Introduction
1. Background
This is the first applet seriously attempting to provide a visual simulation of a transistor amplifier.
The circuit is a Common-Emitter amplifier where the bipolar transistor operates in the Active region.
The upper-left diagram shows the carrier concentration profile in the Base region, electrons (blue) in the conduction band and holes (red) in the valence band. The blue and red colored regions represent the carrier concentration profile. The blue dots the electrons, moving-into/out-of the Base region, shown in the conduction band (above Ec, the conduction band edge). The red dots are holes, moving in and out of the Base. The number of dots is roughly proportional to the logarithm of the current value.
The lower-left diagram is the circuit, containing a bipolar transistor, resistors Rb=10k and Rc=5k, the power supply Vcc and a voltage signal. You can control the signal voltage by the arrow-control at the bottom of the applet.
The upper-right diagram is the output characteristic (Collector current Ic vs. Collector-Emitter bias Vce) of the transistor. The green line is called the (DC) Load Line: Vce = Vcc - Ic * Rc. If the blue curves represent the transistor's internal property (output characteristic), then the green line is the circuit property, external to the transistor (load line since it depends on the load resistance, Rc).
The lower-right region lists the various current values. First subscript is the transistor region, (e=emitter, b=base, c=collector), and the second subscript is the carrier (n=electron, p=hole). For example, Ien is the emitter current due to electron.