ch2 lecture 3

Low frequency and lower 3 db frequency
Here the circuit will analyse with existing of emitter capacitance and coupling capacitance, and finding that the coupling capacitor give a pole and zero, and the emitter capacitor also give a pole and zero (this is offcourse in bipolar transistor), and the emitter capacitor pole is related with the zero of the same capacitor. For FET transistor the source capacitor also give a pole and zero with a relation between them, and the coupling capacitor did not affected since the input impedance of the FET is very large. After the analyse the finding of the lower 3db frequency is done by hand calculation or by sketching the bode plot.
The above analysis of the frequency behavior of single-stage circuits indicates the complexity that can arise even with simple circuits. The complete analysis of the frequency response of multistage circuits with many capacitive elements rapidly becomes very difficult and the answers become so complicated that little use can be made of the results. For this reason approximate methods of analysis have been developed to aid in the circuit design phase, and computer simulation is used to verify the final design.