IMPEDANCE CHARACTERISTICS OF AMPLIFIER CONFIGURATIONS
5-57. You have seen the importance of impedance matching the stages in an electronic
device. Next, we will look at the impedance characteristics of an amplifier. The input and
output impedances of a transistor amplifier depend upon the configuration of the transistor.
You have already been introduced to the CE, CB, and CC transistor configurations. Figure
5-13 shows examples of these configurations and their impedance characteristics.
NOTE: Only approximate impedance values are shown. This is because the
exact impedance values will vary from circuit to circuit. The impedance of any
particular circuit depends upon the device (transistor) and the other circuit
components. The value of impedance can be computed by dividing the signal
voltage by the signal current.
5-58. The CE configuration provides medium input impedance and medium output
impedance. The CB configuration provides low input impedance and high output
impedance. The CC configuration provides high input impedance and low output
impedance. The CC configuration is often used to provide impedance matching between
high output impedance and low input impedance.
23 June 2005