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Don't understand MOSFET as amplifier


How is possible that with same Ibase there is more than one Vce?My amplifier produced a negative gain when it should be positive. Why?Designing a BJT Amplifier given some constraintsAoE3: Grounded Emitter Amplifier DistortionGain and output impedance of an amplifierHow does the voltage difference develop when MOSFET is biased with Current Source?Common source amplifier using mosfet: Why is my Id dependent on my Rd?Difficulties in biasing MOSFET push-pull amplifierHow to identify which transistor is in active region and which one is in saturation?About the output resistance of a voltage amplifier






.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;








1












$begingroup$


When a MOSFET is working in its saturation region, it might be used as an amplifier. But, as far as I understand, the more you increase vGS (voltage between the MOSFET's gate and ground) the less output voltage you get, which is the opposite of amplifying. Let me explain:



Having this (supposed) amplifier:



enter image description here



when it is in saturation region, it behaves as a VCCS, which, apparently, leads to an amplifiers' behaviour:



enter image description here



In the above picture, vO will be VS - eL, if eL is the voltage drop in RL. Following the iD equation, the more vIN incrases, the more voltage drop you will have in RL, right? That means that the more vIN increases, the more vO decreases. That isn't amplifying, but the opposite.



What am I missing?










share|improve this question









$endgroup$









  • 3




    $begingroup$
    This is an inverting amplifier, so the AC gain has a negative sign.
    $endgroup$
    – glen_geek
    8 hours ago











  • $begingroup$
    If |ΔVo/ΔVin| >1 then it is amplifying.
    $endgroup$
    – Phil G
    8 hours ago










  • $begingroup$
    electronics.stackexchange.com/questions/355899/…
    $endgroup$
    – G36
    8 hours ago

















1












$begingroup$


When a MOSFET is working in its saturation region, it might be used as an amplifier. But, as far as I understand, the more you increase vGS (voltage between the MOSFET's gate and ground) the less output voltage you get, which is the opposite of amplifying. Let me explain:



Having this (supposed) amplifier:



enter image description here



when it is in saturation region, it behaves as a VCCS, which, apparently, leads to an amplifiers' behaviour:



enter image description here



In the above picture, vO will be VS - eL, if eL is the voltage drop in RL. Following the iD equation, the more vIN incrases, the more voltage drop you will have in RL, right? That means that the more vIN increases, the more vO decreases. That isn't amplifying, but the opposite.



What am I missing?










share|improve this question









$endgroup$









  • 3




    $begingroup$
    This is an inverting amplifier, so the AC gain has a negative sign.
    $endgroup$
    – glen_geek
    8 hours ago











  • $begingroup$
    If |ΔVo/ΔVin| >1 then it is amplifying.
    $endgroup$
    – Phil G
    8 hours ago










  • $begingroup$
    electronics.stackexchange.com/questions/355899/…
    $endgroup$
    – G36
    8 hours ago













1












1








1





$begingroup$


When a MOSFET is working in its saturation region, it might be used as an amplifier. But, as far as I understand, the more you increase vGS (voltage between the MOSFET's gate and ground) the less output voltage you get, which is the opposite of amplifying. Let me explain:



Having this (supposed) amplifier:



enter image description here



when it is in saturation region, it behaves as a VCCS, which, apparently, leads to an amplifiers' behaviour:



enter image description here



In the above picture, vO will be VS - eL, if eL is the voltage drop in RL. Following the iD equation, the more vIN incrases, the more voltage drop you will have in RL, right? That means that the more vIN increases, the more vO decreases. That isn't amplifying, but the opposite.



What am I missing?










share|improve this question









$endgroup$




When a MOSFET is working in its saturation region, it might be used as an amplifier. But, as far as I understand, the more you increase vGS (voltage between the MOSFET's gate and ground) the less output voltage you get, which is the opposite of amplifying. Let me explain:



Having this (supposed) amplifier:



enter image description here



when it is in saturation region, it behaves as a VCCS, which, apparently, leads to an amplifiers' behaviour:



enter image description here



In the above picture, vO will be VS - eL, if eL is the voltage drop in RL. Following the iD equation, the more vIN incrases, the more voltage drop you will have in RL, right? That means that the more vIN increases, the more vO decreases. That isn't amplifying, but the opposite.



What am I missing?







mosfet amplifier






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 8 hours ago









MartelMartel

155 bronze badges




155 bronze badges










  • 3




    $begingroup$
    This is an inverting amplifier, so the AC gain has a negative sign.
    $endgroup$
    – glen_geek
    8 hours ago











  • $begingroup$
    If |ΔVo/ΔVin| >1 then it is amplifying.
    $endgroup$
    – Phil G
    8 hours ago










  • $begingroup$
    electronics.stackexchange.com/questions/355899/…
    $endgroup$
    – G36
    8 hours ago












  • 3




    $begingroup$
    This is an inverting amplifier, so the AC gain has a negative sign.
    $endgroup$
    – glen_geek
    8 hours ago











  • $begingroup$
    If |ΔVo/ΔVin| >1 then it is amplifying.
    $endgroup$
    – Phil G
    8 hours ago










  • $begingroup$
    electronics.stackexchange.com/questions/355899/…
    $endgroup$
    – G36
    8 hours ago







3




3




$begingroup$
This is an inverting amplifier, so the AC gain has a negative sign.
$endgroup$
– glen_geek
8 hours ago





$begingroup$
This is an inverting amplifier, so the AC gain has a negative sign.
$endgroup$
– glen_geek
8 hours ago













$begingroup$
If |ΔVo/ΔVin| >1 then it is amplifying.
$endgroup$
– Phil G
8 hours ago




$begingroup$
If |ΔVo/ΔVin| >1 then it is amplifying.
$endgroup$
– Phil G
8 hours ago












$begingroup$
electronics.stackexchange.com/questions/355899/…
$endgroup$
– G36
8 hours ago




$begingroup$
electronics.stackexchange.com/questions/355899/…
$endgroup$
– G36
8 hours ago










1 Answer
1






active

oldest

votes


















6












$begingroup$

It is an amplifier because you put a wiggly signal in, and you get a bigger wiggly signal out. The fact that the output wiggles down when the input wiggles up is a trivial detail, that -- if it's a problem at all -- can be solved in any number of ways (not least of which is following one stage by another, because two negative gains, when multiplied, result in a positive gain).






share|improve this answer









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    1 Answer
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    1 Answer
    1






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    oldest

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    active

    oldest

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    active

    oldest

    votes









    6












    $begingroup$

    It is an amplifier because you put a wiggly signal in, and you get a bigger wiggly signal out. The fact that the output wiggles down when the input wiggles up is a trivial detail, that -- if it's a problem at all -- can be solved in any number of ways (not least of which is following one stage by another, because two negative gains, when multiplied, result in a positive gain).






    share|improve this answer









    $endgroup$



















      6












      $begingroup$

      It is an amplifier because you put a wiggly signal in, and you get a bigger wiggly signal out. The fact that the output wiggles down when the input wiggles up is a trivial detail, that -- if it's a problem at all -- can be solved in any number of ways (not least of which is following one stage by another, because two negative gains, when multiplied, result in a positive gain).






      share|improve this answer









      $endgroup$

















        6












        6








        6





        $begingroup$

        It is an amplifier because you put a wiggly signal in, and you get a bigger wiggly signal out. The fact that the output wiggles down when the input wiggles up is a trivial detail, that -- if it's a problem at all -- can be solved in any number of ways (not least of which is following one stage by another, because two negative gains, when multiplied, result in a positive gain).






        share|improve this answer









        $endgroup$



        It is an amplifier because you put a wiggly signal in, and you get a bigger wiggly signal out. The fact that the output wiggles down when the input wiggles up is a trivial detail, that -- if it's a problem at all -- can be solved in any number of ways (not least of which is following one stage by another, because two negative gains, when multiplied, result in a positive gain).







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 8 hours ago









        TimWescottTimWescott

        12.3k1 gold badge9 silver badges24 bronze badges




        12.3k1 gold badge9 silver badges24 bronze badges






























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