Class A and Class AB amplifiers have long dominated the amplifier marketplace. These
purely analog devices have low power efficiency, and most integrated circuit Class AB
amplifiers fall short of true high-fidelity audio quality. Another class of amplifier, Class D,
solves the efficiency problem by using switching pulse-width modulation (PWM) technology.
However, this produces audio output quality that is inferior to Class A or AB, so efficiency is
gained at the expense of signal fidelity. As a result, these amplifiers are generally used only
in low-frequency subwoofer applications where the audio fidelity performance level of PWM
amplifiers is acceptable. The “Holy Grail” of amplification: high audio quality and high power
efficiency in a single technology has long eluded the market.
Tripath Technology has developed a category of digital audio power amplifiers using a
unique technology. Tripath amplifiers use a completely new proprietary method of Digital
Power Processing™ that provides superior performance to conventional methods of
amplification. For the first time, both high signal fidelity AND high power efficiency can be
achieved with the same technology. Tripath refers to this DPP™ based amplifier as a
Class T design. The underlying technology of Class-T does not use PWM and is not a pure
analog approach (Classes A and AB). It combines the benefits of both with a completely
new approach.
Tripath’s Class T amplifiers are the first application of this breakthrough approach. Class T
amplifiers provide the signal fidelity of sophisticated discrete-component linear Class A and
AB designs, while offering high power efficiencies and the potential to need less exotic
engineering to achieve high-end audiophile performance. These amplifiers also reduce cost
for amplifier overhead at high power levels (such as power supply, filtering, and heat
venting). Class T provides power conversion efficiencies of 80 percent to more than 90
percent, which is equal to or better than Class D amplifiers. Customers no longer have to choose between optimizing signal fidelity or efficiency. Both
can now be achieved with Class T technology.
Instead of using PWM, Tripath Class T amplifier processors use proprietary algorithms and
techniques to create the modulation that drives the switching transistors. A Class T
amplifier’s processors learn the characteristics of the output transistors. Then, based on the
analog input signal, they switch the output transistors with exactly the right timing to
eliminate Class D PWM problems: transistors not being perfect switches, ground bounce,
output transistor mismatches, dead-time distortion and residual energy from the oscillator in
the audio band. The result is a high power efficiency, audiophile-quality audio amplifier, a
Class T amplifier.
If one were to compare the waveform before the output filter of a Class D PWM amplifier to
a Tripath Class T amplifier, some significant differences would be evident. The waveform
for a Class D PWM amplifier would be a pulse-width varying digital signal at the fixed, 100-
200kHz, frequency of the triangle wave generator. The waveform for a Tripath Class T
amplifier would be a complex digital waveform of varying frequency. A Class T amplifier
switches the output transistors in a fashion similar to spread spectrum technology, at a
varying rate up to 1.5 MHz and averages 600kHz to 700kHz.
What this difference means, in addition to significantly better audio quality, is that a Tripath
Class T amplifier can use lower-cost inductors and capacitors for its output filter while
obtaining the same amount of filtering as a Class D PWM amplifier. A Class T amplifier
also has lower electromagnetic emissions than a Class D PWM amplifier broadening its
potential application.
But the true test of any amplifier is ultimately how it sounds. Class T amplifiers have been
designed with the latest advances in adaptive signal processing technology, while remaining
true to the “warm” sounds that listeners have come to expect from their traditional analog
products. With Tripath Technology, listeners can have the best of both worlds: high fidelity
sound AND high power efficiency.
(Extract from CLASS-T DIGITAL AUDIO AMPLIFIER TECHNOLOGY OVERVIEW, by Tripath Technology, Inc.)