JFET Characteristics: Identifying the Incorrect Statement
This question asks us to identify the statement about Junction Field-Effect Transistors (JFETs) that is not true. Let's analyze each option:
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Statement 1: It has a high input impedance.
This statement is correct. JFETs have a very high input impedance because the gate terminal is isolated from the channel by a reverse-biased PN junction. This reverse-biased junction allows very little current to flow, resulting in high impedance, typically in the range of $10^9$ to $10^{12}$ ohms. This is a significant advantage over Bipolar Junction Transistors (BJTs).
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Statement 2: It generates large noise as compared to BJT.
This statement is incorrect. JFETs are generally known for producing less noise than BJTs, especially at lower frequencies. The primary noise sources in a JFET are thermal (or Johnson) noise in the channel resistance and generation-recombination noise. BJTs, on the other hand, suffer from shot noise and recombination noise in both the base and collector regions, which often results in higher noise levels compared to JFETs under similar operating conditions.
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Statement 3: It is a three-terminal voltage controlled device.
This statement is correct. A JFET has three terminals: Gate (G), Drain (D), and Source (S). The current flowing through the channel between the drain and source ($I_D$) is controlled by the voltage applied between the gate and source terminals ($V_{GS}$). It is therefore a voltage-controlled device.
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Statement 4: It is also called unipolar transistor.
This statement is correct. JFETs are called unipolar devices because the current conduction is solely due to one type of charge carrier – either electrons (in N-channel JFETs) or holes (in P-channel JFETs). This contrasts with BJTs, which are bipolar devices as both electrons and holes participate in current conduction.
Conclusion on JFET Properties
Based on the analysis of each statement, the statement that is factually incorrect regarding JFETs is that they generate large noise compared to BJTs. JFETs typically exhibit lower noise levels.
Important Questions from Types of FET
A JFET is also called ________ device.
In JFET, the Pinch‐off Voltage can be defined as:
In JFET, the current density in the x-direction is:
A. σ(x)E x
B. qN DμE x
C. \(\rm \frac{q}{2 \in_s}N_D\mu\)
D. \(\rm \frac{N_D\mu}{2 \in_s}\)
Choose the correct answer from the options given below:
The pull up to pull down ratio for an n mos inverter driven by another n mos inverter can be evaluated from:
(A) Vi nv = V t − \(\rm\frac{V_{t d}}{\sqrt{Zpu/Zpd}}\)
(B) V inv = \(\rm\frac{−V_{t d}}{\sqrt{Zpu/Zpd}}\)
(C) \(\rm\frac{W_{pd}}{L_{pd}}\) (V inv − V t) 2= \(\rm\frac{W_{p u}}{L_{p u}}\) (−V td )2
(D) \(\rm\frac{W_{p d}}{L_{p d}}\) (V inv − V t ) = \(\rm\frac{W_{p u}}{L_{pu}}\) (−V td )2
Choose the correct answer from the options given below:
The layers of Nos involves a subset of layers. For NMOS we require:
(A) Contact, (Black or Brown)
(B) Polysilicon (Green)
(C) Metal (Blue)
(D) Implant (Yellow)
Choose the correct answer from the options given below:
