# Do transistors naturally have resistance on base, collector, and emitter?

I'm using a circuit simulation app called EveryCircuit, and for the npn transistor settings it has forward beta, reverse beta, base resistance, collector resistance, and emitter resistance. I'm a bit confused because I've only heard of alpha gain, beta gain, and voltage drop as parameters of a transistor. I'm assuming that forward and reverse beta are referring to the gain, but I'm not sure why they give settings for the resistance?

• There is Ohmic resistance between the leads, through to the wire bond and into the die. The silicon doping prior to the active regions adds more. Typically, the base has a somewhat higher resistance (about an order or two higher) than the other two leads. It's not a lot. Maybe $10-20\:\Omega$ for the base for a small signal device. The earliest Ebers-Moll model didn't include them. It wasn't until version 2 (EM2) that these parasitics were added. – jonk Sep 20 '19 at 14:43
• so if I'm writing a schematic should I add these in as resistors? – buckithed Sep 20 '19 at 14:54
• A spice program includes parameters for these values, so you do not need to add them. If you writing your own sim program and schematic editor and your transistor model is just a version 1 of the Ebers-Moll model, then you may want to make them explicit. The level 1 version of 3 equiv. Ebers-Moll models doesn't include them. It wasn't until the level 2 modifications that they were added. It may also help you to read the different regions (I, II, and III) of operation for a BJT here. – jonk Sep 20 '19 at 15:03
• @jonk, your comments should be posted as an answer. – The Photon Sep 20 '19 at 15:29
• @ThePhoton Then I'd have to actually work. (I'd need to draw out the behavioral diagram, the original level 1 model, the additions of the level 2 model [and probably what was added in the level 3 model to delineate the boundaries of the level 2 model], and some further explanatory text.... I don't have time for that right now.) Maybe later? – jonk Sep 20 '19 at 15:32