Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [common-source]

A common source is one of the three basic FET topologies. It is distinguished by the fact that the input is at the FET's gate and the output is at the drain, leaving the FET's source as the "common" terminal. It typically exhibits high voltage gain but low bandwidth. Consider also using the "fet" or "mosfet" tag, as applicable.

A common source is one of the three basic FET topologies. It is distinguished by the fact that the input is at the FET's gate and the output is at the drain, leaving the FET's source as the "common" terminal. It typically exhibits high voltage gain but low bandwidth. The BJT equivalent topology is the common emitter.

Consider also using or , as applicable.

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Help biasing this JFET buffer

I'm trying to make a simple JFET buffer but I am struggling to find clear instructions on how to calculate the bias resistors. I've built a circuit which nearly works, but I'm getting well below unity gain. The resistor values are taken from a…
jcansell
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Why is the saturation region linear in the Vds v/s Vgs graph?

Looking at the problem mathematically, we see the equations $$I_\text{ds}=k_n'(V_\text{gs}-V_t)^2$$ $$V_\text{ds}=V_\text{dd}-I_\text{ds} \times R_o$$ Following this, it would be predictable that \$V_\text{ds}\$ vs. \$V_\text{gs}\$ would have a…
Janhvi
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Calculation of power dissipation of a MOSFET circuit

As a part of an assignment to design a common source amplifier, I came up with this circuit: simulate this circuit – Schematic created using CircuitLab The transistor is a 180nm technology with aspect ratio 2 and early voltage 0.9V for it's…
KaBe2003
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Why should we set input source equal zero for calculating output resistance of common source amplifier?

This lecture (page 10) gave derivation of common source output resistance. What I don't quite get here is why we should set the input source equal 0 for calculating output resistance. Why?
emnha
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Obtaining the expression of the noise figure for this common source

I'm trying to obtain the expression of the noise figure defined for this circuit : The transistor is in saturation, and strong inversion. The flicker noise can be ignored. Here is my attempt: For the output noise of \$R_s\$, I just multiplied the…
Scipio
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Input capacitance of common source amplifier

I am trying to find the input capacitance for the common source amplifier stage below: - I have tried to find \$C_{in} \$ by simulation. I apply a linearly increasing voltage source \$v_{in}(t) = 1 \text{V} \cdot t \$. By doing this, I should be…
Carl
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Common Source MOSFET Amplifier Biasing

While reviewing simple transistor amplifier biasing techniques I came across this paragraph in Microelectronic Circuits by Sedra & Smith. Here too we show the \$i_D–v_{GS}\$ characteristics for two devices that represent the extremes of a batch of…
Heymor
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CS amplifier feedback stability

I playing with JFET Common Source amplifier with feedback loop. I am simulating the design showed here. https://www.ti.com/lit/an/slpa018/slpa018.pdf?ts=1669662908797&ref_url=https%253A%252F%252Fwww.google.com%252F I followed the steps for feedback…
Peter Hrčka
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How to bias a common-source amplifier with a current-source load in moderate inversion?

I am using the gmid method to design a common-source amplifier. The gmid method forgoes the use of the square-law equations for lookup-tables/charts to provide accurate results when designing circuits. Consider the common-source amplifier shown…
Leonhard Euler
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Biasing for complementary common-source stage amplifier

Why does no current flow through \$R_F\$ in the absence of signals in Fig 5.47(b)? This can only happen if \$V_x = V_\text{out}\$. How is that guaranteed??
alayoiskgfbfqhxjiw
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Bipolar junction transistor circuit added after common source amplifier

I am studying for a class at university and our teacher gave us this circuit diagram and asked us to calculate the amplification, the DC version of the circuit and the small signal model for it. I have seen the common source amplifier before but I…
assassinduke
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How to design a common source amplifier with active loading

I am quite new to amplifier. I want to design a common source amplifier. And here is my design in spice: Since the supply voltage is 6V. So i want my amplifier's operating point at 3V. So before i add the active loading.It is quite easy to do…
Mirage
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Need help understanding current source loading common source amplifier

For the circuit in the diagram, I observe that Vgs is around 3V and so is Vds on the breadboard. I do not understand if it is necessary to keep the drain at 1/2 of V1 as it is done when using a drain resistor? I am observing that the output is…
cd2021
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Understanding the role of the FET in this opamp + Zener diode voltage regulator

I'm trying to repair my old audio CD player, and I've found a fault in or around this voltage regulator circuit (it's sourcing VCC for the DAC chip): I understand how the Zener + opamp work to produce Zener-limited voltage with higher current load…
Violet Giraffe
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Common Source vs. Common Drain for N-Channel Switches

Most discrete load switches I have seen (Using N-Channel FETs) have been in the common-source configuration. What, if any, are the operational differences between this and the common-drain configuration? I understand that a gate driver with a charge…
Tim Vermilyea
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