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GMiaille
Class G/H shouldn't have a higher distorsion than Class AB or it means that the ...
Avatar Engineer
Class D works well when you know what you're doing.
Do Class G/H amplifiers deliver higher audio quality and low power consumption?
Helmut Theiler, Herbert Lenhard, Horst Gether, austriamicrosystems
8/19/2010 12:41 PM EDT
In traditional hi-fi systems, the specifications of audio amplifiers emphasized audio quality, but paid less regard to the level of power losses. As the portable hi-fi sector of the audio industry has grown, however, the shortcomings of traditional amplifier devices – in particular, their inefficiency – have come to the fore.
Traditionally, audio playback equipment has used so-called Class AB amplifiers, which generate little distortion and consequently produce high audio quality. The operation of a Class AB amplifier, however, explains its relatively low efficiency: the internal voltage of the amplifier drops as the output voltage drops. The amplifier dissipates excess power across its transistors, and so as the power output to the speakers drops, the efficiency of the system declines.
In mains-powered hi-fi equipment this is not a fundamental problem; in battery-powered audio devices such as mobile phones and MP3 players, it most certainly is, as the audio amp takes a significant portion of the system’s power budget. In the case of MP3 players, the proportion of total power consumption attributable to the audio amplifier can be as high as 80 percent.
As a result, audio equipment designers have been looking for enhancements to the Class AB topology. The question that this article addresses is, are worthwhile power savings achievable through implementing a newer technology such as Class G or Class H? And if a system designer adopts a Class G or Class H amplifier, are the differences in power consumption between different implementations of Class G or Class H large enough to affect the overall power budget?
About the authors
Horst Gether is Product Manager, Consumer and Communications Business Unit; Herbert Lenhard is a Design Engineer in CON MS Design Department; and Helmut Theiler is a Design Engineer in CON Backlight Design, all with austriamicrosystems.
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kdboyce
8/19/2010 3:22 PM EDT
I understand that the intent of the article was to describe Class G/H characteristics on power consumption. The article did not provide any information as to how music or other source sounded when listened to in earpieces or headphones. Just graphs.
In practice, the supply adjustments are difficult to make smoothly for all types of audio input, and you can sometimes hear volume shifts that you wouldn't hear in a Class A/B amp. For listeners very familiar with music, this could be annoying. For the average user who uses their portable device for convenient and casual playback of MP3 music, it may not be a problem. For cell phone voice communication, it is not a problem.
Human hearing is very sensitive, and to have the potential for shifts in volume to be right in the ear canal via earpieces would, for me, be very annoying.
But the techniques do save power for sure.
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Qadeer
8/26/2010 10:11 AM EDT
This might be true for Class-G as change in supply is discrete but for Class-H I don't see any problem in tracking. It mostly depends upon bandwidth of DC-DC converter. Considering the 20KHz audio bandwidth, a switching converter with 100KHz bandwidth should be good enough for seamless tracking(which corresponds to 1-2MHz of switching frequency). Could you please elaborate more on what exactly you meant by different types of audio inputs?
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Frank Eory
8/19/2010 5:23 PM EDT
I thought it was an ok article for a marketing-oriented piece. Like most things, the devil's in the details. A good Class G or H design requires careful coordination between the amplifier designer, the voltage regulator designer, and the person who is putting together the overall feedback system.
The authors pointed out the threshold voltage limitation and the fact that greater efficiency can be achieved with low VT devices, but they didn't mention that the slew rate of the regulator can also be a limiting factor -- thus the importance of close cooperation between the designers working on each piece and on the integrated system.
When done correctly, a Class G or H amp is indistinguishable from a Class AB on every audio parameter of interest. There should be no way to tell which is which except by measuring efficiency. I was disappointed that they didn't emphasize the efficiency improvements more than just with one little graph. For portable audio devices, the efficiency gain of Class G or H is a huge deal that translates into extra hours of playback time.
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azifsaly
9/7/2010 12:32 AM EDT
Do you really feel that the ClassG/H parameters would be same as a Class AB one ? The distortion of a G/H amp is higher .
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Jimelectr
8/22/2010 1:32 AM EDT
I would like to see a comparison of efficiency of Class AB Class G/H and Class D. Now, I haven't investigated how feasible Class D is for low-voltage, portable applications, but theoretically its efficiency approaches 100%, something Class AB is incapable of doing. Interesting that Class G/H is also being used for RF/microwave power amplifiers at roughly 5 orders of magnitude higher frequency!
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azifsaly
9/7/2010 12:46 AM EDT
The efficiency of a G/H amplifier depends on the kind of music or tone played.Neverthless I would say Class D is the efficient of all .
I would go by the rule that in portable devices ,use Class D for higher power output requirements and Class G/H for moderate and low power requirement.
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kendallcp
8/22/2010 12:34 PM EDT
I concur with Feory here. Audio amplifier design is certainly well enough understood these days that the forward performance of a class G headphone or power amp should be indistinguishable from that of older topologies, by the vast majority of listeners. And the power consumption advantages are well understood and easy to calculate, no mystery there.
These higher-efficiency linear amplifiers are often preferred by designers who've had their fingers burned (though probably not literally!) by class D amplifiers and their associated switching artefacts. Quiescent power dissipation is also a weak point down at this low power level. Many vendors are heading towards class G as a good compromise between classical linear designs and class D designs.
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Avatar Engineer
9/8/2010 11:02 PM EDT
Class D works well when you know what you're doing.
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GMiaille
9/9/2010 4:08 PM EDT
Class G/H shouldn't have a higher distorsion than Class AB or it means that the PSRR of the audio amplifier is not right.
Class D for headphones looked interesting but had issues too (EMI with headphone wires and also common mode). At low output power, the class D will also need a variable and efficient power supply to be able to compete with class G/H. The comment of azifsaly pretty much summarizes which topology to use and when.
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