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. J

    Common emitter transistor amplifier

    Rc= 5k ohm R1=100k ohm R2= 27k ohm Re=3.3k ohm beta=200 Vs=12.7V Vce= 0.3V at saturation With no signal applied, dc voltage btw collector ans ground measured as 7.7V Calculate the transistors base,emitter,collector currents Ive only come across problems with transistor in linear...
  2. X

    Differential Amplifier not working properly.

    I want to learn more about Op-Amps and amplification so I am making a simple differential amplifier. The circuit looks like this... I set it up and it isn't working correctly. First I tried putting 3 volts for Vin+ and ground for Vin-, and the voltage across Vout was around half a volt...
  3. S

    Deriving Vout in an inverting operational amplifier.

    Pls does anyone know how to derive for Vout1 and Vout3 in terms of Va and Vb for an inverting operational amplifier. Thank you.
  4. E

    Creating a signal amplifier using circuits

    Let's say I lived in a big house, and in my big house I had a wifi connection that was fairly weak. So weak, that inside of my room I would only receive one bar of signal. How would I design a circuit that would catch the wifi signal, amplify that signal, and rebroadcast it inside of my room...
  5. M

    Calculating variable gain for difference amplifier

    Homework Statement http://img706.imageshack.us/img706/263/hwstatement.png Homework Equations KCL/Node voltage method Ideal op-amp rules The Attempt at a Solution I solved a previous, similar problem where the gain was fixed and the resistor mass going into the inverting and noninverting...
  6. R

    Saving an LM324 Amplifier with YUNGMAN's Trick

    Hello. This post is mainly dedicated to YUNGMAN. I used your trick with Transorb in a class B amplifier driving coils. Unfortunataly these Transorbs introduced more than 1 nF capacitance and so the amplifier produce a large high frequency oscillation. Without Transorb, one more time LM324 is...
  7. xortan

    Single supply instrumentation amplifier

    Hello, I have attached a picture of the circuit I am working on. I am wondering where should I put a bias circuit when I also have a virtual ground?
  8. N

    Basic question: What is amplifier saturation?

    Hi all, I'm confused about saturation and cut-off. I've heard it described a few ways. Here is a very basic description of them. Explanation 1. Saturation occurs above the maximum input voltage within the linear range of the amplifier. Cut-off occurs at below the minimim...
  9. N

    Capacitors in common emitter audio amplifier

    Homework Statement Hello. When I looked at my lab manual, I saw the capacitor CB is connected in reversed direction. The AC source is connected to resistor RS, then connected to the negative polarity of CB. But I have no idea why it connects in reverse. Can please anyone tell me the reason...
  10. N

    Impedance of an emitted audio amplifier

    Homework Statement I drew the emitted audio amplifier in the picture below. When I looked at my lab manual, it says the impedance should be Zin and Zout, which Zin = R1*R2/(R1+R2) and Zout = Rc I have a few questions about impedance relate to this circuit: 1.) I saw the...
  11. S

    Common Emitter Amplifier Analysis

    This is my analysis of common emitter amplifier. Ic = βIb Ic ≈ Ie (because Ib is very small) => Ie = βIb Vcc = IcRc + Vce + IeRe Vcc = IeRc + Vce + IeRe Vce = Vcc - βIb(Rc + Re) Vb = IbRb + Vbe + IeRe Vb = Ib(Rb + βRe) + Vbe Gain = Vce/Vb Gain = (Vcc - βIb(Rc + Re))/(Ib(Rb + βRe)...
  12. R

    Protecting an LM324 Op-Amp in a Vacuum Tube Deflection Amplifier

    Hello. Here joined is the schematic of a small deflection amplifier. Outputs H0 & H1 are connected to electrodes placed in a vacuum volume. These outputs are protected by varistors. High voltage to collectors is 200 V DC. Sometimes, not very often, the head Op-Amp (LM324) is burnt. The only...
  13. C

    Why does negative feedback stabilize an operational amplifier?

    I'm studying for an exam and I'm struggling to understand op amps, here's my problem: I understand that for an op amp to have a controllable gain, the difference between the input terminals must be very very close to zero (and you can assume it is zero). And to do this you use negative...
  14. P

    Engineering Amplifier circuit for 1st year project using bjt's

    Homework Statement The question states that a 3 stage amplifier needs to be designed with a 2W rms to an 8ohm load. the amplifier must consist of a pre amp stage and a power stage. (using only bjt's) Homework Equations Up till now we have learned about small signal model, DC biasing, ac...
  15. Y

    Operational Amplifier Circuit for Adding AC & DC Signals

    I need a circuit that adds an AC signal with magnitude of 25mV and a variable DC signal between 0 to 5V, and applies it to a diode.
  16. D

    Placing electrolytic capacitors in an amplifier circuit.

    I am working various amplifiers in my labs. On nearly all of these amplifers (CC, CE, or CB), the input signal is capacative coupled. However, the cricuit schematic indicates the use of a polarized capacitor. The capacitors I am using are rated at a maximum voltage of 50V. Most of the voltage...
  17. perplexabot

    A difference amplifier question

    Hi. I am trying to find out what R4 is for or what its job is. Can anyone help? Thank you.
  18. S

    Confused with Omp Amplifier Problem - Part B Solution

    i am confused with this problem , part b : http://img85.imageshack.us/img85/1736/ampe.png my question is : Does Vsat reffer to the right amp or the whole circuit ? or something wrong with this problem ? thanks :)
  19. S

    Understanding KCL and the In=0 Principle in OMP Amplifiers

    i came across an example in my textbook as shown : http://img593.imageshack.us/img593/8444/img1314i.jpg if we used KCL and In = 0 : In = I_100 + I_25 => I_25 = -I_100 but as being written in the answer , I_25 = I_100 ! could anyone explain it for me ? thanks
  20. N

    Lock-in Amplifier & Square Wave: How to Get DC-term?

    Hi Usually when a lock-in amplifier is introduced to students, it is done when the input signal is a harmonic function and the reference is one as well. This is a nice concept, and it is easy to see how a DC-term propotional to the (desired) incident amplitude can be obtained. My question...
  21. K

    Engineering CE Amplifier Small-Signal Equivalent Circuit

    Homework Statement i am able to derive out node B and node C, but got stuck at node E. Can somebody please help me out with it? Homework Equations node analysis The Attempt at a Solution i used microsoft to show you my steps as there are too many subscript.
  22. M

    Amplifier efficiency calculations?

    Would the efficiency calculated using the P output/P input x 100 get the same answer as calculating the efficiency using the RMS input and output values? If so why?
  23. B

    Amplifier for electret microphone

    So I posted a question regarding amplifying signals from electret microphone. I had a problem, in which I had to design such amplifier which uses unipolar power supply. I was suggested LM386, and I got somewhere. Its very neat little amplifier, but I still need more. I tried a lot of things...
  24. Z

    How Can I Convert a -0.1V to 1V Output Into a 0V to 4V Range for an ADC Input?

    Homework Statement I am given a thermal sensor that measures temperature at 10mv/degree C. We are to measure a range of -10 to 100 degrees C. Design a circuit that will connect the thermal sensor to a micro controller with an A/D Converter the must take an input from 0 to 4v...
  25. S

    What is the input impedance of a FET amplifier circuit?

    Hello all, In one of our labs we determined the input impedance of a FET amplifier circuit via a potentiometer. We were told it was due to "maximum power transfer theorem" (something we have not learned yet). Essentially we attached a potentiometer in series with the input of the circuit and...
  26. G

    Component selection for special purpose amplifier

    Hello all, I have an amplifier in mind, you could think of it as an ac coupled differential amplifier, where the coupling capacitance is extremely small (<1pF) and you can assume the input is a sinusoidal differential voltage function. The amplitude of the source is over 1 Million volts...
  27. B

    Audio amplifier using only 1 op-amp [single supply]

    As the thread suggests, I am trying to amplify the signal from a microphone. Now, I have a circuit which uses 2 op amps with dual supply. That circuit works pretty well. I have to make now, a amplifier using only one op amp, single supply. The sound itself isn't of much...
  28. M

    A high power current amplifier circiut?

    A high power current amplifier circiut? Hi everyone! My research field is robotics and in one of my designs, i need to amplify a minor current to a current with very high amplitude (power amplifier). it almost could be able to amplify 0.5A to 20A. and as my robot is a mobile robot, such...
  29. A

    What is a Summing Amplifier and how does it work?

    Homework Statement Please refer to attached image! Homework Equations Absolutely no idea how to start this problem! The Attempt at a Solution A) I would think that there are 4 input combinations for this circuit. B) 0110 = 6v? C) No clue D) 1011 = 11v? E) No clue
  30. W

    How Can I Achieve Low-Noise Amplification of 1nA to 1V?

    Hi Guys and Gals, I am trying to linearly amplify a 1nA-10nA current to 1V-10V. I need at least 10KHz bandwidth. I have tried using a 3 stage amplification (negative feedback) system using an lt1012 op-amp (1 nA to 1mv, then 100,10 gain), but the noise is very high (-30/40 db). I need at...
  31. L

    Problem on Operational Amplifier

    Hi, Just I really short question. I have attached my assignment as a picture file. Don't worry I am not asking you to give me a solution. I just want to know, in the question it tells us that there is a internal resistance of 1MΩ, and a supply voltage of 10V. I am really confuse, as all...
  32. P

    How Does a Laser Differ from a One-Atom Photon Amplifier?

    What is the difference between a laser and a one-atom photon amplifier? Can we just say that a laser is many one-atom photon amplifiers put together? Is there any difference in the resulting photon statistics?
  33. L

    Input impedance of BJT amplifier

    Homework Statement Find input resistance of the ckt (see attached) Homework Equations The Attempt at a Solution Q2 is diode connected, so I replaced Q2 with VBE resistance (rbe or r∏). So, Rin is rbe1+(β+1)rbe2 But the answer is somewhat different, it's rbe1+ (β+1)...
  34. G

    Inverting operational amplifier circuit won't work

    I'm making a simple circuit on the breadboard with a 741 op amp. The feedback resistor is 150 kohms, and the input resistor is 100 kilo ohms, means the gain is 1.5. The input voltage is about 5.33. The power supply is ±18 V. For some reason the output voltage is 0.98 V instead of the amplified...
  35. T

    Radio frequency amplifier and error rate

    Hi, I am designing an RF link. Before my spectrum analyzer, I have an RF low noise amp with a NF of 2.5 dB. Without this amplifier, my error vector magnitude or error rate is 2.1%, after an amplifier it goes down to 0.7%. My question is, the receiving signal will have its own SNR and with...
  36. I

    Building a Simple Amplifier Circuit With High Slew Rate and Bandwidth

    Hello all, I have been building a simple amplifier circuit(diagram attached) that will take in a source voltage and use a resistor divider to divide the voltage down on three different ratios, determined by a manual switch- 1/1, 1/4, and 1/40. It goes through a unity gain configuration...
  37. Femme_physics

    Differential amplifier with zener diodes

    I think I'm getting better at this ((thanks to gneill, ILS, ehild and technician :wink:I'm quite sure I got it right using the easy methods (formulas). I'm not too sure about my "check up" to my solution using KCL and KVL...I didn't solve the check-up all the way because I wanted to see if my...
  38. 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 -...
  39. C

    Designing Class A Amplifier with 12V Power Supply

    Homework Statement Designing a Class A amplifier for project with high voltage gain and high efficency or at least as high as we can get. It has to have a 12V power supply. We have the design but the when we add the power supply that converts the 120v ac to 12v dc our output voltage goes...
  40. F

    Help With Self-Biases JFET Amplifier

    Hi, I am designing a circuit where i first use a JFET transistor to a provide a voltage gain, the JFET is wired as a self bias. Following the JFET is a BJT transistor which i am using to provide a second amplification. I have an issue though with the output waveform of the JFET transistor...
  41. S

    Basics of Common Emitter amplifier.

    Hello experts! I have some question related to this configuration of BJT. 1)Why we use capacitor at the base of the circuit?(Answer: To decouple DC so that our signal that is reaching to base of the transistor is not to be DC shifted that's why it is called "Coupling capacitor". If it is...
  42. P

    Designing an Audio Amplifier Circuit: Tips and Components | Satya

    hi all, i want to design the following circuit. The circuit should listen to the audio and amplify the audio. could somebody provide me the circuit or help to design the circuit like which components shall i take for the audio input, the speakers what i have to select and additional things...
  43. C

    Designing a Class A Amplifier for Good Speakers, Inc.

    [b]1. Homework Statement EE3350 Electronics I Term Project "Power Amplifier Design" Objective: You will be designing a proper power amplifier for Good Speakers, Inc. The company will accept only two designs. One of them is Class A amplifier and the other one will be a Class B amplifier...
  44. S

    Emitter and Collector Resistance in Differential Amplifier.

    Hello experts! Image of Differential Amplifier is given below. Here in diff amp both transistor have same characteristics. Even +VCC and -VEE are of same magnitude. Everything is same. Hence, their RE and RC are also same. 1)If both emitter and collector resistance of both transistor...
  45. W

    Why does a buffer is used in an audio amplifier?

    Let a simple concept of an audio amplifier is to be designed like this (in BJT) : CC *CE* CE * OUTPUT ... and CC acts as a buffer. Why does a buffer is required for the amplification? Wouldn't it be much more simpler if CC is being canceled out? CC = Common Collector CE= Common Emitter...
  46. A

    Distortion in rc coupled amplifier

    hi, when i was making a rc coupled amplifier but as soon as i connect the input signal the signal gets distorted.can anyone tell me the reason for that and how to avoid the distortion? thanks,
  47. jegues

    How to Design an Effective Microphone Amplifier?

    Homework Statement We are attempting to design a amplifier for a microphone. The end goal is to amplify what is being said through the microphone specified below through a set of speakers or headphones. See figure attached for the design parameters as well as the parts list we are given...
  48. B

    Learn Differential Amplifiers: Solve Emitter Voltage Mystery

    Hi! So I am trying to understand op-amps. But before I could learn op-amps, I need to be sure, what an differential amplifier is. I need someone to guide me a bit. Here is the picture I am trying to study. [PLAIN]http://pokit.org/get/b2b5162f1052656a75c035cf8452131b.jpg It says here, in...
  49. A

    How to Build a Simple BJT Differential Amplifier with a Gain of 20?

    Does anyone know how to build a simple BJT Differential Amplifier circuit? And also need to gain around 20..emergency please help. Thanks for that. As I build a circuit but is not simple enough, please have a look for that and any comment for this circuit?
  50. J

    Trying to find a simple amplifier design/signal conditioner

    I have a sensor whose output voltage, in the conditions I plan to operate it in, will be between 4.5V (max) and 3.5V (min). I want to increase the resolution of the ADC measurement of this value, so I want to create some kind of amplifier or signal conditioner that can change this range into a...
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