HT66FV1x0 Integrated Audio Amplifier Application Guideline
AN0486EN V1.10
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June 8, 2021
IC
IC
Class B
Crossover Distortion
Class AB Crossover
Distortion Eliminated
Q2 On
Q1 On
Q1 On
Vbe
Vbe
Class AB
Class D Principles
Class D amplifiers operate based on an MOS transistor on/off switching. Transistors can be
completely switched on or off in a very short time providing a relatively high efficiency. However,
this switching mode of operation adds distortion to the output signals. The Class D modulator is a
PWM modulator composed of a comparator and a triangle wave generator. The input signal is
filtered by an integrator to generate a corrected signal, which is used to modulate the triangle wave
to produce the modulated square wave output. A MOSFET driver is used for high power voltage
and current amplification after which the amplified digital signal is filtered by a low-pass filter to
restore the analog audio signal.
Class D
Modulator
MOSEFET
Driver
Low-pass Filter
Class D
Advantages and Disadvantages Comparison – Class AB Amplifiers vs. Other
Power Amplifiers
For Class AB, its efficiency is higher than Class A and its distortion is lower than Class B. The
operating mode of Class D is totally different from Class AB. In a Class D amplifier, some high
frequency harmonics will be generated therefore EMI will be greater. Class AB amplifiers have a
significant cost advantage over Class D amplifiers, because the latter are usually two or three times
the price of the former. In general, Class AB amplifiers have the advantages of higher efficiency, lower
distortion and lower costs, which make them the most widely used design in audio amplifier
applications at present.
Q1
RL
V+
V-
Q2
