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    Some questions about common drain amplfier

    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

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    Re: Some questions about common drain amplfier

    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.
    "Try SCE to AUX." /John Aaron/



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    Re: Some questions about common drain amplfier

    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.
    Zapper
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    Re: Some questions about common drain amplfier

    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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    Re: Some questions about common drain amplfier

    In post #3 it should be a CD amplifier, not CS.
    Zapper
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    Re: Some questions about common drain amplfier

    Quote Originally Posted by Akshaay View Post
    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.
    Typing error? Must be "source terminal".



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    Re: Some questions about common drain amplfier

    Quote Originally Posted by LvW View Post
    Typing error? Must be "source terminal".
    Oh, sorry. Thats source terminal. Thanks for correcting



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    Re: Some questions about common drain amplfier

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



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    Re: Some questions about common drain amplfier

    Quote Originally Posted by sherline123 View Post
    I am sorry but i thought common gate is the one called current buffer?
    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.
    Zapper
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    Re: Some questions about common drain amplfier

    Quote Originally Posted by crutschow View Post
    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.
    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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