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Some questions about common drain amplfier

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sherline123

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Hi,
I have some questions about common drain amplfier. Common drain is known as source follower/voltage buffer. But in large signal, I thought the highest output it could only be Vin - vth? Why it is called as voltage buffer or source follower since it should won't reach the level of Vin
 

if Vin changes with dV the source will follow the input and it will change with dV too. But Vin never equals with the source voltage.
it is called buffer from else reason, the output resistance is lower than other basic circuits, but the input resistance is not lower.
 

A CS amplifier is a voltage follower but a current buffer, as it can deliver more current than a high impedance source could.
The output voltage "follows" the input with a voltage offset due to the FET Vgs(threshold) voltage.
 

Hi,
After proper biasing, the input signal is applied and you take the output from the Drain terminal (in nmos). You can see that the phase is same as that of input ,thats why its voltage follower. and the input is not that large that it can take your circuit to the edge of saturation if you have wisely choosen your operating point.
 

Akshaay said:
Hi,
After proper biasing, the input signal is applied and you take the output from the Drain terminal (in nmos). You can see that the phase is same as that of input ,thats why its voltage follower. and the input is not that large that it can take your circuit to the edge of saturation if you have wisely choosen your operating point.
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Typing error? Must be "source terminal".
 

I am sorry but i thought common gate is the one called current buffer?
 

sherline123 said:
I am sorry but i thought common gate is the one called current buffer?
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No.
The common drain (aka source follower) configuration is a current buffer.

The common gate configuration (grounded gate) has voltage gain with a low-impedance input.
 

crutschow said:
No.
The common drain (aka source follower) configuration is a current buffer.

The common gate configuration (grounded gate) has voltage gain with a low-impedance input.
Click to expand...

In electronics, a common-gate amplifier is one of three basic single-stage field-effect transistor (FET) amplifier topologies, typically used as a current buffer or voltage amplifier **source from wikipedia**
In electronics, a common-drain amplifier, also known as a source follower, is one of three basic single-stage field effect transistor (FET) amplifier topologies, typically used as a voltage buffer **source from wikipedia**
 

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