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. D

    Determining the value of beta to make the amplifier stable

    Homework Statement The open loop response A(jw) of particular op-amp is measured and is shown. The top figure shows magnitude plot of A(jw) in dB and the bottom figure shows the phase plot of A(jw). Determine the value of β in order to have a stable feedback amplifier? Homework...
  2. H

    Simple Common Emitter Amplifier

    Hey guys. I'm jumping into the world of electronics out of boredom and curiosity and am trying to wrap my mind around a few things. I'm on the topic of Transistors presently and have spend many hours learning about it's different modes of operation. I'm a bit confused about the Forward Active...
  3. P

    Cs_mosfet Amplifier Troubleshooting

    Hi all, I am studying cs_mosfet amplifier and i have simulate one simple amplifier with VDD=+12v Vs=1v ID=0.5mA gm=1mA/v Vd=6v. I am getting a signal that is amplified by gain -11.3 by calculation and also on simulation but when doing on hardware i am getting gain around -40 to -45 I...
  4. B

    Optimizing a BJT Amplifier Design for Specific Parameters

    The outcome is: design a single stage amplifier with the following parameters: Rin=1KOhms Rout=1KOhms Voltage Gain=15 corner frequency=300Hz specified Transistor is BC109BP AC supply, 0.5V DC supply 20V supply frequency, not specified, I have assumed 1K We have not been given...
  5. R

    What is the Frequency for Unity Loop Gain in Low-Pass Amplifier with Feedback?

    Homework Statement I need some help with the following problem (it is from an old test paper). Below is the Bode plot of the open loop gain of an amplifier: A constant fraction β=0.1 of the output is fed back to the input. This feedback does not load the amplifier. Using the Bode plot...
  6. S

    Help with Unity Gain Amplifier

    I need to design a unity gain amplifier for a sample and hold circuit. I've decided to use the circuit shown in the attachment. Now I know the gain = 0.5(Gm2*R1)[(Gm3*R2)/(1 + Gm3*R2)]. The 2N7000 has a Gm of 0.1, so that gets me the values of R1 and R2. I don't know if these are good values to...
  7. K

    Instrumentation amplifier: why subtractor block?

    Hi, I'm looking at a circuit of a classical instrumental amplifier having 3 opamps, 2 for buffer, with Rg to adjust the gain. The output from this buffer + gain circuit is then feed into a third opamp, in a circuit that is the 'basic' differential amplifier, but whose function now that Rg is...
  8. E

    Common emitter BJT Amplifier - maximum input voltage

    Here is my circuit: β=100, VCEsaturation=0.2V, VBE=0.7V, λ->0, VT=26mV After completing DC analysis I got these results : IB=18.05μA, IC=1.805mA, IE=1.823mA, VCE=4.658V>VCEsaturation=0.2V, gm=0.06943, rCE=∞ Ω, rpi=1.44kΩ. After completing AC analysis I got Av=-115.7, Ai=72.23, Rin=1.040kΩ...
  9. dwn

    Engineering Understanding Source Transformations in Operational Amplifier Circuits

    Homework Statement See ImageHomework Equations Source Transformations The Attempt at a Solution The answer is given, but I do not understand how they got it. When I multiply 9mA and 947.308Ω resistor, I get 8.526...what am I doing wrong? Also, could someone explain how they went on to get...
  10. J

    Why is Q1 on and Q2 off in this BJT differential amplifier?

    I don't understand why Q1 is on and Q2 is off. Can someone explain me the reason for that? Thanks in advance.
  11. P

    What are the internal mechanisms of the 741 Operational Amplifier?

    Hello, As I mentioned before, thank you for all the mentoring. It has been a huge help to my understanding. So, I am trying to stay one - two weeks ahead of my operational amplifiers class. I know that we will soon be discussing the 741 Operational amplifier. While reading about it, I...
  12. P

    Amplifier Comparison: CE, CC, and CB Types Examined - Study Guide"

    Hello, Thanks so much for all the previous help. I will probably be using this forum a lot this semester because my textbook is not very helpful. So thank you in advance. I am trying to create a comparison table of CE CC and CB amplifiers to help me study. However, I cannot find the...
  13. T

    BJT: Common Emitter Amplifier Gain

    So I have a question regarding the gain of common emitter amplifier. Referring to the attached diagram, the voltage gain of the circuit is -RC/RE. However, I don't understand how Vbb can be removed when completing the analysis. I've done the KCL analysis by hand and keep getting a gain function...
  14. X

    Simple Op-Amp Inverting Amplifier

    Homework Statement I need to find an expression for the gain in this circuit. I know it is an interting amplifier, because with the models we were given to look at, this one fits the inverting amlpifier. I've also constructed a simulation in a simple Java applet that I have. My problem...
  15. P

    BJT single stage amplifier we write gm=Ic/VT

    For BJT single stage amplifier we write gm=Ic/VT where VT is Thermal voltage whose value is 26mv. Now if we have a Darlington pair i.e. two transistor connected in CC-CC mode what will be overall gm. Will the collector current Ic be divided by 52mv or 26mv. (Because in gain equation gm comes)...
  16. gfd43tg

    Instrumentation Amplifier Breadboard layout

    Homework Statement I need to set up a blueprint for my instrumentation amplifier on a breadboard shown on page 5 of the attached document Homework Equations The Attempt at a Solution I'm not sure how 2 op-amp chips will make 3 op-amps for the instrumentation amplifier. I'm also not sure how...
  17. T

    Linear amplifier question, Coarse Gain/Fine Gain.

    I'm currently doing a spectroscopy lab where you use a scintillator and Cs-137 to obtain a Cs-137 spectrum. I calibrated this spectrum using the known gamma energy for Cs-137 at 662 Kev at the photo peak. I am now trying to use this calibration for a Co-60 spectrum. The problem is that when I...
  18. R

    How Do You Calculate Gain in a Transistor Amplifier Circuit?

    Homework Statement A typical transistor amplifier is shown in the Figure. Find the amplifier gain G. Circuit diagram: http://i.imgur.com/Rzv4JR7.png Vs = 280mV R1 = 100Ω R2 = 7kΩ R3 = 100Ω Vd = 4*10^5 Ib (Ib is current through R3) R4 = 7kΩ R5 = 900Ω Vo = ? (Voltage drop of R5)...
  19. D

    SR830 Lock In Amplifier Not Reading Reference Signal

    So here is my dilemma: We have our SR830 in a MOKE set-up. The modulation of the laser is with a chopper at approximataly 336 Hz. The reference signal is not being picked up by the SR830, but using the same cable the reference frequency is coming up on our oscilloscope. ie, plug the cable...
  20. Q

    Ai=Av*hfeA1=Ai*Rc/RbSolving Amplifier Questions with Low Frequencies

    Homework Statement We have an amplificator of low frequences like in the figure.The transistor has these h parameters: hie=1.1k Ohm,hfe=50 Ohm In the entrance we have Vs and Rs=10 kOhm. Find A1,Ais,Av,Avs,Ri,Ri',R0 and R0' Homework Equations There are many. The Attempt at a...
  21. Tesladude

    Converting split supply amplifier to single supply

    I am talking about those 5pin AB amplifiers like the tda2030 for example. You can power them with posotive and negative 12v, which is equal to a total 24v, Or you can modify the circuit for a single supply, but if you do that so you can use a single supply12v, is it equivalent in output...
  22. Tesladude

    Determining truth of 555 watt amplifier board

    Determining truth of "555 watt" amplifier board My math is showing that this amplifier is not 555watts but 140watts at 8 ohm at +-36v and 555 watts when shorting the output with ground. What do you guys think? amplifier board...
  23. Tesladude

    What safety precautions can I use for an amplifier?

    I do a lot of electronics and have built high power amps at home, I am making one for my dad and I am putting the outputs on delayed relays so you do not hear the pop when the amp turns on and off, but I just remembered that there are other instances which will turn off the relay for safety...
  24. O

    How does FET amplifier amplify?

    BJT ,the output voltage is amplified because there is dc voltage supply to keep BJT active ,but what about the FET? The voltage supplied only control the gate only, anything to do with the output? Thanks
  25. B

    Analysis of Cascode configuration Amplifier

    Homework Statement Homework Equations See above picture. The Attempt at a Solution I am stuck on the first part, i know i need to find the x intercept of the DC load line is at +Vcc, and I am pretty sure the y intercept is at Vcc/R7, but I do not know how to use this information to find...
  26. B

    Need help analyzing and audio amplifier [final exam study guide]

    Homework Statement Homework Equations See Image The Attempt at a Solution I am confused where to start this problem. Obviously i need to get at the DC load line for Q1. But the problem is that I was taught in class that the DC load lines intercepts for a transistor are...
  27. Tesladude

    Audio amplifier power supply question

    So I had an old home receiver which broke down so i took out the large transformer 6800uf caps and rectifier. This receiver put out 60 watts out of each chip so from my many hours of being on google in the past, the chips should require +-35v, and because of the increase in voltage after...
  28. P

    Calculating Amplifier Power Draw from +9v and -9v Batteries - 8mA Current

    Homework Statement Calculate the power drawn from the batteries by the amplifier. The batteries are +9v and -9v. The amplifier draws a current of 8mA from each of its power supplies. Homework Equations P = VI The Attempt at a Solution I'm just a little stumped as to what to do for the...
  29. JJBladester

    Determining voltage gain of instrumentation amplifier

    Homework Statement The following voltages are applied to the instrumentation amplifier in the figure. Vin1=5 mV, Vin2=10 mV, and Vcm=225 mV. Determine the final output voltage. Homework Equations R_{1}=R_{2}=R A_{cl}=1+\frac{2R}{R_{G}} V_{out}=\left ( 1+\frac{2R}{R_{G}}...
  30. B

    Audio amplifier physical noise+possible popped capacitor

    Hello, I have this audio amplifier from Vivax AM 100. But it has somewhat weird problem. When you turn it on it starts buzzing but, not like buzzing on speakers but rather circuit starts buzzing, rattling noise. There is also like wax residue on the board, which i don't think its...
  31. R

    Amplify Pressure Sensor Output with BJT

    I have a pressure sensor, it has 4 wires, In+ In- Out+ Out-. I excite In+ and In- with a 12V battery and the outputs are about 6V each, the difference is very small, 0.7mV at 1atm and 12.9mV at 100psi. I want to read this with a microprocessor which takes in analog 0-5V so I want to amplify...
  32. A

    How Can I Build a Basic Transistor Amplifier for My Phone's Speaker?

    Hi, I have a single 2 watt, 8 ohm speaker from an old radio that i wired directly to a headphone audio jack and tried it in my phone. as you can probably guess, my phones speakers are much louder. How could i make a basic transistor amplifier that could give decent volume from the speaker...
  33. S

    Ac coupling and offset voltage in amplifier

    Hey all, Just a question concerning the image I have provided. If I have an offset of 0.1 mV at the non inverting input, how exactly does coupling take effect in this set up? If I input an ac signal, it will pass through the cap, but will the op-amp not still experience the offset voltage?
  34. A

    Shaping time on my amplifier alters the gamma energy registered?

    Hi, My understanding of shaping time on amplifiers is that its the amount of time the capacitor has to collect charge. I would say that the longer the time the better energy resolution you would have due to that all the charge created from the photon is collected. However, if the time is long...
  35. Tesladude

    Can I use a 2A transformer to power 4 TDA2050 amplifier chips?

    So I want to make a tda2050 amlifier with 4 of these chips, and after posting a lot of questions about different audio chips here, the chips always turn out to draw a few amps EACH as said in the datasheet. On this chip it says a max of 5 amps and people always tell me to supply them with a...
  36. N

    How to choose Hfe in common emmiter amplifier circuit

    I am using a transister model BC107bp in multisim, and i found that its min Hfe is 40 and max Hfe is 450. If I want to construct an amplifier circuit, i should choose the min or average? I found most of the datasheet show the hfe of collector current at 2m A (min 200 - max 450), but if my...
  37. M

    Phase change in lock-in amplifier

    I just started to use a lock-in amplifier, and I am trying to following the procedures by adjusting zero phase. But my input phase changes with time and sensitivity, and I couldn't lock in onto it. The question is, is this normal that phase changes all the time during the experiment or if there...
  38. C

    Ideal op amp, difference amplifier?

    Homework Statement The OP amp in the circuit is ideal. Calculate V0 if Va = 2V and Vb = 1VHomework Equations V = IR KCL, KVL, voltage division, current division,Op-Amp Output V = (Gain)(V+ - V-)(Gain) = -Rf / Rin Ideal op amp properties: Input Resistance RI = ∞ Output Resistance Ro = 0...
  39. A

    Amplifier Distortion when Combining Stages in Series

    I am having some issues designing a simple amplifier circuit and was wondering if anyone could help me. I feel like I am missing something fundamental, but can't seem to grasp it. I'm using an AD826 dual operational amplifier using ±15 V supplies. I've breadboarded some very simple noninverting...
  40. H

    Differential Amplifier Common-mode Output Resistance

    Homework Statement I am learning about differential amplifiers, and am having trouble determining the common-mode output resistance. In the text, we have the two sections "Differential-mode gain and input and output resistances" and "Common-mode gain and input resistance." Notice the lack of...
  41. I

    Design a Tuned RF Amplifier with Gain 100 for 720KHz

    Hey...I was trying to design a practical of mine...There is this question where I am supposed to design a tuned RF Amplifier with gain 100 for a frequency 720KHz with BJT. I know that I will get frequency with LC tank circuit but the gain is a different story. I have searched 5-6 books and am...
  42. M

    Why is my amplifier not working with my speaker?

    Hey guys so I'm going to use this template because it said so in the stickies but my question isn't a word problem kind of thing. I am building an amplifier using this tutorial and am having problems. I have attached my schematic for it, however I'm fairly new to circuits and this project has...
  43. H

    Differential Amplifier: Neglecting ro, why?

    Homework Statement Pretty straightforward. Attached is a small signal picture of a differential amplifier. Summing currents at the emitter junction, the text says: "Because the transistors have resistive loads, the output resistance will be neglected in the calculations." Why is this...
  44. R

    Common-Emitter Amplifier (Collector Voltage)

    Hi, My question is regarding an example of a common-emitter transistor amplifier shown in my electronics book. Here is the diagram of this particular amp operating from a DC power supply: My book says: "the transistor has β = 99, with no signal applied the voltage at the base of the...
  45. H

    Common-Base Amplifier Current Gain

    Homework Statement Problem statement and solns. in attachment. Homework Equations Can anyone explain the equation for the current gain Ai? I do not understand where the divider temr comes from. The Attempt at a Solution
  46. D

    Impedance seen by input of inverting amplifier

    Hi, The book I'm reading references the fact that the impedance seen by the inverting input of an inverting amplifier is just the two feed back resistors, R1 and R2 in parallel. I'm having trouble seeing this. I understand how the basic voltage divider with one end at Vin and the other...
  47. D

    Non Inverting Amplifier Currents

    I'm confused by the fact that for the typical non-inverting amplifier, (1) The input current is ideally 0 A. but (2) The current going into ground is given by Vin/R1 where R1 is the resistor above ground. If Vin were provided by a battery for example, which has Voltage=0V on one side...
  48. H

    Solving Common Base Amplifier Problems: Homework Statement & Solutions

    Homework Statement The problem statement, given solutions, and my small signal drawing are attached Homework Equations Rout, Rin, Av The Attempt at a Solution To begin with, our text seems to alternate between using approximate equations and exact derived equations without stating...
  49. A

    Finding Feedback Polarity - Step By Step Guide

    Homework Statement I have to find the feedback polarity. I proceeded as follows : Homework Equations The Attempt at a Solution 1. As Iin = iF , increasing Iin will increase iF 2. Now drain current for MF is increasing so Vgs of the transistor should increase 3. That means...
  50. Tesladude

    Amplifier Circuitry w/ LM4780 IC: Adjust Output w/ Potentiometer?

    I am making an amplifier with 2 lm4780 ic The gain is set by a resistor between the output and negative,I want to use a potenciometer to be able to adjust this, so my question is: will lowering the ohms lower the output or will increase the output or what?
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