# 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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### Determining the zeros and poles of a common emitter amplifier

I want to determine the transfer function of the base common emitter amplifier. I don't want to neglect the impedances of the capacitors in the calculations because I want to determine the zeros and ...
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### Why should the Vce be half the value of the supply source?

For a BJT amplifier biased to operate in the active region; I think that the statement "the voltage Vce is half the value of the supply source" is incorrect. Because I know that such a thing ...
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### Do transistors "prefer" to pull current from their base or collector?

The circuit below is a simple BJT amplifier which behaves exactly as expected: If I remove the capacitive coupling and voltage divider bias and replace it with an input offset, it completely breaks ...
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1 vote
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### Why does the voltage increase when I connect this amplifier to a gate driver?

I'm trying to breadboard a simple circuit testing a TI UC3708N gate driver, which I need to drive from an AWG square wave. Since the AWG has limited amplitude (and perhaps limited current), I made ...
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### How to analyze common-emitter amplifier by reflecting base impedance to emitter?

In chapter 2 of Dr. Middlebrook's video series Technical Therapy for Analog Circuit Designers he gives 2 examples of how solving a CE amplifier by "doing the algebra on the circuit diagram" ...
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### BFU730F doesn't work on real experiment, what is wrong?

I have calculated BFU730F transistor on paper - all is ok. I have created simulation for similar transistor (BFR740 because there is no BFR730) - all is ok. I have maked shematics - it is not working. ...
297 views

### Is the resistor between the clock and the NPN needed?

I have a circuit that uses an NPN transistor inverter to invert a clock signal. The circuit calls for two resistors, a pull up and one in between the input signal. Virtually all of the circuits found ...
1 vote
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### Is LTspice AC analysis trustworthy at RF when using low impedance sources?

I'm an amateur at circuit design but I've been reading a lot and trying my best. I've edited the question to try to make the main problem more coherent and add a simple schematic and plots. My setup ...
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### Question about class A amplifiers

I am trying to understand the working principle of a simple class A amplifier. Below you can find a diagram of the inner components. I am struggling to understand why the gain $G$ is given by the ...
99 views

### Breaking "rule of thumb" for common emitter?

I'm trying to understand this common emitter amplifier that is part of the of a guitar pedal. The image is take from the ElectroSmash analysis from the Big Muff Pi . The values for R6 and R4 are ...
1 vote
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### LTspice: Troubleshooting a common emitter amplifier

This is a screenshot of a common emitter amplifier my instructor made in LTspice (everything is working fine): This is my attempt to make the same circuit (it isn't working, there's no amplification ...
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724 views

### PNP transistor not pulling up completely : what is wrong in my schematic?

I cannot seem to make the schematic below work. As you will plainly see, the idea is to use the PNP as a switching device for a PhotoMOS (TLP354x). By switching SW1, Q1's base goes to the ground ...
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1 vote
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### Emitter circuit on a breadboard

I am working on an emitter circuit that has a 2N3904 NPN transistor. I have simulated the circuit before and got the results. I am trying to build it in the lab so I can compare the results to my ...
1 vote
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### No DC offset observed in the CE amplifier circuit part

The objective is to make an audio amplifier. We have decided to make one that has four stages: a pre-amp with a gain of around 120, the next one is a CE amplifier with a gain of around 5, the third ...
1 vote
262 views

### Why am I concluding that the emitter-degenerated CE stage is unilateral?

Consider the attached small-signal diagram for an emitter-degenerated CE stage: It's been a long day so I must be making an error, but I continue to conclude that this two-port is unilateral (defined ...
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### Designing a common emitter amplifier circuit

How I calculated the resistor values: I assumed that Ic = 1mA, and β = 50.5. It is given that VDD = 5V and to design the circuit to get a gain of 10. The transistor is 2N4401 RC = VRE / Ic = (Vdd/2) /...
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### CE Amplifier problem

I am new to learning about electricity and I was trying to make a common emitter amplifier. I did some research and I tried to make the circuit. The circuit amplified the signal but the signal was not ...
3k views

### Why are only 3 of 6 single-transistor amplifier configurations useful?

Almost any analog design book or course I have ever seen starts by introducing the three basic single-transistor stages. For example, in a bipolar technology these are the common-emitter, common-base, ...
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1 vote
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### NPN Transistor Base Current Calculation from Beta, Vth, and Rth

In this answered question regarding a common emitter NPN Transistor.... NPN Transistor common emitter calculation I am struggling to understand the section "Assuming Active Mode" ...
171 views

### Problems with choosing resistors for a common emitter - voltage divider bias amplifier circuit

I'm designing a common emitter - voltage divider bias amplifier circuit like below: Requirements: $|A_v| = 5$ $Z_{in} \geqslant 10k\Omega$ $P_{consumption} \leqslant 0.2W$ $V_{CC} = 15V$ ...
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### Audio switch using NMOS (low level signal)

A common-emitter amplifier can include a bypass capacitor from the emitter to ground, resulting in considerable extra gain (1000uF in the picture). What happens if the bypass capacitor is switched &...
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### Transistor Driver - what is the purpose of Q2 on the included schematic?

I saw this schematic at the link below and I would like to know if there is any use in particular for Q2. Since the transistor Q2 is just, somehow, operating as a simple diode that is following the ...
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### How does resistance limit the gain in a common emitter amplifier? [closed]

I am having trouble understanding common emitter amplifiers. Can someone please explain how RE1 is limiting the gain of the amplifier in this circuit?
1 vote
256 views

### How to design BJT common collector amplifier?

I am working on a school project and I am struggling to design what is supposed to be an easy CC-amplifier. All other parts of the circuit are calculated and should work. The power amplifier is what's ...
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1 vote
97 views

### How can I eliminate cut-off [closed]

I have built a multistage bjt circuit. I got my gain to be around 40, but I cannot figure out how to eliminate the cut-off. The only values I can change are the resistor values (except the 50kOhm ...
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### What causes a negative voltage dip on the collector of common emitter NPN circuit at turn-off?

Circuit diagram: simulate this circuit – Schematic created using CircuitLab Observed waveforms: (Yellow: 3.3V square wave in, Magenta: Collector output) When the input square wave goes low and ...
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### Output characteristics of a BJT

While plotting the output characteristics of a CE configuration, the graph between VCE and IC, it shows that when VCE=0,IC=0 My doubt is whether VCE=0 means we are shorting collector and emitter or ...
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### Current mirrors with the voltage amplifiers

I am having a slight confusion with the current mirrors and their use with the common emitter amplifier. I have seen that the current mirrors can be used to bias the circuits and replace the need for ...
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### Why do we need a resistor across the transistor base-emitter junction?

I am still not very good at some of the basics. Why do we need the bottom resistor across VBE when the voltage drop is always 0.6 V (as VBE is acting as a forward bias in parallel to the resistor)? If ...
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### Single stage common emitter amplifier output voltage

I am having trouble getting the voltage Vout=1.25v and the gain should be Av=5 and I have the input voltage Vin = 0.25v. This is my schematic, what did I go wrong?
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### Stability factor and stiffness of voltage divider on a transitor

Does stability factor and stiffness of the bias network have a connection? this site mentioned something about stability factor so i was wondering if its thesame thumb rule about the current in ...
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### Highest DC current gain

I drew a circuit with a transistor (ktc3198) at heart for getting the highest DC gain the transistor can offer. I used its input and output characteristics. And based on that I made a little circuit. ...
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### Multistage common-emitter 2N4401 amplifier

I am trying to design a common-emitter multistage amplifier with gain 40 given $V_s(t)=0.25\sin(2\pi 1000t)$ and $V_o(t)=-10\sin(2\pi 1000t)$. Vcc is 24v and I want my q-point to be Vce=12v. I ...
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### Stage of Amplification In BJT [closed]

For a common emitter current amplifier, which current is more important: base current or collector to emitter current? And what's the connection amplification has with dc current gain?
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### How can I bias the two transistors (Q59, Q58) two main transistors in my common emitter pnp amplifier? [duplicate]

[ I tried in my design to make a common emitter stage amplifier using a pnp transistor and a npn transistor as a current source but I didn't know to bias either of them (well as for Q54 I think I've ...
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### Common Emitter Amplifier DC analysis

I have a standard common emitter amplifier biased using a voltage divider. I'm given that RE = 500 Ω, IC = 2.5mA, β=100, Vcc=15V and the coefficient of thermal stability K=10 (RE = K * Rth / (b+1) ...
1 vote
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### Troubleshooting class AB amp with only multimeter

I made a stereo amplifier on a PCB which is two of the following circuit. One channel amplifies the audio decently, but the other channel has NO sound regardless of how loud I make the input. My sound ...
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### Is it misleading to say a common emitter amplifier is “out-of-phase”?

I now understand that a common emitter amplifier produces an inverted amplification. I am asking this question because for a bit, I was hung up around the frequency with which I heard it explained as ...
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### My RF amplifier circuit works in LTSpice. Will it work in reality, too?

I am working now for a while with bias calculations. I have found a good turorial to calculate it by my own and I have seen that there are already calculators on internet, which made my life much ...
1 vote
104 views

### Biasing a BJT in a common emitter amplifier

I'm trying to design this common emitter amplifier to have a Q-point of $(V_C=2.5 V, I_C = 2.5 mA)$. According to my calculations (see below), if I were to use $R_2 = 100 k\Omega$, I should also ...
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1 vote
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### Common Emitter small signal model for high frequencies simplification

While trying to calculate the high frequency pole frequency corner of the common emitter amplifier I came across the following small signal model (found here in page 332) The small signal equivalent ...
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### High gain low current amp

I'm trying to design high gain, low collector current Common Emitter amplifier. As far as I know, this is well known CE amp for high gain. Is there anything I can do for low-current consumption? And ...
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### Signal saturating after transistor amplifier

I'm trying to amplify this noise coming from Q1 but it looks like it's saturating at the collector of Q2 (as you can see in the image). How can I resize the resistor values such that the signal does ...
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### What goes on inside the transistor that amplifies the signal?

I understand that, for example, in BJT NPN transistor in common emitter configuration used as amplifier, feeding the small signal at the base will produce the larger signal at the collector. But what ...
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### How to correctly bias an NPN transistor without allowing base voltage to be too high

simulate this circuit – Schematic created using CircuitLab I am trying to correctly bias a BC337 NPN whose collector is connected to a 9V source. I wish to use it as a switch in response to a ...
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### BJT amplifier design

I am trying to design a BJT amplifier with the given parameters and limitations. The circuit is shown below. Parameters: Vcc = 15 V RL = 20 kΩ beta = 180 Vbe(on)= 0.6 V Cµ = Cπ = 0 Limitations are: ...
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### Common emitter configuration opposite

What is the simplest circuit of common emitter configuration inverse that is switching to open on high base current and to close/shorted on no/low base current?
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### Active load role on this circuit and possible uses

simulate this circuit – Schematic created using CircuitLab I came with this circuit to know how an active load can improve it, I still can't finish to understand the role of active loads. The ...
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