What is Gain: Definition and 416 Discussions

In electronics, gain is a measure of the ability of a two-port circuit (often an amplifier) to increase the power or amplitude of a signal from the input to the output port by adding energy converted from some power supply to the signal. It is usually defined as the mean ratio of the signal amplitude or power at the output port to the amplitude or power at the input port. It is often expressed using the logarithmic decibel (dB) units ("dB gain"). A gain greater than one (greater than zero dB), that is amplification, is the defining property of an active component or circuit, while a passive circuit will have a gain of less than one.The term gain alone is ambiguous, and can refer to the ratio of output to input voltage (voltage gain), current (current gain) or electric power (power gain). In the field of audio and general purpose amplifiers, especially operational amplifiers, the term usually refers to voltage gain, but in radio frequency amplifiers it usually refers to power gain. Furthermore, the term gain is also applied in systems such as sensors where the input and output have different units; in such cases the gain units must be specified, as in "5 microvolts per photon" for the responsivity of a photosensor. The "gain" of a bipolar transistor normally refers to forward current transfer ratio, either hFE ("beta", the static ratio of Ic divided by Ib at some operating point), or sometimes hfe (the small-signal current gain, the slope of the graph of Ic against Ib at a point).
The gain of an electronic device or circuit generally varies with the frequency of the applied signal. Unless otherwise stated, the term refers to the gain for frequencies in the passband, the intended operating frequency range of the equipment.
The term gain has a different meaning in antenna design; antenna gain is the ratio of radiation intensity from a directional antenna to





{\displaystyle P_{\text{in}}/4\pi }
(mean radiation intensity from a lossless antenna).

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  1. S

    I Can gravitational waves gain energy in an expanding FRW spacetime?

    I was reading this paper (*Green's functions for gravitational waves in FRW spacetimes:* [https://arxiv.org/abs/gr-qc/9309025](https://arxiv.org/abs/gr-qc/9309025)) and I had a specific question about one statement in the paper that I would like to ask: At page 6, the author says that...
  2. A

    Vintage EEG Gain compared to modern voltmeter

    I got from my drawer last night a vintage Brainmaster 2E I bought late 1990s that I used only a few times during that period. It has serial port at back. I don't know if it will work using a USB to serial port adapter connected to my laptop. Do you think it will work? My question concerns the...
  3. L

    I Do objects gain mass while approaching light speed?

    I watched a fermilab video claiming objects don't actually gain mass as they approach light speed. Is that true? What keeps things of mass from reaching the speed of light or beyond? I assume matter doesn't accumulate higgs-bosons while in motion?
  4. amgc63

    Please help me understand antenna power gain…

    Question; Given that a dipole antenna has directional gain of 2, calculate the power gain in Dbi? Answer; Power gain = 10 log (x/y), where y =1 Power gain = 10 log (2/1) = 3dbi My question is….how come y = 1?? Thanks in advance
  5. jaumzaum

    I Radio waves and height gain in fading zones

    Hello Guys! I'm studying radio waves and I can't understand the following: Radio waves propagates through Earths surface as a ground waves, line-of-sight waves or skywaves. There is a phenomenon that occurs with line-of-sight waves (and maybe with ground waves?) known as height gain, in which...
  6. 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: $$-v_i-v_{DS}+v_o=0$$...
  7. ergospherical

    Justifying the peak closed loop gain of an op-amp circuit

    I'm just looking at a Bode plot of log(gain) vs log(frequency) for a an amplifier circuit. I'm trying to figure out whether I'm expecting to see a resonance in the gain at the frequency where I measured one. How could I, in principle, work out theoretically where the peak gain should occur - is...
  8. song youngill

    Engineering How can I find DC gain via AC simulation in LTspice

    I use this netlist and simulation result came out as shown. I need to find the dc gain here and circuit diagram, but I'm not sure how. I would be very grateful if you could give me the answer.
  9. P

    Engineering Designing an Integrator Circuit with Given Absolute Gain

    For the integrator circuit, I can design the cutoff frequency and the 0dB frequency as required. Using Laplace transforms, the gain is around ##-\frac{1}{sR1C}##, where s is the complex impedance parameter. But, how do I maintain the absolute value of this gain at 10 for the whole band pass for...
  10. P

    Engineering Analyzing the output impedance and open loop gain of a IC-741 Op-Amp

    Here is the internal circuit of the 741 Op-Amp - Looking at the output stage, the output impedance seems to be the series combination of ##25 \Omega## and ##50 \Omega##, that is ##75 \Omega##. Is this a qualitative explanation enough to justify the output impedance, or am I wrong somewhere and...
  11. C

    When to have only voltage gain in an oscillator

    What I already know In general, power gain is desirable for an oscillator in order to make up for the losses and then feedback that gain (amplified signal) into the oscillator for it to keep oscillating. Voltage gain is not generally used for oscillators. What I want to know Since power gain is...
  12. E

    This op amp does not have gain?

    Had this as a question from a class mate. This op amp should not have any gain in the DC or AC circuit. The coupling cap blocks DC and has no reference to get gain, while the AC needs a cap in the feedback loop to get gain. Is that correct? Oh, this is supposed to be in the inverting configuration.
  13. Wrichik Basu

    Gain limiter circuit in LTspice - current flowing in wrong direction

    This is one more thread in my quest to learn simulations in LTspice. I am trying to simulate the gain limiter network shown in this video. A snapshot of the video is available for quick reference: My schematic in LTspice is shown below: For the simulation, I am using DC sweep on voltage...
  14. PainterGuy

    Engineering State feedback gain for observer/estimator

    For the state equations given above calculate state feedback gain k so that the state feedback system has -1 and -2 as its poles. Then, find TF from r to y for the given state feedback system. Then create a 2 dimensional estimator where the poles of estimator are -2±2j. Finally calculate TF from...
  15. 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?
  16. garthenar

    Engineering W0 = 1/RC? Transfer Functions and Bode Plots

    Here is the example and solution in full. I have circled where I'm at and highlighted the part that's tripping me up. I managed to get... and getting everything in terms of the angular frequency seems to be critical for getting the plots for the Frequency Response. I checked my notes on RC...
  17. MarkNormand99

    Finding the gain coefficient at line centre for a HeNe Laser

    I have found the value for the full width at half maximum line profile width , I know the the density of the upper lasing state for the helium neon laser is 10^18 m−3, and I am assuming I have to use dN_2/dt = -A_21N_2, which I can turn into N_2(t)=N_2(t=0)exp(-A_21*t), and I have calculated...
  18. M

    Engineering Link Budget Antenna: use of effective aperture and the gain in a problem

    Hi, I was just attempting this problem and was confused about the calculation process involved. Context: In earlier parts of the question, we calculate the gain ## G ## and effective aperture ## A ## for the parabolic antennae. My Attempt: We are given the power at the output ## x ## in Watts...
  19. W

    A Feature Selection, Information Gain and Information Entropy

    Sorry for being fuzzy here, I started reading a small paper and I am a bit confused. These are some loose notes without sources or refs. Say we start with a collection F of features we want to trim into a smaller set F' of features through information gain and entropy (where we are using the...
  20. 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!
  21. 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?
  22. Boltzman Oscillation

    Engineering How can I find the open loop voltage gain of this opamp?

    The open loop voltage gain is given as : $$ u(s) = \frac{u_o}{1+\frac{s}{w_o}} = \frac{100}{1 + \frac{s}{40}}$$ Where u_o is the d.c. voltage gain and w_o is the pole. The op amp that is given is: And I am told to use the non ideal op amp model as follows: Well my guess is that I can find the...
  23. J

    Solar heat gain on a typical solar cell

    what will be the joules per meter using thermal gain and wattage gain from a solar cell if the cell is in an insulative vacuum not counting the thermal degredation of 25% for wattage loss due to heat gain
  24. U

    Laser gain and the saturation effects

    Hello, I study laser physics, using "Laser Physics" by Eberly and Milloni. I am confused regarding the notion of gain and the saturation effect. According to the book, the gain is defined as ## g(v) = \dfrac{g_o(v)}{1+I_v/I^{sat}_{v}} ## where ## I^{sat}_{v}## is the saturation intensity and...
  25. X

    Higher Gain for PMT: Does it Really Improve SNR?

    Empirically, photomultiplier tube (PMT) is said to present better signal-to-noise ratio (SNR) than avalanche photodiode(APD). Some materials say that it is attributed to the higher gain and lower dark current of PMT. The benefit of higher gain is confusive for me, since I suppose that noise (of...
  26. C

    I How do I calculate the expected Gain?

    I am doing an experiment in electronics with AC RLC circuits, But there are a few things about what I need to do that I don't understand. First: While I know in the circuit diagram we include the internal resistance of the Inductor in series, but I don't know why we include it in series rather...
  27. C

    How do I gain creative experience in engineering?

    Summary: (undergrad student) What is something I can do this summer to develop my creative instinct in engineering? Hey everyone! I am currently an undergrad freshman studying mechanical engineering. I love the courses and I understand the scientific concepts, but I know that engineering is a...
  28. greenrichy

    Reasons for a gain of momentum during a collision

    I've come up with the following causes: - air resistance - parallax - during the collision, some of the kinetic energy gets converted into thermal energy. - invisible deformations But I'm not sure which would be the biggest effect on the total momentum change. Are there any other reasons that...
  29. Terrycho

    (Bipolar Junction Transistor) The Current Gain of Common Base Amplifier

    Everything is okay besides the current gain of this circuit, which is "g" there The formula of current gain is I_out/I_in If I call the current flows to R_e I_2, according to KCL, the following formula must be satisfied. I_in + (β+1)I_b = I_2 Therefore, to know I_in, we should use the...
  30. F

    A Forecast with Fisher formalism : loss or gain of information

    In the context of a forecast, I am currently working on Fisher's formalism which is part of a more general theory, that of information. My problem applies to estimating cosmological parameters from input data with the Fisher formalism and recipes to build a Fisher matrix. The context is...
  31. Peter Alexander

    Engineering Compute the voltage gain of this bipolar junction transistor circuit

    This is the given schematic. The result should be $$A_u = \frac{R_b g_{21}}{1 + R_b g_{22}} = -50$$ and the way I wanted to tackle this problem is by stating $$A_u = \frac{-R_b i_2}{u_1} = \frac{-R_b (g_{21} u_1 + g_{22} u_2)}{u_1} = \frac{-R_b (g_{21} u_1 + g_{22} u_2)}{g_{11} u_1 + g_{12} u_2}...
  32. D

    I Compute the optical gain of a quantum well

    Summary: Search to compute gain of a quantum well. Stuck with maths or programming. Hi everyone ! For a personal project, I search to compute the optical gain occurring on a semiconductor quantum well. I have based my calculations on a paper called Investigation and comparison of optical gain...
  33. P

    How do you gain your confidence back?

    Hello! I'm currently in my Junior year of college (2nd semester) and I feel like I've lost a lot of confidence that I had prior to this semester. Before this semester, I spent a lot of time studying and doing research and while I still maintain a 4.0 cumulative GPA as a Physics and Math major...
  34. A

    B The Gain of the Inverting Amplifier and Virtual Earth....

    This is an inverting amplifier incorporating an ideal op-amp with infinite open loop gain. I have a simple question concerning the derivation of its gain (-R2/R1). The point I circled is at 0V (Virtual Earth) but then, if V+=V-, Shouldn't Vout=0 regardless of what R2 and R1 are?? What's wrong in...
  35. Boltzman Oscillation

    What is the gain error for this opamp driven by a voltage

    Homework Statement The op amp has a near ideal level 1 model with G = 5000V/V, ri = inf, ro = 0 How would I obtain the feedback function? Homework Equations I know I have to find the feedback function which is: f = - (ΔV/Vin) The Attempt at a Solution I will first drive using the...
  36. K

    Calculating controller gain in a feedback loop

    Homework Statement FIGURE 3 shows the block biagram of the control of an electric heating system. The heater is driven from a voltage-controlled power supple, the voltage V1 being derived from a potentiometer. The output temperature, θo is subject to distrubances, θd, because of changes in...
  37. Boltzman Oscillation

    Engineering Derive expressions for the voltage gain of this opamp circuit

    Homework Statement Derive the expressions for the voltage gain (Gv) of the following op amp: Homework Equations In = Ip = 0 Vp =VnThe Attempt at a Solution I can use KCL, and the fact that In and Ip are both 0, to derive the two equations, one from the top node and the other from the...
  38. A

    Voltage Gain of a common-emitter amplifier

    Hi, i have a problem with the voltage-gain of a common-emitter-amplifier. I have calculated the theoretical value of the gain given by ##G=\frac{\partial U_{a}}{\partial U_{e} } = -h_{FE} \frac{R_{c} }{R_{v} }## , which is between -13925 and -7311 for ##420\leq h_{FE} \leq 800## (given by the...
  39. J

    Maximum gain possible by sound wave focusing

    Just like a concave mirror concentrates light, it can also concentrate sound waves. Ray diagrams like the following look as if all waves converge to a single point of INFINITE power density which of course is not true, probably because of the wave nature of light or sound. What is the correct...
  40. adamaero

    Conversion gain for mixer (BJT switch)

    Homework Statement a) If this mixer is connected to a matching 50Ω resistor, what is the conversion gain? b) IIP3 (Third Order Intercept Point) is 15 dBm, what would be A1dB? c) What is P1dB?Homework Equations https://www.ece.ucsb.edu/Faculty/rodwell/Classes/ece218b/notes/Mixer1.pdf#page=9 b)...
  41. M

    Hi, how to make 2 IF from one IF amplifier circuit, to get higher gain

    Hi, i take one If amplifier, from internet and i want to make the second the same, but i don't know how to couple, of what i need to do, to get more gaing can somebody help me? here is one IF amplifier in ltspice, rename in asc, or remove only txt extesion. and what is the best to do, is for fm...
  42. C

    Is this small-signal gain correct?

    Homework Statement All MOSFETs (no JFETs) Ignore body effect. Is my gain correct? Just want to confirm. Homework EquationsThe Attempt at a Solution
  43. T

    B Brown Dwarf Mass Gain: Does Radius Increase?

    Why wouldn't a brown dwarf grow in radius if it started to gain mass?
  44. C

    Calculating Required Gain for Fifth Intermediate Amplifier

    Homework Statement FIGURE 1 shows the block diagram of a superhetrodyne radio receiver. In a test a 20 μV signal was fed from the aerial into the first stage of the receiver, a radio frequency amplifier. This signal is the passed through several stages of the receiver to eventually appear at...
  45. Cocoleia

    What is the phase margin and gain margin for this circuit?

    Homework Statement The Attempt at a Solution I am having trouble visualizing this. So I know that the phase margin is how much phase lag it would take to make -180 phase at the 0 dB gain frequency. I am just having trouble placing this on the plot. It isn't a homework question I am preparing...
  46. N

    Optimizing Phase and Gain Alignment for DF Systems at 200KHz

    Hi all I have simultaneously recorded data coming from three pre-amplifiers with same input applied to these pre-amps. After post analysis, i found that there are phase and gain differences among these outputs ( which should be zero in ideal case). I set one preamplifer output as reference and...
  47. J

    Wire size and type for gain clone type amp?

    I have constructed a gain clone type amp based on the LM3886 chip from Texas Instruments. I have wired it using some available 16 gauge stranded wire. It is powered by a centertapped 34 volt (68 volt total) transformer that is fused by a 2 amp fuse. It is working with no issues however I would...
  48. C

    Finding the magnitude of the voltage gain in dB

    Homework Statement Hi, so in a MOSFET amplifier question(a common-source amplifier in particular), we are examining the effects of the parasitic capacitances of the MOSFET when included in the small-signal model. In particular, the gain of the amplifier with these capacitances. So I derived the...
  49. PseudoQuantum

    Studying How can I gain more science knowledge over the summer?

    Hi all who view this, I am currently a high school senior and I plan to go to a community college for my first two years of college study to try and find what I would like to major in before embarking on a certain major I may not even find all that interesting later on. I love science, but my...
  50. alan123hk

    B Proof of the relation between antenna aperture and gain

    Where can I find strict mathematical proof of the relation between antenna aperture and gain which is applicable to any type of antenna ? Aeff = Gain * (lambda^2) / (4*Pi) Aeff - Antenna Effective Aperture Gain - Antenna Gain lamdda - wavelength Pi - 3.14159 Many textbooks just show the...