Panasonic SA-HT640WP, Service Manual

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8.3. Class-D Amplifier
8.3.1. How are digital amplifiers different?
A digital amplifier incorporates a switching output stage that operates according to a principle known as pulse width modulation
(PWM). In contrast to the low-frequency control signal used in a conventional analog amplifier output stage, the switching output
stage of a digital amplifier is controlled by a high-frequency digital signal. The high-frequency digital signal is a PWM signal, in
which the music is modulated into a fixed-frequency carrier signal. In a digital amplifier, the modulation process is based on a digital
pulse code modulated (PCM) representation of the music signal (or other signal that needs amplification) from a CD player, a DVD
player, or some other device.
8.3.2. What are the advantages of digital amplification technology?
· High power efficiency, i.e., smaller heat sinks and/or no fan required
· Compact (reduced PCB area)
· Low weight (reduced transformer size)
· Good sound quality (low signal distortion/THD)
8.3.3. Why is the digital amplifier so efficient?
A class-D amplifier is one in which the output transistors are operated as switches. When a transistor is off, the current through it
is zero. When it is on, the voltage across it is small, ideally zero. In each case, the power dissipation is very low.
8.3.4. Does the “D” in class-D mean DIGITAL?
No. This is not correct because the operation of the class-D amplifier is based on analog principles. There is no digital coding of
the signal. Before the advent of the class-D amplifier, the standard classes were class-A, class-AB, class-B, and class-C. The “D”
is simply the next letter in the alphabet after “C.” Indeed, the earliest work on class-D amplifiers involved vacuum tubes and can
be traced to the early 1950s.
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SA-HT640WP / SA-HT640WPC