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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46 views

Bootstrapping. Common emitter amplifier

How to properly choose bootstrap capacitor and resistor in the common-emitter amplifier circuit, if we know that the circuit should have a low-frequency 3dB point at 100 Hz? Here is the schematic. : ...
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102 views

Art of Electronics Ex.2.20 Series negative feedback amplifier

Here is the exercise followed by a schematic: Applying the techniques we used earlier, one can show that G(open loop) ≈ 200, loop gain ≈ 20, Zout(open loop) ≈10k, Zout(closed loop) ≈ 500Ω, and ...
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54 views

Is this the correct AC analysis of the following circuit?

If I have the following circuit simulate this circuit – Schematic created using CircuitLab Is this AC analysis correct? I am not sure if I should add the R4 resistor in series with the re ...
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114 views

When doing the DC analysis of a common emitter amplifier, why can we disconnect the parts involving capacitors?

I don't understand why the components involving the bypass capacitors and the coupling capacitors need to "disappear" when we are doing the DC analysis.
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Transfer Function of two Common Emitters

I'm sorry about the pictures and used circuitlab. I am dealing with a circuit that has two common emitter transistors. Until now I was only dealing with a circuit that that is common emitter. This ...
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37 views

Amplifier \$I_c\$, \$V_{ce}\$ operating range

In the 10th edition of Electronic Devices from Thomas L. Floyd Example 6-1 provides a way to find the AC model output signal operating range based on the following circuit. I'd like to ask for a ...
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70 views

What if I switch the place of the load in a common emitter NPN transistor circuit?

As you can see in the picture, there's an NPN transistor in a common emitter configuration. In the first configuration, the load is placed between the collector pin and Vcc, and it is the most ...
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131 views

Why output signal is not symmetrical? What to do?

I am trying to design a 2-stage amplifiers with first stage C.E with PNP transistor and second C.C with NPN transistor. The amplifier is supposed to have a gain more that 40. After designing the ...
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65 views

Would a capacitor between base and emitter make relay amplifier less noisy?

I have a single transistor relay amplifier driven by GPIO output of Raspberry PI. The amplifier works reliably and is not causing any immediate problems. Still, if I leave the relay flipping on/off ...
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1answer
63 views

How to increase output voltage of an op amp well above the supply voltage

I have a circuit which produces a (not high speed) signal between 0 and 9 volts with an adjustable slope, and I would like to increase this output voltage to between 0 and 200 volts, which keeping it ...
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745 views

Emitter resistor and biasing voltage

In many articles regarding transistor biasing I see a circuit like below and I don't really get what is the point of biasing like this WITHOUT emitter resistor Re? When emitter branch is connected ...
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1answer
80 views

Miller compensation capacitor sizing

How can I size the circled capacitor in order to get rid of the peaking? Is there some formula? Cheers
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2answers
81 views

Calculation of base current and what decides the current through collector-emitter branch

I have the below circuit. Its not a homework material. I am understanding how to analyze the transistor circuits. Below are my questions while trying to analyze : If I am given the below circuit, ...
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1answer
59 views

Coupling capacitors in a CE amplifier

I know that those C2 and C3 are used to isolate DC from the input and output. Capacitors are always open to DC(w=0) and since the equivalent impedance of a capacitor can be expressed as 1/jwc in ...
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38 views

Cutoff frequency of class A common-emitter amplifier

I'm trying to understand the operation of a class A common-emitter amplifier, but I'm struggling to understand how the equivalent resistance for the cutoff frequency of C1 is determined. I also can't ...
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1answer
137 views

Choosing Collector Current for Transistor Amplifer

I see in the guides to standard Bipolar Transistor circuits (emitter-follower, common emitter amplifier), they always say: Choose a quiescent current of 1mA. How is this value chosen? I look at the ...
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58 views

Necessity of beta in common emitter design

I'm thinking about a common emitter circuit like this one: Initial assumption: If the base current is very small compared to the emitter current, then the collector and emitter currents are ...
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39 views

Examples of Common Emitter Circuits [duplicate]

I want to practice more bipolar transistor, more specific Common Emitters. Can someone give me any source where there are exercises with solutions of Common Emitter Circuits . i just want to go ...
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Why do germanium transistors and silicon transistors have different conditions for cutoff region in common emitter configuration?

The textbook I currently read defines cut-off for PNP germanium transistors like this: For germanium transistors, however, cutoff for switching purposes will be defined as those conditions that ...
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50 views

2VCC in a BJT C.E. amplifier

It is known that it is possible to get 2Vcc output voltage in a BJT Common Emitter amplifier by using an RF Choke (instead of a simple resistor) connected to the collector. Precisely, we will get at ...
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1answer
97 views

Designing 2-stage BJT CE class-A voltage pre-amplifier with specified goals and without global NFB

BJT CE Class-A Voltage Pre-Amplifier Suppose a design requirement limits the selection choices to the following class-A BJT common emitter stage topologies. No global NFB is permitted. Only local NFB ...
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4answers
590 views

Class A Amplifier Design: Emitter Resistance Voltage Drop

I am trying to understand the design principles of Class A amplifiers, primarily for audio purposes. I have read several times that "the voltage drop across the emitter resistor should be in the ...
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4answers
441 views

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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1answer
287 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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2answers
152 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
345 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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207 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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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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375 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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2answers
61 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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1answer
153 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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1answer
141 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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3answers
89 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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1answer
100 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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172 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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112 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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2answers
154 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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1answer
520 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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2answers
444 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
134 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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52 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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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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170 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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1answer
45 views

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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348 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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366 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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71 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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672 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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503 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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284 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 ...