A common base is one of three basic bipolar junction transistor (BJT) amplifier topologies. It has a low input impedance, produces a high voltage gain, but its current gain is less than 1. Its high-frequency characteristics are better than of the other two BJT amplifier topologies.
Questions tagged [common-base]
41 questions
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Is a special BJT transistor to use in Common Base configuration?
Revisting multistage amplifier consists of Common Source-Common Base-Emitter Follower in cascading, I found the attached page of MPS-H85 PNP transistor that is proposed special for common base application.
Is any unique characteristic for CB…
GR Tech
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Discrete component FM radio receiver circuit - explanation needed
I have built an FM radio receiver from a kit. I'm very happy with the results! It is the Sinclair Micro FM.
My goal is to learn about discrete electronics (NO IC's.)
The radio works great, but I am having trouble understanding the very first…
dhrovner
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Does changing the collector resistance of a common base amplifier have any effect on the current?
I have come across this equation for understanding the voltage gain of a common base amplifier:
$$
A_v = \frac{I_c R_c }{I_e R_e}
$$
Because base current is small, Ic and Ie are roughly equal. Therefore, the gain is essentially just a ratio of the…
shafe
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Common base amplifier's input impedance
simulate this circuit – Schematic created using CircuitLab
In a BJT common base amplifier configuration the input impedance is ~\$r'\$ (emitter resistance), right?
If I understand correctly, there is no current flowing from emitter to base (as…
TheUnknown
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Question about the BJT emitter resistance
I'm trying to teach myself a little bit about BJTs, particularly through the Art of Electronics. I came across something I've been trying for days to wrap my head around. (page 92, third edition)
I cannot for the life of me figure out why the…
Vortex123
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Common Base amp gain problem
simulate this circuit – Schematic created using CircuitLab
Here's a little schematic I built for my 27MHz colpitts oscillator, which outputs approximately 120mVpp. Since the common base is less dependent on frequency, is less prone to distortion…
Anthropomorphous Dodecahedron
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Why does the emitter current increase with an increase in collector to base voltage in the common base configuration of a BJT?
It is said that because of the Early effect that with an increase in collector to base voltage there is decrease in base width due to which \$\alpha\$ (the current gain) increases due to lesser recombination of holes and electron, so with increase…
Kartik Watwani
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Why is KCL giving me the wrong solution?
I'm trying to derive the gain of the following common base amplifier circuit:
To do this, I drew the equivalent T-model circuit: .
The problem I have is that I get two different transfer functions for \$\frac{v_{out}}{v_{in}}\$ depending on which…
user3533714
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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. These confusions have risen perhaps due to unclear…
MSKB
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Common Base Amplifier Confusion
In the CB configuration, a signal is applied to the emitter to create an in-phase amplification at the collector. I am confused, however, on how exactly this happens. In the picture below, if the input signal raises the emitter voltage on the…
jm567
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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-emitter junction in the common base configuration…
MSKB
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Why does a common base amplifier give a non inverting output?
I am unable to understand why a common base amplifier gives a non-inverting output.
My reasoning so far:
Let's take a look at the common collector (emitter follower) amplifier. Here \$V_e = V_b -0.7\$. So on differentiating we get \$ d{V_e} =…
shahrOZe
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What happens when input current in common base amplifier circuit is increased?
Looking at the equations of the common base amplifier circuit shown below:
The input current should be given by the equation: $$I_e = (V_{in} - 0.7)/R_e$$
Then, the output current should be: $$I_c = \frac{\beta}{\beta + 1} I_e$$
Taking KVL on the…
user3407319
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When two transistors connected which one is on and which one is in cutoff from given circuit condition?
here in this question's solution, given that upper BJT is on while lower one is in cutoff region for Vbb = 2.7 V and viceversa for Vbb = -2.7 V and both will be in cutoff for 0 V.
While in other problem Q1 is on and Q2 is in cutoff.
So my question…
user146551
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All possible BJT circuits relating to polarity
The BJT can operate in 4 different modes/zones since there are two voltages on it:
Active mode
Inverse/Reverse active mode
Saturation mode
Cut-off mode
Because Emitter and Collector junctions can be represented as diodes (with amplification)…
Keno
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