# What is RB in this CE circuit?

I'm working through this handout I3.PDF to help me understand feedback in common emitter amplifiers. (The author does not reveal his/her name in the PDF and so I can't ask them directly.) They show a common emitter circuit at the top and a small-signal model just below it. What expression defines the resistance $$\R_B\$$ in the model?

I'm imagining two possibilities. First, it might be be some combination of $$\R_1||R_2\$$. This doesn't seem correct. In the upper schematic $$\R_1\$$ appears between base and ground whereas $$\R_2\$$ appears between $$\V_{CC}\$$ and the base. But in the small-signal equivalent, $$\R_B\$$ appears only between base and ground. The second possibility is that it is simply $$\R_1\$$ alone. With us only considering small-signal (AC) voltages, $$\V_{CC}\$$ would appear as ground and so we ignore it and the resistor directly connected to it? Both of my guesses seem flawed.