Field-Effect Transistor (FET) is a three-terminal devices such as BJT transistors. The main difference of the two transistors is that the BJT is a device which is controlled by flow, while the FET is a voltage-controlled devices.
A BJT is a bipolar transistor in the sense that there are two kinds of charge carrier in dalamnya.Dalam trnsistor npn main operator in the hole and in the pnp JFET elektron.Dalam pembawa.Dalam there is only one type of carrier n-channel case elctron and p-channel hole. So JFET is a unipolar in the sense.
BJT is a current controlled device as the input currents strengthened subject to operasi.Misalnya mode in CE mode input current and output currents emmiter base current flows (β 1) times diperkuat.Drop current throughout the load voltage is the voltage signal JFET keluaran.Tapi is the device conductance is controlled tegangan.The chalnnel determned by the applied voltage at the gate terminal and depending on the channel current flows.
MOSFET is one type of voltage-controlled devices such as JFETs where there are metal oxide between the gate and saluran.Tergantung on applied voltage at a terminal gate voltahe is 'caused' by electrostatic induction in the channel terisolasi.Oleh because it behaves as a channel because voltage capacitors where several charges this terinduksi.Tuduhan shrink or extend the width of channel MOSFET efektif.Sebagai examples effectively increase the channel width increases and the depletion MOSFET is berkurang.Tergantung on this channel for the current source increases or decreases.
Control voltage, current and charge
Collector-emitter current can be viewed as the base-emitter current control (current control) or the base-emitter voltage (control voltage). This view is related to the current-voltage relationship from meeting the base-emitter junction, which is only an exponential voltage-current curve of the diode ordinary physics pn.Penjelasan meeting for the collector current is the sum of minority carrier charge on the base region. Detailed model of the transistors work, Gummel-Poon model, calculating the distribution of these charges explicitly to explain the behavior of transistors with more precision. This view of control-easily handle the load transistor-images, where minority carriers in the base region are generated by photon absorption, and handle the dynamic extinction or recovery time, which depends on the charge recombination in the base region. However, because the base charge is a sign that can be measured on the channel, view current and voltage control is usually used in circuit design and analysis.
In analog circuit design, view current control is often used because it is almost linear. Collector current approximately βF times the base current. Several basic circuit can be designed to assume that the emitter-base voltage approximately constant, and the collector current is beta times the base current. However, for designing circuit BJT with accurate and reliable, we need a model of control-voltage (for example Ebers-Moll model).
The voltage-control model requires an exponential function that must be taken into account, but if this dilinierkan, the transistor can be modeled as a transconductance, as in the Ebers-Moll model, circuit design for such a problem of linear differential amplifier, so the view-voltage control is often preferred. For translinier circuit, where the curve eksponensiak IV is the key of the operation, the transistor is modeled as a controlled voltage to the transconductance is proportional to the collector current.