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.

View More On Wikipedia.org
  1. E

    Transistor radio amplifier noise in the 70s

    In the 1970s, did transistor radios have RF receive sensitivities down to the 1 microvolt level? If not, what is the highest microvolt it could resolve? But how could it do that? Even modern amplifiers have much noises. For example, at 100kHz, and a very quiet circuit with total noise of...
  2. E

    Engineering H-parameter model for non-inverting amplifier

    For a standard non-inverting amplifier as below: With nodal analysis, I got $$\frac {v_o} {v_i}=\frac {R_EZ_o+aZ_iR_E+aZ_iR_f} {R_ER_f + R_EZ_i + R_EZ_o + R_fZ_i + Z_iZ_o + R_EaZ_i}$$ However, with the feedback network of the amplifier converted to a h-parameter network as below: With nodal...
  3. E

    Stability test for Feedback Amplifiers

    Does the following simple test deduced from Nyquist criterion also apply to positive feedback or it needs to be modified? If magnitude of loop gain i.e. |T (jω)| > 1 at the frequency where phase(T (jω))= −180◦, then the amplifier is unstable. Reference: Analysis and Design of Analog...
  4. Z

    Why does amplifier sink power for Vout>0 and sources power for Vout<0?

    TL;DR Summary: How do we show that the dependent current source in a single-stage amplifier sinks power for ##v_{\text{out}}>0## and sources power for ##v_{\text{out}}<0## I am trying to solve a problem set from MIT OpenCourseWare's 6.002 "Circuits and Electronics" course. There is a problem...
  5. A

    B Amplifier or oscillator for a vibration generator

    I purchased this vibration generator to construct a Chladni plate. I was hoping to use it with my existing oscilloscope (which appears to be very old). It seems the oscilloscope is not giving me a signal strong enough to drive the generator. Any suggestions for a different amplifier or power...
  6. hilbert2

    Receiving High Freq Signals via Passive Downconverter

    I'm getting this type of device in mail, it is a passive microwave signal downconverter that converts a signal of up to 3.5 GHz to something that can be received with an RTL-SDR of upper frequency limit less than 1.5 GHz. Is it expected that I have to put the antenna-received high freq signal...
  7. B

    High power RF amplifier at fixed frequency

    Hello! I have a signal at fixed frequency of 4 MHz and amplitude of 0.075 V. I need to amplify it to ~75 V with the same frequency. I checked online a bit and I found either cheap amplifier that can't amplify this much, or very expensive ones that (almost) can (I might need to use a smaller...
  8. G

    How to wind a 5K audio tube amplifier transformer?

    60 watt tube amp needs a 5k primary and 8 ohm secondary transformer. I have wound voltage transformers on my lathe many times. Audio transformer is no different. Online impedance transformer calculator says, 5k to 8 ohms in 25:1 ratio. Online info says, audio transformer should be 60w x 5 =...
  9. cnh1995

    Engineering Differential amplifier confusion (BJTs + Operational Amp)

    Here is the circuit diagram provided in the book. In the solution, the book has used the following approach (red markings in the image): Input to the left transistor is 2V. Considering base-emitter junction drop to be 0.7V, the emitters are at 1.3V (left red arrow). Now, using the "virtual...
  10. S

    Power Amplifier and Exciter, Impedance / Power

    Hello. I have a question regarding an power amplifier (signal generator). I have three exciters and want to connect them to the power amplifier. One exciter have a impedance of 8ohm and power of 25 watt. The ampliefier have one output with the electical data: 4 ohm : 500watt; 6ohm: 330 watt and...
  11. A

    Engineering Small Signal Input Resistance of a BJT amplifier

    The diagram of the BJT amplifier small signal model is below. This is not really a homework question as I am self-learning electronics, but I was advised it may be better placed here than in the technical portion of the forum. Thus I do not have an "attempt" at a solution (which is given as RI...
  12. A

    Differential Amplifier Common Mode Thevenin Equivalent

    I am currently reading about small signal analysis of a MOSFET differential amplifier. The text I am using has the below two figures for a common-mode equivalent circuit for the amplifier. The first makes sense to me except where it calls it a "Norton equivalent circuit", whereas I thought a...
  13. A

    Need Help Building an Audio Amplifier with D2059 Transistors

    Good morning Thank you very much for being part of this forum. I have a concern. I have 4 D2059 transistors and I want to build an audio amplifier, but I don't have enough knowledge of electronics. And I have one more transistor tip117. Can anyone help me by sending a simple circuit diagram how...
  14. A

    Audio/Video Please help, require schematic diagram of power amplifier ROYAL L1200

    Hi to all much appreciation for you all,please is there anyone who can help me the schematic diagram of power amplifier ROYAL L1200
  15. fatima ece

    Lock-in amplifier with pulsed sinewave

    Hi, I am trying to use the SR865A lock-in amplifier to measure the frequency of a pulse of a sine wave( example: waveform below), - the sinewave signal is only ON during finite time not continuously-, I am using an external reference signal that is also a pulse of a sinewave with the same...
  16. A

    Engineering Voltage gain for amplifier (JFET) in common gate

    First the hybrid model, I assume the capacitor works as a short circuit regarding the altern current: $$A_V=\frac{v_o}{v_i}$$ $$v_i=-v_{GS}$$ $$v_o=-i_LR_L$$ $$i_L=g_mv_{GS}+\frac{v_{DS}}{r_d}$$ Now I use the Kirchhoff's law to get $v_{DS}$. I consider this close loop: $$-v_i-v_{DS}+v_o=0$$...
  17. Stonestreecty

    Heavy Amplifier Circuit Oscillation Happened

    Hi, all I am experimenting with audio amplifiers for a while now. I learned how to do an operational amplifier with discrete components and understand all its section and sub-circuits, recently. Then I decided to just skip the hard part and use operational amplifier and output power stage for an...
  18. brainbaby

    Calculating Input impedance of a CC amplifier

    Hi friends, Here is a CC amplifier The objective is to calculate its input impedance. Two ways are employed. *calculating input impedance using series resistor method (manual method) (refer first two attachment) V1 = 1mV = 0.001 V V2 = 656.4129mV = 0.6564129 V R = 1K Iin = 343.83207µA =...
  19. song youngill

    Engineering How is (1/2)V_id expressed in this circuit?

    As you can see in the picture, 1/2vid is entered in each of Vin1 and Vin2 on the left. Assuming Vcm is 0, I need to configure this circuit with ltspice, but I am not sure how to configure this vcvs. I'd appreciate it if you could tell me how.
  20. P

    Engineering Alternative design for a CE-CC cascade amplifier

    Here is a common CE-CC cascade amplifier- Here, the output of the emitter amplifier is directly connected to Q2, without any coupling capacitor or any voltage divider bias. This may harm the base-emitter junction of Q2 in case of unwanted output voltage from Q1 collector. But in that case, the...
  21. P

    Investigating the Effects of a Common Emitter Amplifier

    Summary:: Using a common emitter amplifier to pump up the input voltage, and studying the effects henceforth. Here is a circuit with 0.6V pk-pk input voltage (v_in) for the CE amplifier, 1.17 kHz frequency- For this, without C5 and R9, the AC and DC gain was -10. I was supposed to increase...
  22. Stonestreecty

    Troubleshooting LM311P Output Issue - Tips and Suggestions

    Hello, all For this little project, I'm using a LM311P. It is has a collector/emitter output. Because my circuit didn't function the way it should, I started debugging. With the collector unconnected the emitter (pin 1) still sinks (11 mA) and sources (20 mA) current, when applying a square wave...
  23. I

    Input Resistance of this BJT Amplifier

    Hi i got a question ,how do i calculate the input resistance ,of the RS resistor ,so i would get half of the voltage of the voltage source (500mA) .I've created the circuit in ltspice and found out that its around 95K ohms to get 250mA,but how would i calculate it . Ive also attached my...
  24. hugo_faurand

    Amplifier for piezoelectric sensor, OP Amp circuit

    Hello everyone ! I'm working with a piezoelectric cell and I need to retrieve the variation of the charge of the cell as a voltage signal. I found this circuit (a charge amplifier) with an OP Amp ( here the piezo cell is represented as the current source with the capacitor and the resistor on...
  25. I

    Two Stage Amplifier -- Find the Input Resistance

    Am trying to find Effects of Feedback - Input resistance of this circuit. Is this the formula that in need to use to find the input resistance of this circuit ?
  26. F

    Engineering Two-Stage Amplifier with Indirect Miller Compensation

    I don’t quite understand this question. I believe I need to find the W/L values for each transistor. I don’t have any equations in my lecture notes that relate these values to the given parameters. A point in the right direction would be appreciated.
  27. F

    Engineering What is the Open Loop Gain of an Amplifier?

    I’m totally lost and struggling to understand my lecture notes. Can somebody point me in the right direction?
  28. M

    I Checking for negative feedback in a circuit

    This is the circuit in question. During lecture, when checking whether this was negative feedback, my instructor said that if the v_out increases, then v- increases as well, which would lead to the next v_out decreasing because v_out = A(v+ - v-). I get how if v- increases the next v_out would...
  29. T

    I Two stage amplifier for a plastic scintillator

    When detecting a muon, we can use a plastic scintillator which consists of the components in the diagram attached. I am trying to understand what exactly the "two-stage amplifier" does which is located in the top left corner in the image attached? I am unable to find any information on it online...
  30. J

    Differential Amplifier with Two stages

    What I tried to do : First I tried to calculte vb1 : Saturation => Vds > Vgs - vth Vds > Vgs - vth Vd - Vs > Vgs - vth Vd= Vb1 Vb1 > Vgs - vth + Vs Vs= Vss Result : Vb1 > 0.4 - vth + Vs I don't know if it's correct and don't know what to do for the two others.
  31. M

    Engineering Common Mode Rejection Ratio: Instrumentation Amplifier Calculation

    Hi, I have a question regarding a practical CMRR calculation. Main information: - Signal input: 10 mV rms - Interference input: 1.5 V rms - In an earlier part of the question, we found that for the second stage of the instrumentation amplifier (the summation amplifier) that: $$...
  32. Jy158654

    How does the negative feedback amplifier below work?

    The book says that " The op-amp multiplies the potential difference between V+ and V- by the open-loop voltage gain to produce Vout." So my first question is, since we say we assume open-loop voltage gain is infinite, so does that mean the Vout produce will be infinite too? Then, the book says...
  33. brainbaby

    Using a low voltage supply in a class B amplifier

    Hi, friends, I have two queries. I read somewhere that 1. In class B mode higher plate efficiency (tube amp) permits the use of smaller power supplies...and 2.For low level signals a low voltage supply is used, but as the signal level increases, so a high voltage supply is utilised. Q1. what...
  34. Boltzman Oscillation

    Engineering How does this Bipolar RF Amplifier + Output Transformer circuit work?

    I am trying to create a receiver for a personal project I am working on. This is the RF amplifier that I was given by a book I am following. How does this circuit work? Usually for a BJT amplifier I find the DC bias point and then use the small signal model after I bias the circuit? I understand...
  35. paulmdrdo

    Differential amplifier common mode gain

    Summary:: Differential amplifier common mode gain derivation of forumlas I'm having a hard time deriving for equations 10-8 -10-9. I tried adding equation's 18-6 and 18-7 but cannot proceed with the derivation. I need help on this. Thank you!
  36. Boltzman Oscillation

    Engineering Variable Gain Amplifier Analysis help

    I need to find A_v, I want to relate Vin to Vout. To do this I did KVL on the major loop: $$V_{DD} = I_D*R_D + V_{SD1} - V_{SD2} - I_D*R_D$$ Since M1 = M2 then everything would cancel out and I would just get V_dd = 0 which is probably wrong. This is assuming V_sd1 = V_sd2, is that correct?
  37. C

    Engineering Calculate the max common mode voltage at the differential amplifier inputs

    Im unsure if I am on the correct track or have gone off on a tangent. Any help or guidance would be appreciated. CMRR=20log10(Adiff/Acm) 120=20log10(10^5/Acm) 120/20=log10(100,000/Acm) 6=log10(100,000/Acm) taking antilogs 1,000,000=100,000/Acm Acm=100,000/1,000,000 Acm=0.1Max amplified...
  38. paulmdrdo

    Transformer Coupled Class A amplifier Single supply

    How can Vce vary from 0 to 2Vcc? In class, I learned that it was due to Lenz Law working in the transformer and a voltage of Vcc being induced to reverse the change in Ic. However, I cannot picture this. Can someone please explain with a diagram of how this comes about in the transformer windings.
  39. B

    KCL got declined in Norton circuit of an ideal amplifier circuit

    Hi. Let's say we have a circuit like that, and we want to find the Thevenin/Norton circuit from a and b points. So for Vth, we calculate the Voc, in which we remove the 2K ohm resistor and calculate the Voc. I calculated it correctly. But I have problem in calculating the Norton current. So in...
  40. P

    Engineering How Can I Use Simetrix to Verify My Amplifier Circuit Calculations?

    I have calculated my own solution but I am struggling to work out how to use Pspice to compare my values. I am using simetrix for this - could anyone help with this part? My solution is: VGS = -IDS RS Av = Vo/Vi Vo= -gm VGS RL Vi = VGS (1+gmRS) gm= IDS/VGS so gm= IDS/-IDS RS = 1/RD = -1/100 =...
  41. M

    Engineering Find the output resistance in a amplifier (MOSFET) small-signal model

    I have to solve a problem related with an 'invented' (non-real) MOSFET working in its saturation region (amplifier). I have solved all the questions, but I'm unable to get the last one. Basically, I need to determine the output resistance of the amplifier as a function of other given 4...
  42. C

    Engineering Differential Amplifier with an Active Load

    The highlighted part is what I don't understand. Due to the gate voltage increase in M1, the current in the left branch should increase. That makes sense to me. However, he then says that the voltage at node F (in other words the drain of M1) decreases? How? Look at this plot: As current in...
  43. yalcinkaya

    LM741 Audio Amplifier Emergency

    Summary:: Hi guys! I need to make a audio amplifier circuit with LM741. I have to use only resistors and capacitors. I can't built it. Can you help me please? Hi guys! I need to make a audio amplifier circuit with LM741. I have to use only resistors and capacitors. I can't built it. Can you...
  44. W

    Engineering Looking at Operational Transconductance Amplifier (OTA) Ibias and load

    My attempt at the OTA is as follows: The simulation circuit is as follows: I've gotten this far largely due the nature of the handout and its hints. I'm struggling with understanding ibias From my understanding, there is a current mirror at the top of the OTA. This creates an infinite input...
  45. R

    Best way to match impedance between an amplifier and transducers

    I am trying to figure out the best way to match impedance values between an amplifier (50 Ohm) which powers a number of transducers (initially 50 Ohm but could change). For one transducer I have previously used a step up transformer (SUT) device between the amplifier and transducer. Now I have...
  46. wolram

    My amplifier -- why did this capacitor blow in my guitar amp?

    I have built several guitar amps, but the last one I built burned out a capacitor, can anyone think of a reson for this? it was an eloctolytic, all is working fine now I replaced it.
  47. N

    Operational Amplifier key parameters

    << Mentor Note -- new poster has been reminded to show their work on schoolwork-type problems >>
  48. hagopbul

    Find the schematic diagram for a power amplifier (for repair)

    Hello all: Doing some training in electronics repairing , and need to find some schematic diagrams for power amplifier , Google is not helping with that ,any suggestions where should I look Best Hagop