Example: Collector-to-base Biased Bipolar Amplifier
Figure 1 (top right) shows a bipolar amplifier with feedback bias resistor Rf driven by a Norton signal source. Figure 2 (left panel) shows the corresponding small-signal circuit obtained by replacing the transistor with its hybrid-pi model. The objective is to find the return ratio of the dependent current source in this amplifier. To reach the objective, the steps outlined above are followed. Figure 2 (center panel) shows the application of these steps up to Step 4, with the dependent source moved to the left of the inserted source of value it, and the leads targeted for cutting marked with an x. Figure 2 (right panel) shows the circuit set up for calculation of the return ratio T, which is
The return current is
The feedback current in Rf is found by current division to be:
The base-emitter voltage vπ is then, from Ohm's law:
Consequently,
Read more about this topic: Return Ratio
Famous quotes containing the word biased:
“Scientists are human—they’re as biased as any other group. But they do have one great advantage in that science is a self-correcting process.”
—Cyril Ponnamperuma (b. 1923)