Name: mosfet gain and biasing
Uploaded: 2024-07-08T13:20:42.000Z
Duration: 1 min 17 s
Channel: JoVE

Il MOSFET funziona come una sorgente di corrente controllata in tensione nella sua regione attiva, dove la tensione gate-to-source regola la corrente di drain.
Questo amplificatore MOSFET a transconduttanza può essere convertito in un amplificatore di tensione dirigendo la corrente di uscita attraverso un resistore.
La tensione di uscita si ottiene sottraendo la caduta di tensione attraverso la resistenza di carico dalla tensione di alimentazione. Ciò si traduce in una versione invertita della tensione di uscita, spostata dalla tensione di alimentazione.
Il grafico delle caratteristiche di trasferimento di tensione dell'amplificatore illustra la relazione tra il drain di uscita e la tensione di gate di ingresso.
Evidenzia la regione attiva dell'amplificatore, con una pendenza ripida per il massimo guadagno ma una tensione di drain non lineare.
L'applicazione di una polarizzazione di tensione CC gate-to-source nel punto di riposo all'interno della regione attiva si traduce tipicamente in un'amplificazione quasi lineare dal MOSFET.
Quando un piccolo segnale variabile nel tempo viene applicato all'amplificatore, si sovrappone alla tensione di polarizzazione CC attorno al punto Q.
Il MOSFET opera all'interno di un segmento corto e quasi lineare della curva caratteristica, con conseguente tensione di drain di uscita amplificata.

i transistor

Il MOSFET, quando opera nella sua regione attiva, funziona come una sorgente di corrente controllata in tensione. In questa regione, la tensione gate-source controlla la corrente di drain. Questo principio è alla base del funzionamento dell'amplificatore MOSFET a transconduttanza. La corrente di uscita viene diretta attraverso un resistore di carico per convertire questo amplificatore in un amplificatore di tensione. La tensione di uscita viene quindi ottenuta sottraendo la caduta di tensione attraverso la resistenza di carico, dalla tensione di alimentazione. Questo processo si traduce in una tensione di uscita invertita che viene spostata dalla tensione di alimentazione.


Il grafico delle caratteristiche di trasferimento di tensione dell'amplificatore, illustra la relazione tra la tensione di drain di uscita e la tensione di gate di ingresso. Questo grafico è fondamentale per comprendere il comportamento dell'amplificatore. Evidenzia la regione attiva dell'amplificatore, dove la pendenza della curva è ripida, indicando il guadagno massimo. Tuttavia, questa regione è anche non lineare in termini di tensione di drain.


Una polarizzazione di tensione CC, viene applicata alla giunzione gate-source per ottenere un'amplificazione quasi lineare, posizionando il MOSFET in un punto quiescente (punto Q) all'interno della regione attiva. Questa polarizzazione garantisce che il MOSFET operi in una regione in cui il suo comportamento è approssimativamente lineare. Quando un piccolo segnale variabile nel tempo viene sovrapposto a questa tensione di polarizzazione CC, fa sì che il MOSFET funzioni attorno al punto Q. Il MOSFET, di conseguenza, funziona all'interno di un breve segmento quasi lineare della sua curva caratteristica, risultando in una tensione di drain di uscita amplificata.


Nelle applicazioni pratiche, questa configurazione consente all'amplificatore MOSFET di amplificare efficacemente piccoli segnali CA. L'amplificazione avviene perché il piccolo segnale di ingresso modula la tensione di gate attorno al punto Q, provocando variazioni proporzionali nella corrente di drain. Queste variazioni si traducono in una tensione di uscita maggiore attraverso il resistore di carico, ottenendo di conseguenza un'amplificazione.

I Transistor

Il MOSFET funziona come una sorgente di corrente controllata in tensione nella sua regione attiva, dove la tensione gate-to-source regola la corrente di drain.
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MOSFET Amplifiers

mosfet gain and biasing

MOSFET gain and biasing shape how a MOSFET amplifier works. When a MOSFET operates in its active region, it acts like a voltage-controlled current source. The gate-to-source voltage sets the drain current, and that behavior supports transconductance amplification.

The output current then flows through a load resistor. That load resistor turns the circuit into a voltage amplifier. The output voltage is found by subtracting the voltage drop across the load resistor from the supply voltage, so the result is inverted and shifted by the supply voltage.

A voltage-transfer characteristic plot shows how the output drain voltage changes with the input gate voltage. This curve helps explain the amplifier’s behavior. The active region has a steep slope and gives maximum gain, but it is also nonlinear in drain voltage.

To make the amplification nearly linear, a DC bias voltage is applied to the gate-to-source junction. This sets the MOSFET at a quiescent point, or Q-point, inside the active region. A small time-varying signal can then ride on top of the DC bias and keep the MOSFET operating around that point.

Around the Q-point, the MOSFET uses only a short, nearly linear part of its characteristic curve. That lets it amplify small AC signals effectively. Small changes in gate voltage cause proportional changes in drain current, and the load resistor turns those current changes into a larger output drain voltage.

MOSFET Gain and Biasing

bipolar junction transistor

BJT Structure and Carrier Flow

Bipolar junction transistors are important parts of electronic circuits. They help make amplifiers, memories, and microprocessors work. A BJT can be built as either NPN or PNP, depending on its doping pattern, which means the type of impurities added to the material. A BJT has three layers: the emitter, base, and collector. It also has two p-n junctions, so the device has a sandwich-like structure. The emitter is heavily doped so it can inject charge carriers into the base. The base is very...

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PNP bipolar junction transistors control current flow by moving charge carriers between the emitter, base, and collector. In a common-base setup, the transistor can amplify or switch electronic signals when it operates in active mode. In a PNP transistor, the emitter is heavily doped with holes, which are positive charge carriers. The base is lightly doped with electrons, which are negative carriers. A forward bias across the emitter-base junction lowers the potential barrier and lets holes...

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BJT Current-Voltage Curves in Common Emitter

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BJT Biasing: Active to Inverted Mode

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BJT Amplifier Response at Low and High Freq

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BJT Frequency Limits and Gain Drop

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BJT Amplifier Gain and Input Resistance

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JFET Output Regions and Current Control

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MOSFET Current Control in Electronics

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MOSFET Structure and Operating Regions

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Depletion MOSFET Channel Control

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mosfet amplifiers

MOSFET gain and biasing shape how a MOSFET amplifier works. When a MOSFET operates in its active region, it acts like a voltage-controlled current source. The gate-to-source voltage sets the drain current, and that behavior supports transconductance amplification. The output current then flows through a load resistor. That load resistor turns the circuit into a voltage amplifier. The output voltage is found by subtracting the voltage drop across the load resistor from the supply voltage, so...

small-signal analysis of mosfet amplifiers

small-signal-analysis-of-mosfet-amplifiers

MOSFET Amplifier Gain and Signal Distortion

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key terms and concepts

Learn how MOSFET biasing sets a Q-point, how the load resistor creates voltage gain, and why the output signal is inverted in the active region.

MOSFET Gain and Biasing | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

MOSFET Gain and Biasing

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