amplifire 600 watts. and two speakers 800 watts. Q i want to connect the two amplifires to give me 1100 watts to look like one amplifire. thanx
  42. J

    Distance Amplifiers: Mechanical Devices for Increased Distance?

    Question: Just as there are block & tackle that amplify weight handling, for example, a man pulls down on a rope with 10 lbs of force and lifts 100 lbs as a result: Are there mechanical devices that amplify distance? E.G. a man moves down a 100 lbs weight 4 feet and thereby moves upward a 10...
  43. S

    Amplifiers used in Radar Immunization ?

    amplifiers used in Radar Immunization ?? HI Guys! well! i have read somewhere that the waves generated by a primary radar adversley affect the electronic components of the vehicles that travel in the vicinty of the airport. To immunize these effects, TWT amplifiers and Class C amplifiers are...
  44. N

    Exploring Car Audio Amplifiers

    Hello everyone. I have been roaming around these forums but just finally decided to join. I did not exactly know where to post this so bare with me if you will. Anyways, I am in my second freshman semester as an EE undergrad and I am taking Honors Physics II. As a requirement of this...
  45. J

    How Does Energy Compensation Occur in Amplifier Systems?

    well i have this simple question, its about the energy in a amplifier system, whatever class is it, you have at first a tiny electromagnetical signal in the space with an amplifier system with its resistances, condensers, transitors,coils, calculated to work on certain constant voltages and...
  46. C

    What Are Good Resources for Learning About CE Transistor Amplifiers?

    Hi, Does anyone have any good resources on CE transistor amplifiers? Preferably ppt presentations or something... I've done the preceding questions, but i can't do 30a... How would i go about doing it? Thanks
  47. M

    Input impedances for both inverting and non-inverting amplifiers infinity?

    are the input impedances for both inverting and non-inverting amplifiers infinity?
  48. D

    Calculating Closed and Open Loop Gain for Inverting Amplifier

    hi all i got this operational amplifer question was wondering if anyone can help out 1. a feedback amplifier has a closed loop gain of 100, and the negative feedback is 0.8% of the output signal. the opamp has an open loop gain which is considerable less then the ideal value of infinity. a)...
  49. T

    Gain of the system of amplifiers

    I need help with the two questions below please because i just don't understand it !1 Questions 1. A signal processing system consists of a preamplifier, an amplifier and a filter connected in series. At a given frequency the preamplifier and the amplifier have gains of 12 dB and 31 dB...
  50. C

    Frequency Response of Amplifiers (BJT and FET transistors)

    Hi, I have a question pertianing to the effect of capacitance of BJT amplifier circuits on the low and high frequency response of the amplifier. Why is it that the coupling and the decoupling capacitors, in effect, only affects the low frequency response of the amplifier, and why is it...
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