On the basis of their biasing, with the help of appropriate diagrams, justify the uses
of Class A, AB and C amplifiers for various applications.
Class A Amplifier
Class A Amplifiers are the most common type of amplifier class due mainly to their simple design. Class A, literally means “the best class” of amplifier due mainly to their low signal distortion levels and are probably the best sounding of all the amplifier classes mentioned here. The class A amplifier has the highest linearity over the other amplifier classes and as such operates in the linear portion of the characteristics curve.
Generally class A amplifiers use the same single transistor (Bipolar, FET, IGBT, etc) connected in a common emitter configuration for both halves of the waveform with the transistor always having current flowing through it, even if it has no base signal. This means that the output stage whether using a Bipolar, MOSFET or IGBT device, is never driven fully into its cut-off or saturation regions but instead has a base biasing Q-point in the middle of its load line. Then the transistor never turns “OFF” which is one of its main disadvantages.
Class A Amplifier
To achieve high linearity and gain, the output stage of a class A amplifier is biased “ON” (conducting) all the time. Then for an amplifier to be classified as “Class A” the zero signal idle current in the output stage must be equal to or greater than the maximum load current (usually a loudspeaker) required to produce the largest output signal.
As a class A amplifier operates in the linear portion of its characteristic curves, the single output device conducts through a full 360 degrees of the output waveform. Then the class A amplifier is equivalent to a current source.
Since a class A amplifier operates in the linear region, the transistors base (or gate) DC biasing voltage should by chosen properly to ensure correct operation and low distortion. However, as the
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Design a zener regulated power supply to give 9.1V DC output with maximum load current of 50 mA. Assume that the minimum IZ required for proper functioning of zener diode is 5 mA, and the unregulated DC input is 12V. Indicate the value of RS
and power ratings of zener diode and RS.
Draw a half adder circuit using only NAND gates.
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Divide 11618 by 318. Express the obtained result in decimal number.