What is Amplifier: Definition and 557 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. F

    Infinite bandwidth of an ideal amplifier

    What is meant by the infinite bandwidth of an ideal amplifier? If some extreme frequency signals were to be input in an amplifier of limited bandwidth and in the ideal amplifier, what will be the difference in their outputs?
  2. Sotiris

    Problem with Lock-in Amplifier (cannot lock the signal)

    Hello, I'm using a lock in amplifier (model 5210 from signal recovery) for some experiments with photodiodes. Firstly, there is an optical chopper that "feeds" the lock in (reference signal). My input is a photodiode (in current mode). The problem is,the unlock (unlk) light is always on in the...
  3. F

    A question regarding electronic negative feedback

    I have a confusion understanding one of the basic assumption used for operational amplifiers which is Vin = 0 or difference of inputs = 0. Take for example an ideal amplifier with inputs V+ and V- V+ = 1 V- = 0.5 * Vout Supply Voltage = +-9 Vin = V+ - V- At start V+ = 1 and V- = 0, providing us...
  4. T

    Operational Amplifier Comparator Circuit

    Homework Statement The variation with time t of the potential Vin at the inverting input of the op-amp is shown in Fig. 10.2. On the axes of Fig. 10.2, draw the variation with time t of the output potential of the op-amp. (pictures attached) Homework Equations The potential divider equation to...
  5. Nikhil N

    Opamp as amplifier: Not getting the desired gain

    I want to amplify my input AC,50Hz to 30 times. I just started to test the basic inverting amplifier, with R2=4.7K and R1=1K. I varied the Vpp from 1 to 5 and I observed, I am not getting the gain of 4.7. Why this is happening ? One more doubt that I have is I used 12V Vcc, so if the input is...
  6. F

    Voltage offset differential amplifier

    Hi all! I am trying to simulate a differential amplifier in LTSpice but I'm having some troubles. First, I would like to know if you could suggest me some "basic", scholastic, MOSFET and BJT model, like the 1N4148 for diodes. Secondly I designed this: Practically when I get the drain output...
  7. Z

    Class AB or Class D for a home theater amplifier

    I am planing to assemble a 5.1 channel amplifier. I selected the famous TDA2030 as the basic element and is simple to proceed. But I have a confusion, whether to use some other Class D amplifier for better quality.Conceptually, a Class D amplifier is considered by some music purists to be less...
  8. A

    Operational Amplifier Homework Question

    Homework Statement What is the value of V2 in terms of Vos? Homework EquationsThe Attempt at a Solution In the class, we were told that this is just a non-inverting amplifier, thus V2= Vos x (R2/R1+R2). However, I want to work out the solution by applying nullator hypothesis (voltage...
  9. T

    Operational amplifier with feedback problem

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] Using the equations above, I'm not getting the right answer for beta which is 0.4926 V/A. Is my model wrong ?
  10. T

    Cascaded low-pass filter followed by a buffer amplifier

    Homework Statement 3. FIGURE 3(a) shows a simple low-pass filter followed by a buffer amplifier. (a) Write down the transfer function for the filter. (b) Determine the 3db frequency (fc) if R = 10 kΩ and C = 10 nF. (c) If four such stages are cascaded as shown in FIGURE 3(b), determine the gain...
  11. F

    Engineering Shunt feedback amplifier circuit

    Homework Statement The attached figure shows a "shunt feedback amplifier" circuit, and its AC equivalent model. Verify that: r_T = \dfrac{v_{out}}{i_{in}}=\dfrac{-R_B}{1+\dfrac{R_B+r_\pi}{(1+\beta)R_C}} (assuming R_B\gg r_e, where r_\pi=(\beta+1)r_e.) Homework Equations In the...
  12. F

    Estimating the upper 3dB cutoff in a MOSFET amplifier

    Homework Statement I've found the gain, but now I need to estimate the upper cutoff frequency with the open circuit time constant method, so the upper 3dB cutoff would roughly be $$\sum_{i = 1}^{n} \frac{1}{\tau_i}$$ The attempt at a solution I'm currently trying to make sense of the given...
  13. A

    Engineering Help with pnp BJT amplifier circuit

    {Moderator note: moved from technical forums, so no template} Hi, My mid-term quiz is next week. I have tried to solve this question but I'm stuck on Qn 4 Part H. Any hints?? Image for Qn 4: http://imgur.com/gb9jEfW My Answers for QN 4: http://imgur.com/a/fS3GM Can you help me check my...
  14. slick_willy

    Jobs in audio amplifier circuit design?

    Hey guys (and ladies), I am a junior year EEE student at CSU Sacramento and am hoping to get a job in audio amplifier design as a career after graduating. I have always loved music and electronics and working in this field would honestly be like a dream come true. As far as my experience in...
  15. B

    Engineering Effect of bypass capacitor on MOSFET amplifier circuit

    Homework Statement A bypass capacitor increases gain in the mid-band region. Explain how with the figure and small signal model. Assume gm=0.5mS. Homework Equations Rs = 1 k Ohm The Attempt at a Solution With the bypass capacitor, the source would be treated as grounded and the equations...
  16. T

    Common source amplifier low frequency resonse

    Here's the amplifier in question: I'm not understanding this part: Why is Cs not included in the current divider ? To my understanding of current divider, It = Id+Io, where It is the current flowing through Rd So, Io = It*(1/Cs)/(1/Cc2)+RL
  17. M

    Small signal analysis of a cascode amplifier

    Hello there. I am stuck trying to figure out the voltage gain of a cascode amplifier from a small signal analysis. The circuit seems to be under-determined for reasons I do not understand or maybe I am missing the perfectly obvious. Here's my small signal model: The only relation I can...
  18. M

    Amplifying a Photodiode using an OpAmp

    Dear electrical engineers, Here a question from a serious electronics n00b =D. I tried to build a system as shown in the image. I have a photodiode which gives me a clock signal in the range of 200 to 500mV. Frequency will be in the range of 100 to 1000 Hz. I would like to amplify this...
  19. B

    Connecting a load to a voltage amplifier

    Hi. This is a problem from an electronics textbook: The output voltage of a voltage amplifier has been found to decrease by 20% when a load resistance of 1 k is connected. What is the value of the amplifier output resistance? How is there an output voltage without there being a load? 80%...
  20. H

    Why do we need multiple amplifier stages in electronic circuits?

    I don't understand the need of amplifier stages if i want for exmple to amplify a small AC signal. Sure i get that it is used to improve the gain, but isn't an RC transistor amplifier made in such a way, that the collector voltage is equal to half Vcc in order to have maximum swing. If so, why...
  21. O

    Discrete Differential Amplifier

    Homework Statement Calculating the open loop output Impedance at 1kHz and the open loop differential gain The Attempt at a Solution Here is the approach. INPUT STAGE: Q111 and Q112 Av1 = Rtot/2re, where Rtot is the total resistance of R117 and the input resistance of Q78 which is Rin. So...
  22. teroenza

    Reference Pin on Differential Amplifier

    I want to use a differential amplifier to separate the digital and analog ground portions of a circuit, but am not confident in my understanding of the datasheet of the amps I have on hand (amp03). http://www.analog.com/media/en/technical-documentation/data-sheets/AMP03.pdf I think that...
  23. B

    Voltage Gain Calculation for 2-Stage Amplifier

    Homework Statement Calculate the voltage gain for each stage and the overall voltage gain. Homework Equations Ao (Gain) = - Rf/R1 3. The Attempt at a Solution [/B] For the first stage I got: Gain = - 15/10 = - 1.5 For stage 2 I got: Gain = -5.13.3 = -1.55 Multiplying the 2 together to get an...
  24. H

    Why named it parametric amplifier?

    Hello I have a seminar for my Optic Course in university with this title : Optical Parametric Amplifiers. I searched a lot but I couldn't find why its name "Parametric Amp" I think its about RF parametric amp.. Please if you know why named "parametric" share your knowledge with me. Thanks for...
  25. Enochfoul

    Calculate Unknown Voltages in Amplifier Circuit

    Hi Does anybody have any useful material on how to calculate unknown voltages in an amplifier circuit. Thanks in advance.
  26. A

    Finiding replacment for VISHAY sginal comditioning amplifier

    Hello... i have preety old Signal conditioning smplifers - Vishey 2310 (about 50 of them). they are over 20yo and they are conciderd to be very good but the time took its tole and i have only few that are functioning propely. can you recommend on last generation amps with the same spec? thanks...
  27. B

    Simple photodiode connected to lock-in amplifier

    Hello. I am currently modifying a semiconductor experiment. A laser beam is modulated with an acousto-optical modulator and illuminate the semiconductor sample. The sample is probed by microwaves. The reflected microwave signal go through a demodulator, and then in a lock-in amplifier. Then I...
  28. M

    How does an amplifier inadvertently demodulate a radio signal?

    I know sometimes speakers/amps will pick up a radio signal. I'm confused as to how the signal is demodulated accidentally. Are the signals picked up exclusively AM, or do FM signals get picked up as well?
  29. R

    Designing a High-Gain Differential Amplifier: How to Meet Specific Requirements

    The figure shows a differential amplifier with a differential input vid = (vin_d_pos - vin_d_neg) between the bases of Q1 and Q2, and an output (out) at the emitter of Q4. I have to Determine R1, R2, R4, R5 and R6 so that the following requirements are met: R 1 = R 2 Av = vout / vid = 100 [V /...
  30. Salvador

    Few smps and/or amplifier questions

    Hi folks , maybe you can help me out , so I've built a powerful smps with two separate transformers and secondaries being driven by one common two IGBT half bridge topology. I have also put 4x500w rms amplifier channels into the box , they are not kit's they are basically discrete component made...
  31. M

    Designing a Line-Out Amplifier for TRS/phone connector

    I have a signal that comes from a computer of phone line-out and I would like to amplify or apply analog filters. I am not sure what considerations I need to make in the design. What type of load should I present to the phone? What are the signal levels? Input or output impedance? Is there a DC...
  32. Hyo X

    Reduce Amplifier Drift when load is near input impedance

    I built a voltage amplifier based on the AD625 instrumentation amplifier. This chip has a 1 G-Ohm input impedance. When the load has a resistance of 100 kOhm, output drift is negligible. When the load has a resistance of 100 MOhm, output drift is significant and not acceptable. Are there any...
  33. G

    Opamp Summing Amplifier: Finding I1, I3 & V2 for Vout = 2V

    Homework Statement i know that it is a summing amplifier and i have vout at 2v, however in the question it asks for I1,I2,I3 and V2(vin) i have I1 and I3 but having trouble working out I2 and V2 Homework Equations Vo = - RF ( V1 / R1 + V2 / R2 + V3 / R3) The Attempt at a Solution when...
  34. CameronRose

    Amplify Position Sensor Circuit

    Hi everyone, I'm working on a college project this year about mountain bike suspension damping. By trade I'm a mechanical engineer however, I'm required to construct a simple sensor circuit to monitor the performance of the damper I am making. Forgive me if my wording or logic is not quite...
  35. T

    What Factors Determine the Performance of a BJT Differential Amplifier?

    Homework Statement Analyse the circuit to provide predictions for (a) the differential input resistance, (b) differential voltage gain, (c) single-ended voltage gain, (d) common-mode voltage gain, (e) common-mode rejection ratio (CMRR) in dB, (f) common-mode input resistance and (g) the...
  36. A

    How to draw AC equivalent circuit of CE amplifier?

    in the attached diagram its seen that while drawing AC equivalent of the common emitter circuit, Re is not taken in, the AC equivalent diagram no.2. why?
  37. H

    A question about common emitter amplifier

    Homework Statement Hello my fellow PF mates! Today i received my electronic textbook from Russia. The book is great, however i can't explain myself one single equation, but i hope you will help me:-) The question is about the blocking capacitor in a common emitter amplifier. R1 and R2 are the...
  38. V

    How do I get a DC difference amplifier working?

    I've been trying to figure out why my DC subtraction amplifier is not working, and am completely baffled. I have set up an op amp with no feedback resistors with voltages applied to both the inverting and non-inverting inputs as specified below. I previously had the op amp setup with a 10x gain...
  39. T

    What's the reason for modifying these amplifier circuits?

    If I have a bjt amplifier with pure differential input signals like this: Now let's say I apply pure common mode signals to the same circuit, then why is the circuit above modified to this ? Also when finding the Common Mode Input Resistance the circuit above excludes RE and includes ro...
  40. C

    Can You Help Me Achieve a 5x DC Gain for Opamp Output Voltage?

    Hello, I need an opamp that can output +/- 150v without paying $500 for a high voltage opamp. I need a workaround solution, I'm thinking of a 5x DC gain of the opamp output voltage but I am totally clueless on how to achieve this. Any ideas?
  41. C

    Engineering Transimpedance Operational Amplifier Simulation circuit help

    Homework Statement (a) Derive the relationship between the output voltage V and the input current I; i.e. if V = kI find k in terms of R1, R2 and Rf. (b) Calculate the current I if Rf = 10 MΩ, R1 = 90 kΩ, R2 = 10 kΩ and V –0.1 V. (c) Model the circuit using PSPICE [using an ideal opamp] and...
  42. P

    Can you help with operational amplifier homework?

    Homework Statement Good morning everybody,I'm french and my english isn't good but I need help for this exercice please: I tried to do this exercice,however I'm not sure of my answers,can you tell me if they are good , or what mistakes I committed ? Here the exercice : 2. Revelant equations...
  43. B

    TV antenna amplifier noise calculation

    Homework Statement Hello everyone. A 4-way TV antenna amplifier has the following specifications: Bandwidth = 40-862Mhz Gain = 20dB Noise figure = 6 dB Max output = 85dBuV Input impedance = output impedance = 75 ohm Question 1: Calculate the required voltage on the input of the amplifier to...
  44. U

    Audio Amplifier Using TIP 147, 142

    << Obnoxious all caps post fixed by Moderators >> I have made an audio amplifier using an LM386 IC, but it does not amplify any sound from the microphone. Please help me to improve this using a Darlington pair or any other power transistor like the TIP147/142...
  45. PhysicoRaj

    Design an audio power amplifier

    Hello, I was dissecting an old TV when I came across a set of speakers. They're 8 ohms, though I'm not sure if they're 8w or 6w.. I decided to make my own portable speakers (mono), which could be connected by means of an aux cable to my smartphone. I don't know what's the output voltage of...
  46. brainbaby

    Operation of transistor in Opamp log amplifier

    In the figure it could also be possible to connect the transistor Q1 as a diode by shorting its collector with its base ..but instead it is done by keeping both base and collector at ground... The text have to say that if it would be connected the other way(i.e by shorting collector and base...
  47. PhysicsGuy99

    AC-Coupled Current Input to Amplifier

    Hello all, I am looking for a means of AC-coupling a current input to an amplifier http://www.thinksrs.com/products/SR570.htm . I found some methods to do this with a simple op amp set-up, but I am not sure how to accomplish this with this instrument. The reason I want to remove the DC current...
  48. S

    I want to create an ultrasonic generator amplifier w/ MOSFET

    Firstly, I'm only a beginner at electronics and most of my knowledge comes from googling things. I have (several) ultrasonic transducers (100 watt 40 khz) i'd like to drive with my ultrasonic generator (100 watts 40 khz) but I'd like to up the amplitude of my transducers because I want the...
  49. EngrHdr

    Dual Supply Summing Amplifier

    Hi everyone, I am trying to make a Summing Amlifier. I have simulated on computer where it is working correctly, but on real circuit it is showing some mal functioning. I am using OP 27 Op Apmp. The circuit diagram is attached. When I try to add DC voltage to AC sine wave, initially sine wave...
  50. Salvador

    Simple class A amplifier for a different reason

    Hi, so i have built some amps and power supplies before , even some real simple smps from a working circuit schematic but I have two high power npn transistors laying around and some old half baked circuit boards. I am interested can I make a real simple smps out of a 555 oscillator chip, and a...
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