A perfect example is a BJT amplifier circuit, using only a single transistor and a pair of resistors (as shown in Figure 1). Paradoxically, it's often the circuits that appear to be the simplest that cause the most problems. Some circuits are easy and don't require much more than Ohm's law, while others seem a great deal harder. But it results in a smooth curve display.There are many things about transistors that confuse the beginner and no-so-beginner alike. I selected 2000 points per decade, which is over-doing it. Here's an example so that you won't have any remaining questions about what I just wrote, above:Īnd finally, here's a slightly fancier way to go. Spice will then parameterize your BJT model and perform a run for each step, which you control. You can then just focus on changing BF with the new model. If you include "ako:" and a starting model name then you won't have to specify all the parameters, as they will be defaulted to the specified model. STEP (this is not the only way, but just one way.) You can then use. To run a parameter sweep, I usually just use. Kloosterman which is an extensive PDF on their modeling approach. One of them is The Mextram Bipolar Transistor Model, G. But if you drill down to the Documentation page you will see multiple useful links. And finally, if you want the newest, best on the topic then see the most exquisite transistor model. Another good source to read is Chapter 14 on HSPICE's BJT modeling. If you go there, you can start on page A2.11. Lawrence Nagel's thesis, Spice2: A Computer Program to Simulate Semiconductor Circuits, is a good start. That said, you are allowed to study the models used and decide which of the parameters you want to control and over what range. You only get to bound the inputs to the simulation, not the outputs of it. You don't get to bound calculation results. Similarly, you don't get to tell Spice what you want for the range of the final computed forward beta. And that will almost always have the desired effect for any legitimate desire.īut, for example, you don't get to tell Spice over which range of voltage gains you want to run a simulation for a common emitter circuit design. You don't get to specify the resulting forward beta. Actually, pretty much everything matters in the end. ![]() There's also ISC, ISE, NC, NE, IKF, IKR, VAF, RE, RB, and RC to name still more that may have varying impacts depending on circumstances. Note that while BF is one of the BJT model parameters used in this process, it is not the only one that directly impacts the final results. Those results can be used to then derive the resulting forward beta. After time, and in comparison with some settable "stop when the changes from one step to the next are smaller than this amount", Spice will settle out and give you some results. In modeling a BJT's DC operating point, the actual forward beta is the result of iterated numerical circuit calculations where the linearized operating point of the BJT is repeatedly recomputed at each step and then re-applied to generate the next step's results. How can I obtain a BF, that corresponds to a change in beta of say 100 to 300? Unfortunately, I can only sweep over BF, and cannot find beta_F in the spice model. ![]() I want to run a parameter sweep to see how the bias point of an emitter circuit changes over the variable "DC forward current gain beta". ![]() But I cannot find out, how beta_F exactly relates to BF. In Multisim, I see BF for a 2N3904 defined as "ideal maximum forward beta". ![]() So If I understand correctly, BF is beta_F plus additional modelling. Then I read that the BF SPICE parameter is similar but not the same as beta_F.īF seems to be a parameter of the Gummel-Poon model which models the current gain by using beta_F (which is considered indpendant of temperature and emitter current) and then (using other spice parameters) add that dependencies. It seems those symbols all used to describe the same thing (correct me if I am wrong) As far as I understand, the BJT (bipolar junction transistor) DC forward current gain in common emitter configuration is given by
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |