WHAT IS A PULSE AMPLIFIER?
In simple terms, an amplifier is a device that increases the magnitude of the output signal without changing other waveform parameters such as the frequency or wave shape. They are commonly plugged-in electronic circuits to perform various functions as per the requirement of the electronic system. However, a Pulse Amplifier is an electronic amplifier device or equipment designed to increase the magnitude of power, current, or voltage of an input signal. In other words, the power of the input signal is increased to a significantly high level to drive output devices like audio systems, broadcasting devices, wireless communication devices, etc. Pulse amplifier is widely used as the last input device in electronic amplifier chain whose output is directly fed to the final output device of the electronic circuit. There are three major categories of amplifiers based on the output;
- Voltage Amplifier - As the name suggests voltage amplifier is designed to increase the magnitude of output voltage waveform concerning input voltage waveform. At the same time magnitude of the output current may be greater or smaller than the input current.
- Current Amplifier - It works like the voltage amplifier where the magnitude of the output current waveform concerns the input current waveform. At the same time magnitude of the output voltage may be greater or smaller than the input current.
- Power Amplifier - In a power amplifier, the product of voltage and current at the output is greater than the product of voltage x current at the input. As mentioned above, either voltage or current may be less at the output than at the input, but the product of the two will be significantly high.
This article will focus on the basics of pulse power amplifiers. The pulse power amplifier is further classified into various categories, which will be explained in detail below.
CLASSES OF PULSE POWER AMPLIFIER
Designing of any Pulse amplifier circuit is solely governed by its application & desired result since the output characteristics of each circuit configuration differ entirely from one another. To achieve the desired output characteristics of the Pulse amplifier circuit, a wide range of Pulse power amplifiers are used. They can be majorly categorized as
- Power amplifiers designed and constructed with an intent to amplify analog signals which fall under Class A, B, AB, or C.
- Power amplifiers designed with an intent to amplify Pulse Width Modulated digital signals which fall under Class D, E, F, etc.
However, while designing power amplifier circuits, the most common choice of a power amplifier is the ones with Class A, Class B, Class AB, or Class C. These individual power amplifiers will be explained in detail.
- Class A Pulse Power Amplifier - The design of the Class A pulse power amplifier is extremely simple as it carries out amplification of the entire analog waveform (including positive high and negative lows) with the use of a single transistor.
The simplistic design makes it a preferred choice while designing a power amplifier circuit. Still, the use of a single transistor generates a significant amount of heat, which reduces the efficiency to 25% under standard configuration and even 50% when connected to transformer-coupled configuration. To overcome the shortcomings of the Class A power amplifier, the Class B Pulse power amplifier was introduced. But the use of any class of amplifier is solely guided by its application.
- Class B Pulse Power Amplifier - As mentioned, the introduction of the Class B power amplifier addressed the efficiency and heating concerns faced in earlier class amplifiers. In this case, two complementary transistors are introduced. One set of transistors is operating amplification of positive half of waveform whereas, the second set of the transistor controls the negative half of waveform which later combined and the entire signal is amplified.
The two-transistor design significantly enhances the Class B power amplifier's efficiency, making it an ideal choice for battery-operated FM radios and a transistor radio. However, the concern of distortion was noticed at the time of combining two half halves, which urged the need to develop another amplifier that could offer benefits of both amplifiers.
- Class AB Pulse Power Amplifier - As the name suggests, Class AB Pulse power amplifier is the combination of Class A and Class B power amplifiers. The intent behind designing this class of power amplifiers was to address the heating & efficiency issues of Class A power amplifiers and distortion issues faced in Class B power amplifiers. Its construction consists of two complementary transistors responsible for amplifying individual halves of signal, unlike Class B power amplifier. Still, the difference is the combined use of diodes & resistors, which offer stability in voltage and reduce distortion of the waveform. This unique construction offers better efficiency and a significant reduction in component heating compared to earlier variants.
- Class C Pulse Power Amplifier - The basic design of the class C power amplifier provides better efficiencies but at the cost of low amplification quality due to lesser conduction angle. Lesser conduction angle is directly proportioned to higher distortion, thus making Class C pulse power amplifier an ideal device for high-frequency oscillators and amplification of Radio Frequency signals. Construction difference of Class C pulse power amplifier generally includes a tuned load whose basic function is to filter and amplify input signals of a particular frequency. At the same time, waveforms of other frequencies are suppressed. Such a Class C pulse power amplifier construction allows the inbuilt transistor or active element to conduct only when the input voltage crosses a certain threshold. This unique feature reduces the power dissipation and increases the overall efficiency of the amplifier.
HOW DOES THE PULSE AMPLIFIER WORK?
The working principle of pulse amplifier can be elaborated as high or low voltage magnitude pulse is generated through pulse source commonly referred as "pulse generator". These generators are capable of generating signal pulses at variable width and frequency. On receipt of high or low magnitude pulse depending upon the application, the controller on Pulse amplifier regulates the range of energy to be supplied at the output of Pulse amplifier. It ensures that energy generated is within the upper and lower ranges regulated by the pulse amplifier's controller.