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Questions tagged [common-emitter]

A common emitter is one of three basic bipolar junction transistor (BJT) amplifier topologies. It is notorious for a high power gain. It is the only one-stage BJT amplifier topology that permits gain both in voltage and current.

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Diodes in an op-amp feedback

Consider the following circuit: (notice the 20 diodes in the feedback loop). If I analysed this correctly, the output from the common-emitter amplifier is just the input signal but inverted and with ...
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113 views

Common Emitter Amplifier design problem - seeking quick solutions updated

Looking for a quick check of solutions to the below problem. Design requirements: AC gain of G = -10 Output impedance of R = 4.7 kΩ T1 is 2N3904 npn transistor with β = 100 and base-emitter voltage ...
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95 views

Biasing in common-emitter amplifier

I'm having trouble understanding the biasing of the common-emitter amplifier as depicted below: (Image source: Electronics Tutorials - Common Emitter Amplifier) I keep reading that we should bias ...
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1answer
24 views

Modifying Transistor Properties in Proteus

I'm trying to simulate a Common Emitter circuit using Proteus. The NPN transistor which I fetched from 'DEVICE' Library has a value of VBE = 0.77V What I want is to adjust this property to 0.6V. When ...
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129 views

Understanding the basic common emitter amplifier

I'm struggling to understand intuitively this basic circuit: simulate this circuit – Schematic created using CircuitLab I know that out is \$k\cdot\mathrm{in}\$. What I'm struggling with is to ...
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28 views

Where to find details of dimensions and doping of a typical bjt

I have been searching for dimensions and doping levels of base, emitter and collector for a typical bipolar junction transistor presently in use. I have tried searching on internet and seen datasheets ...
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109 views

Is base-emitter voltage of BJT transistor (common emitter configuration) constant?

For sillicon the value of Vbe is approximately 0.7 V. So why is the input characteristics of such a transistor like this Why not a straight vertical line. Or is this curve plotted for I Vs Vbb. I ...
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44 views

Spike in RTL Inverter

I do not understand the cause of this spike which can be observed in an RTL inverter (but also in a CMOS inverter). In the following image it is the peak at 10 mS (I have considered as input a signal ...
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71 views

Common Emitter Stage BJT Amplifier with Early Effect Inclusion

How can I find Rin, Rout and Gm parameters of a BJT amplifier in common emitter stage without neglecting Early Effect? We have such homework and I couldn't find the exact same example in Behzad ...
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96 views

BJT amplifier design with input resistance, output resistance, and open-loop gain requirements

so currently i'm designing a BJT Amplifier with these requirements: Open-loop gain = 35 dB Input resistance = 600 Ohm Output resistance = 200 Ohm Another thing is the only BJTs I can use have hFE of ...
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56 views

Behaviour of Voltage on Base in a fixed BIAS Common Emitter Amplifier

I'm having some trouble understanding the behaviour of the basic common emitter fixed bias amplifier. I've been looking at this for awhile now and I'm starting to think there is a foundational ...
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37 views

CE Amplifier Small-Signal Equivalent Circuit model confusion

The following CE Amplifier Small-Signal Equivalent Circuit and nodal equations are from this site. I'm completely lost how they form the above KCL Equations for the nodes B, C and D. For example, ...
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78 views

Trying to plot input and output resistance for a single BJT in LTspice

I'm trying to plot a single NPN transistors's own input and output resistances in common emitter configuration looking into the base from input and emitter. I showed below with arrows that the plot I'...
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58 views

Confusion in setting the bias point of an amplifier

I have a textbook that details the designing process of a common emitter BJT amplifier. When designing the biasing point, the text says to set the bias collector current so that half of the supply ...
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95 views

Why are both bias resistors considered parallel in a common emitter amplifier?

When calculating the input impedance of a voltage divider biased BJT common emitter amplifier, we calculate the parallel resistance of the bias resistors and the emitter resistance. But why do we ...
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38 views

What is the gain of a common-emitter stage with base resistance and emitter degeneration considering early effect?

Hi so I have the gain for the circuit on the left without considering early effect as \$\ A_V = -\frac{R_c}{\frac{1}{g_m}+R_E+\frac{R_B}{β+1}}\$ How do I get the gain for the same circuit when ...
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261 views

Why the input resistance of a common emitter amplifier is like this?

I am trying to find the input resistance of this BJ common-emitter amplifier: I replace the transistor with the hybrid-pi model It appears clear to me that the input impedance will be \$ R_{in} =...
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302 views

Common emitter amplifier gain with load resistor?

I have a problem I am working on where I have to find the voltage gain of the following circuit with a dc collector current of 0.3mA. My attempt at a solution involved using the formula A=-(RcIc)/Vt ...
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1answer
87 views

Calculating grounded emitter amplifer distortion (Art of Electronics 3rd Ed.)

Referring to section 2.3.4 A1 (pages 94-95) of the Art of Electronics 3rd Ed., I'm having difficulty understanding how to calculate distortion of a grounded emitter amplifier. The book says: ...
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50 views

What happens to the low cut off frequency when replaced with a larger bypass capacitor?

When the emitter capacitance is increased to 100 microfarads. What would happen to the low frequency cut off of this amplifier?
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1answer
64 views

What is the ouput of this common emitter amplifier? [closed]

I need to know the output of this common emmitter amplifier circuit. I was wondering if anyone knows what the output of this circuit drawing would be I ran this through the Falstad simulator and it's ...
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78 views

For MMBT2222; How to get hfe value to calcluate minimum base current to drive transistor in Saturation?

If my collector current VCC = 3.3V & Ic = 31.82uA then how to calculate minimum base current is required put transistor in saturation mode? Depending on it I will calculate base series resistor ...
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Charasteristic curves for a transistor working in a common emitter configuration

Configuration According to my text book, When we use a transistor as an amplifier, there generally 2 resistors, one is input resister(R in) and the other is output resister(R out). Normally ...
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264 views

Voltage gain of common emitter amplifiers with negative feedback

Im trying to make some fuzz pedals for guitar using a single transistor. The one on the right is as far as i understand a common emitter amplifier with negative feedback, I somehow can't find anything ...
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232 views

How can I set the quiescent current for a grounded-emitter amplifier?

I'm currently learning about common-emitter amplifiers in AoE3. I learned how to set the quiescent current for an emitter-degenerated amplifier. I simply choose \$V_E\$ and \$R_E\$ such that \$I_E = ...
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67 views

Voltage gain of common emitter amplifier

I'm posting this question just to be sure I'm understanding this correctly. I want to estimate the voltage gain of the following common emitter amplifier either as \$A_v=-4.7\$ or \$A_v=-145\$. It'...
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300 views

Why collector current is small in value in saturation mode?

Why is the collector current smaller in value when a transistor is in saturation mode of operation? My guess is that although both the junctions are forward biased, the (forward) currents are '...
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414 views

How to derive the precise gain of an NPN common emitter amplifier without emitter degeneration?

As a self imposed exercise, I tried to derive the complete expression of gain in a common emitter amplifier without emitter degeneration. I mean by "complete" that it also takes into account the ...
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218 views

Common emitter circuit - can't understand negative feedback

I have a problem with understanding how does the negative feedback of this circuit work. In all books that I read it is said that "with the rise of temperature, collector current increases". Why is ...
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1answer
330 views

What causes amplitude clipping of single stage CE BJT amplifier with a bypass capacitor?

Where is a single stage CE BJT amplifier with a bypass capacitor supposed to clip with a normal 4-resistor biasing circuit? Like I seem to be able to get the upper peak of the output voltage all the ...
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2answers
135 views

What is the impedance of this Common Emitter transistor

I see this question on EE but the other question is slightly different of what I am asking. Suppose this circuit: Suppose I will add a capacitor to the input but I need to calculate the input ...
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4answers
108 views

Why can't my BJT common emitter trigger the pin interrupt of an MCU?

I'm trying to build a noise detector that gets triggered by pretty much all audible noises, provided that they are loud enough. The schematic design is as follows: simulate this circuit – ...
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108 views

Common emitter: maximize effective voltage gain

My homework is to design npn common emitter amplifier, with minimum output aplitude=5V, powered by +26V and -20V with generator resistance=40kOhm and output resistance=10kOhm. I have calculated ...
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477 views

Calculate Thevenin voltage in a Common Emitter Circuit

I am confused on how to proceed with the above problem. I have solved many problems on thevenin voltage but never faced one involving BJT. Please help me with this problem. EDIT: I have 2 approaches ...
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557 views

What is a common-emitter bjt push-pull output stage?

My professor mentioned it briefly in class, and I've been googling it and all I find is the CC output stage. Can anyone show me a picture of this configuration and maybe describe how it works? Can you ...
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1answer
109 views

Common Emitter, can't understand how collector current is found

So there is this common emitter transistor and it says Ic = (Vcc-Vce)/ RL, what I'm not understanding is why Ve is totally ignored, I thought Ic = (Vcc-Vc)/RL. How come the Emitter resistor is totally ...
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134 views

Identifying the configuration of transisitors

I have been handed the diagram below, as part of an introduction to transistors. I am having a hard time finding out what type of configuration it is, therefore making it even harder for me to find ...
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220 views

Why BJT BE voltage allows to avoid distortions

In Common-Emitter amplifier the BE voltage is set near 0.7V but we apply both positive and negative swings to BJT and there is no distortion on output but the signal will be 0.7V+signal_value and 0.7V-...
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719 views

Common Emitter Amplifier Voltage Gain

I'm trying to design a common-emitter amplifier with a gain of 25. I seem to have gotten the correct gain by guessing with my resistor values. Can anyone tell me how to calculate resistor values and ...
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91 views

CE transistor curves

I've created the following simulation on LTSpice and I'm running a DC sweep for V1, I1: .dc V1 0 5 5m I1 0 100u 10u. After the simulation is finished, I get those two graphs for \$ V_c=f(V_b)\$ and \$...
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114 views

Can anyone make sense of my electronics instructor's common emitter design?

I think that I need to give a little back story, but I will try to make it short enough as possible. I have a 2 year degree that I describe as half hardware/ half software. What I mean by that is half ...
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555 views

Dual Feedback Transistor Biasing a Common Emitter Amplifier

I was reviewing/following a tutorial describing the pros/cons of various transistor base biasing configurations. Configuration #4 is shown above. Resistor Rb2 was added to what was previously ...
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3answers
190 views

Common-Emitter Behavior

I built circuit shown bellow (NPN BJT): simulate this circuit – Schematic created using CircuitLab Everything worked normal as it should (except of unwanted distortion). There is that one ...
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1answer
308 views

common emitter amplifier output distortion

why the output of the Amplifier is distorted? the input from the function generator is 1 Vp the amplifier is baised at collector voltage of 4.5 V the frequency of the input signal is 1 khz the ...
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2answers
808 views

current mirror as active load in common emitter amplifier

Could someone help to analyse the circuit above, which is a single common emitter amplifier. And for the purpose of larger voltage gain, a current mirror building block is applied as active load. But ...
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1answer
140 views

CE amplifier circuit gives output voltage that is not completely out of phase

This is the circuit that I have constructed But it fails to give the output voltage that is completely inverted (out of phase) Can anyone show me whats wrong with the circuit?
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1answer
279 views

BJT Emitter Degeneration Rπ

I am a bit confused about this differential base-emitter resistance. I has been said that r_pi doesn't have much influence on small signal input impedance, when CE with emitter degeneration is used. ...
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433 views

Collector current for common-emitter audio amplifier

Looking at building an audio amplifier; many good example circuits and example tutorials based on the below simple common emitter circuit. All of them I have found so far help to size the biasing ...
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463 views

Importance of Common-Emitter Input & Output h-parameters

Speaking for NPN Bipolar transistor: In many practical examples parallel resistance of base-emitter junction (aka hie) and finite collector-emitter parallel resistance resistance (aka hoe) are ...
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2answers
355 views

Two-Stage Common Emitter Amplifier Is Clipping Unexpectedly

I've been reading about multistage common emitter/source amplifiers and have decided to test some high-gain designs with PSPICE. One design has me very confused and I was wondering if someone could ...