Questions tagged [common-base]
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.
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Common base bias divider resistances
I have been trying to grok the common base amplifier, and put together a few examples, but there is something that I do not get at all. I have the setup below. Things are working more or less as ...
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2answers
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finding output resistance of CB amplifier with ro
I have this CB amplifier circuit below
This is the small signal equivalent circuit arranged to find the output resistance R_out with the r_o included
Here is my analysis below to find the output ...
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Purpose of PNP transistor in ultrasonic driver circuit
This question is related to my other question
What is the purpose of Q2, R2, C1 and C6 in the circuit in the original question?
When I remove these components from the simulation nothing appears to ...
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2answers
132 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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2answers
573 views
BJT common-base output resistance derivation
In Sedra/Smith the following image may be founded that is used for output resistance equation derivation of common-base BJT amplifier. The question is why the gm*v and v/re currents are directed up? ...
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1answer
777 views
Common base amplifier output impedance
In Sedra Smith I can found that: Rout = ro + (1 + gm * ro) * Re_s, Re_s = Re || r_pi. Can I see in my circuit using simulation tools (like current probe, voltage meter) that previous equation ...
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2answers
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Confusion with power amplification concept in common base topology
A text is telling that a transistor can amplify power and gives common base amplifier as an example.
Here is what it mentions:
But what is the use of the transistor here?
Below I draw the same ...
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4answers
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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 ...
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1answer
453 views
Collector current decreases with the increase of base current in saturation mode of bjt
I'm new to BJT and i'm trying to understand the characteristics of bjt in different modes of it. In my book they explained that in saturation mode of bjt the collector current decreases even if i ...
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3answers
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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 ...
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1answer
220 views
Transistor noise figure in common base / common gate configuration
My question regards BJT and JFET devices.
Noise figures for transistors are usually given along with specific signal source resistances and collector / drain currents.
How can one apply these ...
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1answer
197 views
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 ...
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2answers
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Strange colpitt's oscillator(s)
I'm currently building a theremin from the circuits form here:LINK
This uses Colpitts oscillators. However, when I've tried calculating the frequency, for example of the fixed-pitch oscillator (below),...
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1answer
612 views
Why Emitter current increases with increase in collector to base voltage in common base configuration of a BJT?
It is said from early effect that with 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 ...
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2answers
474 views
Common base circuit with zero supply voltage
Consider a bipolar junction transistor (either PNP or NPN). Which output would produce this circuit for various input (\$= V_{\mathrm{BE}}\$) voltages?
It is common base, but without a voltage supply ...
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3answers
292 views
Transistor Common Base configuration
It is said that for a common base configuration the base is grounded, i.e. at zero potential.
But at forward biased for a npn transistor, the battery used to forward bias emitter–base junction is ...
