4.1 Introduction
When the output to be delivered is large, much greater than m W range and is of the order of few
watts or more watts, conventional transistor (BJT) amplifiers cannot be used. Such electronic
amplifier circuits, delivering significant output power to the load (in watts range) are termed as
Power Amplifiers. Since the input to this type of amplifier circuits is also large, they are termed as
Large Signal Amplifiers. In order to improve the circuit efficiency, which is the ratio of output
power delivered to the load Po to input power, the device is operated in varying conduction angles of
3600
, 1800 less than 1800 etc. Based on the variation of conduction angle, the amplifier circuits are
classified as Class A, Class B, Class C, Class AB, Class D, and Class S.
4.1.1 Power Amplifier
Large input signals are used to obtain appreciable power output from amplifiers. But if the input signal
is large in magnitude, the operating point is driven over a considerable portion of the output characteristic
of the triinsistor (BJT). The transfer char~cteristic of a transistor which is a plot between the output
current Ie and input voltage V BE is not linear. The transfer characteristic indicates the change in ic when
Vb or IB is changed. For equal increments of VBE, increase in Ie will not be uniform since output
characteristics are not linear (for equal increments ofVBE, Ie will not increase by the same current). So
the transfer characteristic is not linear. Hence because ofthis, when the magnitude of the input signal is
very large, distortion is introduced in the output in large signal power amplifiers. To eliminate distortion
in the output, pushpull connection and negative feedback are employed.
ผมแปลภาษาอังกฤษไม่เก่งแถมมันเป็นศัพท์ช่างด้วยครับคำกลัวแปลแล้วไม่ถูกอ่ะครับช่วยผมแปลหน่อยครับ
When the output to be delivered is large, much greater than m W range and is of the order of few
watts or more watts, conventional transistor (BJT) amplifiers cannot be used. Such electronic
amplifier circuits, delivering significant output power to the load (in watts range) are termed as
Power Amplifiers. Since the input to this type of amplifier circuits is also large, they are termed as
Large Signal Amplifiers. In order to improve the circuit efficiency, which is the ratio of output
power delivered to the load Po to input power, the device is operated in varying conduction angles of
3600
, 1800 less than 1800 etc. Based on the variation of conduction angle, the amplifier circuits are
classified as Class A, Class B, Class C, Class AB, Class D, and Class S.
4.1.1 Power Amplifier
Large input signals are used to obtain appreciable power output from amplifiers. But if the input signal
is large in magnitude, the operating point is driven over a considerable portion of the output characteristic
of the triinsistor (BJT). The transfer char~cteristic of a transistor which is a plot between the output
current Ie and input voltage V BE is not linear. The transfer characteristic indicates the change in ic when
Vb or IB is changed. For equal increments of VBE, increase in Ie will not be uniform since output
characteristics are not linear (for equal increments ofVBE, Ie will not increase by the same current). So
the transfer characteristic is not linear. Hence because ofthis, when the magnitude of the input signal is
very large, distortion is introduced in the output in large signal power amplifiers. To eliminate distortion
in the output, pushpull connection and negative feedback are employed.