Comparison of CE, CB and CC Configurations: It is useful to study the variation of A_{I}, A_{V} and R_{i} with change in load resistance R_{L} for each of the three configurations.

Similarly, we may study variation of R_{0} with change of source resistance R_{S}. Figure 1, 2 and 3 plots for each of the three configurations, current gain A_{I}, voltage gain A_{V} and input resistance R_{i} respectively as function of load resistance R_{L} for the typically transistor whose h-parameters are given in Table 4.1.

From these curves we get the following information:

**(A) CE Amplifier**

A_{I} is high for

A_{V} is high for usual values of R_{L}. Typical value of R_{L} is

R_{i} is medium (about ) and varies nominally with variation of R_{L}.

R_{0} is moderately high and varies appreciably with variation of R_{S}.

Uses: CE amplifier is capable of providing moderately high values of both A_{I} and A_{V}. Hence it is popularly used.

Table 1 Approximate Conversion Formulas for h-parameter | |

**(B) CB Amplifier**

A_{I} < 1 and its magnitude decreases with increase of R_{L} beyond , reaching a value of about 0.2 for .

A_{V} is high for usual value of R_{L}.

R_{i} is low (), being lowest of all the three configurations.

R_{0} is high , being highest of all the three configurations.

Uses: CB amplifier is not used as an amplifier for providing voltage or current gain. It is used only:

- For matching a very low impedance source to the high input impedance of the main amplifier.
- As a noninverting amplifier with A
_{V}> 1. - For driving a high impedance load.
- As a constant current source for use in a sweep (time-base) voltage generator or to charge a capacitor linearly with time.

**(C) CC Amplifier**

A_{I} is high, almost equal to that of CE amplifier for

A_{V} <1

R_{i} is high, being highest of all the three configurations.

R_{0} is low, being lowest of all the three configurations.

Uses: It is used as a buffer amplifier between a high impedance source and a low impedance load.

Table 2 gives the value of A_{I}, A_{V}, A_{P}, R_{i}, and R_{0} for a typical transistor (h-parameters given in table 1) for all the three configurations using and . Actually, these values of A_{I}, R_{i}, A_{V}, R_{0} and A_{P} are picked up randomly.

Table 2: Performance Schedule of Typical Transistor in CE, CB and CC Configurations | |||

Quantity | CE | CB | CC |

A_{I} |
-45 | 0.98 | 46 |

A_{V} |
-172 | 169 | 0.99 |

A_{P} |
7817 | 166 | 46 |

A_{i} |
|||

R_{0} |