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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How does the common emitter configuration offer higher output impedance?

I know that the base-collector region is reverse biased and because of that it offers high resistance but it is the resistance due to biasing. In a video, the person was explaining the hybrid-pi model ...
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Common emitter amplifier with low impedance

The following schematic shows a common emitter amplifier driving a resistive load. The common emitter has a high output impedance, is it possible to use the amplification achieved with the common ...
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How to calculate the output resistance of the CE amplifier, which has only a coil in its collector?

In order to be able to match the impedance, it is necessary to know the output resistance of the amplifier. In radio frequency amplifier circuits, there is usually a coil in the collector instead of a ...
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Wrong calculation of collector current

There is a transistor circuit which I am DC analysing. I did KVL to find base current. -5 + Ib.10k + Vbe(0.7V) = 0 Ib = 0.43mA Hfe of NPN transistor is 100. Ic = hfe.IB, Ic = 0.43mA*100 Ic = 43mA But ...
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Common-Emitter Analysis

I am making an error in the analysis of the above circuit. $$i_i=i_b \implies v_1=i_b\cdot r_{\pi}$$ So the value of $$g_m v_1 = g_m\cdot r_{\pi}i _b= \beta i_b$$ But, this is the same current (\$i_c =...
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Why does my transistor explode in a simulator?

I'm new to electronics and I can't identify the reason why my transistor explodes when I simulate it. I am simulating a simple common emitter amplifier with a power supply of 12 volts.
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Designing the first stage (common emitter) of an amplifier that will drive an 8 ohm speaker

I have to design an amplifier (can be one stage or multiple thought I am thinking multiple) that will drive an 8-ohm speaker and have a gain of at least 10 V/V (about 20 dB) given Vcc = 9 V. It also ...
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Why is the cut off voltage on the AC load line lower?

I know the AC loadline is steeper because the load resistance \$r_c = R_C||R_L\$ is low, but a low resistance DOESN'T shift the cutoff voltage. That is because when the BJT is OFF, all the supply ...
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How to find the output impedance for the unbypassed Common-Emitter Emitter bias configuration when ro presents?

I have found an equation in the book of Boylestad, but that equation is not matching with the equation which one gave solve for this type of question previously. $$Z_o=R_c \parallel \left[r_o+ \frac{\...
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2 answers
148 views

Common emitter amplifier - calculate Q-point?

I am currently studying the common emitter amplifier and I am getting some nasty clipping in the output. So what I am trying to do is to figure out how I can calculate the highest and lowest output ...
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171 views

How to increase CE amplifier gain to 12?

The gain needs to be increased to 12, currently it is at 10 but I cannot seem to increase this any more. The circuit topology cannot change, but the component values can - except R4, the 56 kΩ ...
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Input selectivity for a RF receiver pre-amp

In his answer to my question about common emitter amplifiers, @glen_geek commented that the RF receiver pre-amp I used as an example (shown in Figure 1) was "too simple" and that "any ...
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How to design an amplitude modulator with common-emitter amplifier circuit?

I am facing a problem on how to design an amplitude modulator using a common-emitter amplifier circuit. I am asked to use a carrier frequency of 50MHz and an input signal of 1kHz to 14kHz. In order to ...
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3 answers
225 views

How to fix when the amplitude modulated signal reaches the peak, the bottom follows too?

I have designed an amplitude modulation circuit for my school project. I realised that the amplitude modulation can be achieved by just adding a message signal at the emitter part to vary the gain of ...
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Cascade BJT amplifiers gain calculation

I've been trying to cascade BJT amplifier to get a gain of 800. My input is 10 mV, and I want an output of 8 V. My question is, how does the gain of common emitter amplifiers work? I've created a ...
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What is the desired total low frequency response for a common emitter amplifier? [closed]

For a common emitter the total low frequency response is different, depending on the values of input, output and bypass capacitors. Three separate cutoff frequencies: One cutoff frequency when all ...
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Why is the voltage drop across the collector emitter junction of common emitter configuration the output voltage instead of that of load resistance?

This question is connected to the link. Why are base current and emitter current the input current in common emitter and common base configurations respectively? Is voltage drop across the base-...
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Why are base current and emitter current the input current in common emitter and common base configurations respectively?

I am a high school student learning about semiconductors (diodes and transistors). I have been facing a lot of problems to understand the configurations of BJTs and the simplest amplifier circuit. ...
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Which value of beta to use in common emitter amplifier circuit calculation

I have this circuit. In the data sheet, I found values for the DC current gain (beta.) Which value for beta do I use in this common emitter amplifier circuit? Is my method to get the base, emitter and ...
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Transistor amplifier design

I need to design a common emitter amplifier for my next electronics laboratory. Specifications are the following: 1 mA of collector current Load resistance of 1k ohms Voltage gain of 10 For 1mA, $$ ...
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1 answer
188 views

BJT current gain: Relation of SPICE parameter BF to beta

As far as I understand, the BJT (bipolar junction transistor) DC forward current gain in common emitter configuration is given by It seems those symbols all used to describe the same thing (correct ...
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Why is there a minus on the voltage gain of a common emitter?

In a common emitter amplifier with \$h_{re}\$ and \$h_{oe}\$ unimportant, and a load $$R_{CL} = R_C//R_L$$ I'm studying the gain voltage $$ A_v = \frac{v_{ce}}{v_g} = \frac{v_{ce}}{v_{be}}$$ So $$i_c =...
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Discrepancy in increasing AC voltage gain of a Common Emitter Amplifier

This is kind of a follow-up question to Simulation on LTSpice not matching with Calculations at Q-point , which I had asked previously. Here is the circuit again: The new components added are \$R9=94\...
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Simulation on LTSpice not matching with Calculations at Q-point

Here is a circuit- It has 2 parts, the first part generates a triangular waveform with pk-pk voltage of \$1.2V\$ approx. The second part is a CE amplifier with intended circuit gain of \$-10\$. The ...
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Av Ltspice value for Common Emmiter amplifier is not the calculated one

I am designing a common emitter amplifier with a total gain of magnitude 5. I biased the transistor at the Q point I wanted: IcQ = 40mA (checked with LTSPICE). The expression i found for the gain of ...
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2 votes
1 answer
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What sort of iron rod should I use in a magnetostriction oscillator?

I'm trying to make a magnetostriction oscillator at home. Here is the circuit diagram: 1 DC Power Supply 2 Ferromagnetic Core (Iron) 3 NPN Bipolar Junction Transistor (2N2222) 4 Capacitor C 5 Primary ...
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2 votes
4 answers
317 views

What is the small signal gain for this circuit?

The question looked easy at the first sight. I found the quiescent current through the BJTs. I can say that |Vbe| = 0.7 V for both BJTs. Therefore, current through 1 kΩ below Q1 = 2 mA. Similarly, ...
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3 answers
144 views

How are desired specs decided upon in a common emitter amplifier circuit? (beginner)

I have been reading up on amplifier circuits recently out of curiosity and would like to attempt designing my own. However, I would first like to understand how various amplifier specifications are ...
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Improving grounded emitter amplifier with collector-to-base bias

According to books, this simple grounded-emitter amplifier has some shortcomings. For example, 1) the d.c. operating point is unstable. 2) since the intrinsic resistance of emitter, \$r_\text{e}\$, ...
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calculating power (with no signal) in common emitter amplifier

I am reading through some school notes on audio amplifiers and have come to the section on calculating power when there is no signal present. My own calculations disagree with the answer given (...
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How can I find the VBE of a common-emitter amplifier?

I have a common-emitter circuit as above. I need to find the value of Vbe and IC. The picture below is the equivalent large-DC analysis of the circuit. Applying KVl Ic = (VTH - VBE)/((1/B)RTH+(B+1/B)...
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Applying Kirchhoff's voltage law to a bipolar junction transistor [closed]

I am new to the field of electrical engineering. As a part of my curriculum, I am required to study about bipolar junction transistors and their configurations. Question: In the active common emitter ...
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2 answers
140 views

Why isn't my common emitter amplifier working properly?

I simulated this common emitter amplifier in LTSpice: However, instead of an amplified sine wave, the voltage at the output looks like this: Would someone be able to explain why this is happening? ...
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7 votes
3 answers
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Is it possible to reduce distortion in a common emitter amplifier?

I am designing a common emitter amplifier for educational purposes. I work in a different engineering field so please bear with me. The gain of the circuit is around 26 (enough for my purpose), but ...
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Calculate -3db point in low pass inverting transistor audio amplifier

What I am trying to do: I am looking to find the \$ -3dB \$ frequency for my common emitter transistor amplifier with a capacitor in the feedback loop. I have somewhat of an idea, but I wanted someone ...
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Difference between CE, CB and CC transistor configurations

In the different configurations of transistors, namely Common Base (CB), Common Emitter (CE) and Common Collector (CC), I am asked about the basic difference. So can I say that the basic difference is ...
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CE Colpitts not oscillating

There seems to be a few questions around this but none of the suggestions solved the issue for me. I apologize for the long question but I would like to present my thinking and everything I tried. ...
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Input & Output Impedances of Common Emitter BJT Amplifier

I want to study about "finding Input & Output Impedances of Common Emitter BJT Amplifier" However, I could not find a decent source & document about it. Could someone supply me with ...
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Input and Output Impedance of the Common Emitter Amplifier

I just have solved one of the bjt common emitter question below. However, I'm curious that how can I additionally find those things below: 1) Input and Output Impedance 2) AC Gain Here is the example ...
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Why is the voltage gain in the simulator so different from the expected gain?

simulate this circuit – Schematic created using CircuitLab I was watching this youtube video for an explanation of voltage gain. Just for verification, is the formula for voltage gain also ...
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3 answers
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Is a base resistor always needed in a single transistor inverter circuit?

For the circuit shown, I'm trying to figure out if I need a base resistor or not. What I'm looking to accomplish is a simple logic inverter to hold a power amp's active low shutdown at logic low ...
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2 answers
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Why is there a resistor in this circuit?

Why there is a 220 ohm resistor in this circuit? Can't we just connect the thermistor directly to the base of transistor?
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8 votes
3 answers
709 views

Irregular common emitter amplifier design

Would anyone know of any merits (or demerits) to the common emitter amplifier represented in Figure 1 in comparison to one of a regular pattern (Figure 2)? Thanks. (The 'DS548' transistor in Figure 1 ...
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How does a two input transistor AND gate work?

I'm trying to self study electronics. I started reading a book on digital electronics and I got stuck on the first chapter. It's about the logic gate circuit. There is a two input AND gate circuit and ...
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How do I increase the voltage gain of a Common Emitter + Common Collector without distortion in Vo?

I started with R1 and R2 half of what they were now, and with R_C = 5k. This had a gain of about 11, I managed to increase that by increasing R_C, but it seems to be plateauing when I start to get ...
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6 answers
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What is the purpose of the emitter resistor in a common emitter amplifier?

I'm struggling to understand the purpose of the resistor circled in red, I know it has something to do with DC biasing and the feedback on the circuit (as the capacitor will cause AC bypass). But I'm ...
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How to calculate bias resistor values to drive IR diode

I'm creating a circuit to do communications via a digital serial infrared link. My requirements are for the link to support relatively high speeds (maximum serial bit rate is 4,000,000 bps or 4Mbps) ...
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Modifying a CE transistor Amp to a Single Ended Class B Amp

I've designed the above amplifier to give an Av=10 and be mid point bias. I simulated it and it's all working well. But I need to modify the bias (so only changing resistor values, not adding or ...
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4 votes
2 answers
581 views

Shorting NPN transistor base to ground

What is the normal convention(safe and reliable), should one connect NPN transistor base to ground or should a resistor be used? My logic tells me that in common emitter mode, shorting base to ground ...
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Correct design of Colpitts oscillator

I have been watching this video and when it is designing the colpitts oscillator it doesn't add a base resistor. I am thinking that is wrong because the BJT will saturate since the guy sets a base ...
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