Consider the following statements: FETs when compared to BJTs have1. h...
The correct statements comparing FETs and BJTs are as follows:
1. FETs have high input impedance. FETs are voltage-controlled devices, which means that they require very little input current to control the output current. This results in a high input impedance, making FETs suitable for applications where the input signal is weak or where low power consumption is desired.
2. FETs have current flow due to majority carriers. FETs are unipolar devices, which means that the current flow is primarily due to the movement of majority carriers (either electrons or holes). In an n-channel FET, the current flow is due to the movement of electrons, while in a p-channel FET, the current flow is due to the movement of holes.
3. BJTs have low input impedance. Unlike FETs, BJTs are current-controlled devices, which means that they require a significant input current to control the output current. This results in a low input impedance, making BJTs suitable for applications where high current gain is desired.
4. BJTs have current flow due to minority carriers. BJTs are bipolar devices, which means that the current flow is due to the movement of minority carriers (either electrons or holes). In an NPN transistor, the current flow is due to the movement of minority electrons, while in a PNP transistor, the current flow is due to the movement of minority holes.
To summarize, FETs have high input impedance and current flow due to majority carriers, while BJTs have low input impedance and current flow due to minority carriers. Therefore, the correct statements are 1 and 2, which correspond to option D: 1 and 2.
Consider the following statements: FETs when compared to BJTs have1. h...
Understanding FETs and BJTs
Before discussing the given statements, let's first understand the basic differences between FETs (Field-Effect Transistors) and BJTs (Bipolar Junction Transistors).
FETs:
- FETs are voltage-controlled devices.
- The majority carriers (electrons or holes) control the current flow in the device.
- FETs have three terminals: Gate (G), Source (S), and Drain (D).
- The gate-source voltage controls the current flow between the source and drain terminals.
- FETs have a high input impedance, meaning they require very little current to drive them.
BJTs:
- BJTs are current-controlled devices.
- The minority carriers (electrons or holes) control the current flow in the device.
- BJTs have three terminals: Base (B), Collector (C), and Emitter (E).
- The base current controls the current flow between the collector and emitter terminals.
- BJTs have a low input impedance, meaning they require a significant amount of current to drive them.
Analysis of the Given Statements
1. High input impedance: This statement is correct for FETs. FETs have a high input impedance due to the presence of a reverse-biased PN junction between the gate and the channel. This junction acts as a capacitor, allowing only a very small amount of current to flow into the gate terminal.
2. Current flow due to majority carriers: This statement is correct for FETs. The majority carriers (either electrons or holes) control the current flow in FETs. For example, in an n-channel FET, the current flow is controlled by the movement of electrons.
3. Low input impedance: This statement is incorrect for FETs. As mentioned earlier, FETs have a high input impedance due to the reverse-biased PN junction at the gate terminal.
4. Current flow due to minority carriers: This statement is incorrect for FETs. FETs operate based on the movement of majority carriers, not minority carriers. Minority carriers play a significant role in BJTs, where the base current controls the current flow between the collector and emitter terminals.
Conclusion
Based on the analysis above, the correct statements are:
- FETs have high input impedance (Statement 1).
- Current flow in FETs is due to majority carriers (Statement 2).
Therefore, the correct option is D) 1 and 2.
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