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Questions and Answers
What is the main characteristic of the active region in a common-base configuration?
Which current is defined as the collector-to-base current with the emitter leg open?
What happens to the collector current ($I_C$) when the current $I_E$ is equal to zero?
What does the symbol with an arrow represent in the context of transistor operation?
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In which region is the current $I_{CO}$ negligible due to improved construction techniques in modern transistors?
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Why does the cutoff region appear horizontal in the $I_C$ versus $V_{CB}$ graph?
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What is represented on the output characteristic curve for a common-base amplifier?
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Which two sets of characteristics are necessary to fully describe a three-terminal device like a common-base amplifier?
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Study Notes
Common-Base Configuration
- The common-base configuration in transistors has the base terminal connected to both the input and output.
- Current flow in the text is referred to as conventional (hole) flow, where arrows indicate the direction of current flow.
- Emitter current (IEI_EIE) is defined by the arrow in the graphic symbol and represents the direction of conventional current through the device.
- The relationship between currents is: IE=IC+IBI_E = I_C + I_BIE=IC+IB.
- Biasing voltage sources are oriented in a specific direction for each branch.
Common-Base Transistor Characteristics
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Input Characteristics: This set relates input current (IEI_EIE) to input voltage (VBEV_{BE}VBE) for various levels of output voltage (VCBV_{CB}VCB).
- The relationship between input current (IEI_EIE) and input voltage (VBEV_{BE}VBE) is depicted in the input characteristics curve.
- The curve changes based on different output voltage (VCBV_{CB}VCB) levels.
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Output Characteristics: This set relates output current (ICI_CIC) to output voltage (VCBV_{CB}VCB) for various levels of input current (IEI_EIE).
- The output characteristics curve shows the relationship between output current (ICI_CIC) and output voltage (VCBV_{CB}VCB) for various input current (IEI_EIE) levels.
- The curve has three distinct regions: active, cutoff, and saturation.
Transistor Regions of Operation
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Active Region: The base-emitter junction is forward-biased, while the collector-base junction is reverse-biased. This region is characterized by a linear relationship between input and output current.
- When IEI_EIE is zero, ICI_CIC is solely due to reverse saturation current (ICOI_{CO}ICO).
- Cutoff Region: In this region, both junctions are reverse-biased, leading to minimal current flow, essentially zero collector current (ICI_CIC).
- Saturation Region: The collector-base junction is forward-biased leading to a higher current flow compared to the active region and very low collector-emitter voltage.
Reverse Saturation Current (ICBOI_{CBO}ICBO)
- ICBOI_{CBO}ICBO represents the current flow from the collector to the base while the emitter is open circuited.
- ICBOI_{CBO}ICBO is typically very small compared to ICI_CIC (microamperes vs. milliamperes) and can be neglected for most low- and mid-power applications.
- ICBOI_{CBO}ICBO is a significant factor to consider in high-power transistors.
- When IE=0I_E=0IE=0, the collector current is equal to ICOI_{CO}ICO.
In Summary
- The common-base configuration is one way to utilize a transistor.
- Common-base amplifier characteristics are complex and depend on operation region.
- Understanding the characteristics is crucial to choosing the right transistor and configuration for a specific application.
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Description
Explore the common-base configuration in transistors, where the base terminal is connected to both the input and output. This quiz covers key concepts such as current relationships, input and output characteristics, and the influence of biasing voltage sources. Test your understanding of this unique transistor configuration!
