summary
● Amplifiers are electronic circuits used to increase the amplitude of an electronic signal.
● The transistor is used primarily as an amplifying device.
● The three transistor amplifier configurations are common base, common collector, and common emitter.
● Common-collector amplifiers are used for impedance matching.
● Common-emitter amplifiers provide phase reversal of the input–output signal.
● All transistor amplifiers require two voltages for proper biasing.
● A single voltage source can provide the necessary forward-bias and reverse-bias voltages using a voltage-divider arrangement.
● A voltage-divider feedback arrangement is the most commonly used biasing arrangement.
R4 ● A transistor amplifier can be biased so that all
or part of the input signal is present at the output.
● Class A amplifiers are biased so that the output current flows throughout the cycle.
● Class AB amplifiers are biased so that the output current flows for less than the full but more than half of the input cycle.
● Class B amplifiers are biased so that the output current flows for only half of the input cycle.
● Class C amplifiers are biased so that the output current flows for less than half of the input cycle.
● Coupling methods used to connect one transistor to another include resistance-capacitance coupling, impedance coupling, transformer coupling, and direct coupling.
● Direct-coupled amplifiers are used for high gain at low frequencies or amplification of a DC signal.