![]() in the common base stage the input resistance at the emitter node is re=1/gm. There is only one case, where it makes sense to write re=1/gm. Hence, it is not a resistive element at all. The quantity gm is a "transconductance" and it does NOT describe the current-to-voltage relation between two nodes - and the same applies, of course, to the inverse 1/gm. The quantity 1/gm has "ohms" as unit (because it is the inverse of a conductance) but, in fact, it is not a resistive element at all. because they have read this somewhere) that the term re is something like a dynamic emitter-base resistance. My suggestion: Forget the term re and always use 1/gm instead of re. The term re does NOT represent any resistance between the nodes E and B. I don't quite understand how they represent the same thing aka the "dynamic resistance between the base and emitter terminals". Is it about where we look at the base from? They are both the dynamic resistance between the base and emitter terminals in my mind. I mean their definitions are same but yet they are different things. Even though the formulas yield this relation between r e and r π, I don't quite understand how they represent the same thing aka the "dynamic resistance between the base and emitter terminals". You might think what is my question here. Since there Ic = Ib × β this yields to r π = β × r e Secondly r π is the change in Vbe with respect to a change in Ib. So what I understand is that r e is the change in Vbe with respect to a change in Ic. It is the slope of the Ic Vbe plot at a fixed bias collector current i.e: g m=∂Ic/∂Vbe. ![]() ![]() I know the concept of transconductance g m. They both represent the dynamic resistor between the base and the emitter terminals.īut I read that they are different by a factor of β as: When comparing characteristics between DC current gain and small-signal current gain, it's best to keep in mind the differences between hFE and hfe.In BJT small-signal models there is both r e and r π parameters. It varies according to operating conditions. Conclusionīeta is not a fixed value when moving from one bipolar junction transmitter part to another. It's important to remember that beta can vary dramatically from one BJT part number to another. That's why you may see both forms of the term on the same datasheet with completely different numbers. The "BR" symbol means reverse active mode while the "BF" symbol refers to a forced situation in which the external circuit rather than the transistor imposes control.įurthermore, some people confuse "hFE" with "hfe." Lowercase letters are used for small-signal quantities while uppercase letters reflect large-scale quantities. IC stands for collector current while IB stands for base current.īeta can also be understood as the IC-to-IB ratio in the forward active mode when the "BF" symbol is used. H stands for hybrid, F stands for forward gain and E means common emitter. For example, It's common to find the symbol hFE instead of the "B" symbol for beta on BJT datasheets. The problem that many technicians face is that manufacturers have helped create confusion between certain terms. ![]() The device has two junctions and three terminals (base, emitter and collector).īeta can be detected for both small and large scale operations. ![]() The basis of a bipolar junction transistor is a connection between two diodes that generate a third layer of the transistor. Here are some essential terms related to BJT betas and why they create confusion. Beta reflects the proportionality between the base current and the collector current of a BJT set at the forward active mode. It's important to measure its beta, which is the gain or amplification factor of a transistor. A bipolar junction transistor (BJT) is a semiconductor device that can be used as an electrical switch or a switch to amplify a signal. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |