Intrinsic resistance of a transistor

In summary, the conversation is about finding the intrinsic emitter resistance of a bipolar transistor. The speaker tried modeling circuits in SPICE but was unable to find the correct value for the resistor. The professor mentioned that the resistance can be found using the change in collector voltage and change in emitter voltage, but this doesn't make sense to the speaker. Another person suggested an equation for finding the resistance, but the speaker is looking for another method using delta Vc and delta Ve.
  • #1
adiman1984
2
0
In my circuits class we were talking about bipolar transistors and our prof. mentioned that every bipolar resistor has an intrinsic emitter resistor. So, I tried modeling a couple of circuits in SPICE to see if I can replace the transistor with another circuit (voltage source, current source, and the intrinsic resistor). However, I never got to that point, because I could not find the correct value of this resistor. In class he just said that we need the change in collector voltage (delta Vc) and change in emitter voltage (delta Ve) to figure it out. That doesn't make any sense to me. Don't you need a current to find that?
Does anyone have an explanation of how to find the intrinsic emitter resistance of a bipolar transistor?

Thanks
 
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  • #2
re = Vt/Ie.

Vt = kT/q; k = 1.38e-23 joule/Kelvin, T = temperature in Kelvin, q = 1.602e-19 coulomb.

Ie = dc or bias value of emitter current

Claude
 
  • #3
Claude,

Thanks for your answer. This will help me to double check if I'm right with my approximation. However, there should be another way to get to the intrinsic emitter resistance.
According to the attached picture, the resistance can be approximated with delta Vc and delta Ve (the deltas are obtained by sweeping Vb over a certain range).
Any ideas how this is done?

Thanks
 

1. What is intrinsic resistance of a transistor?

Intrinsic resistance of a transistor refers to the inherent resistance that is present within the transistor itself. It is a result of the material properties and physical structure of the transistor.

2. What factors affect the intrinsic resistance of a transistor?

The intrinsic resistance of a transistor can be affected by the doping concentration, material properties, and physical dimensions of the transistor. It can also be affected by temperature and the operating conditions of the transistor.

3. How does intrinsic resistance impact the performance of a transistor?

The intrinsic resistance of a transistor can impact its performance by affecting its gain, power dissipation, and frequency response. A higher intrinsic resistance can result in lower gain and slower switching speeds.

4. Can the intrinsic resistance of a transistor be reduced?

Yes, the intrinsic resistance of a transistor can be reduced by optimizing the doping concentration, material properties, and physical dimensions of the transistor. It can also be reduced by using different materials and technologies, such as high-electron-mobility transistors (HEMTs) or heterojunction bipolar transistors (HBTs).

5. How is intrinsic resistance different from extrinsic resistance?

Intrinsic resistance is the inherent resistance of a transistor, while extrinsic resistance is caused by external factors such as the connections and layout of the circuit. Intrinsic resistance is an inherent property of the transistor, while extrinsic resistance can be controlled and reduced through circuit design.

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