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Class D Switching Power Amplifiers and Power D/A conversion

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Old 13th September 2009, 11:58 PM   #21
wwenze is offline wwenze  Singapore
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You got me there, I was thinking of FM as radio talkshow broadcast, and didn't include its vast other applications.

Otherwise, seems like any further typing generates more confusion, I shall refrain.

P.S. I have to admit I made another mistake above, regarding the definition of sampling - the reduction of a continuous signal to a discrete signal, so analogue sampling as I typed above - guess this is another mine. Anyone going to pick on this?

Last edited by wwenze; 14th September 2009 at 12:00 AM.
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Old 14th September 2009, 02:18 AM   #22
Bernie7 is offline Bernie7  Singapore
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Pafi

Thanks for discussing.

According to you, Class D is neither analog or digital, it can be both.

Where does that leave us? Is there a third category for PWM?
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Old 14th September 2009, 08:23 AM   #23
Pafi is offline Pafi  Hungary
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Bernie!

You're welcome!

First of all: PWM is not equal to ClassD. Not every ClassD circuit uses PWM.

ClassD is not a signal, nor a circuit, it's a category, it is neither analog, nor digital. A given circuit of this category can be discussed wether it is analog or digital. For example these are digital: http://focus.ti.com/lit/sg/slyt312/slyt312.pdf but many others are analog, like: LM4651, UcD, etc...

wwenze!

In connection with your post I must agree:
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seems like any further typing generates more confusion
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Old 15th September 2009, 03:15 AM   #24
Bernie7 is offline Bernie7  Singapore
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Quote:
Originally Posted by Pafi View Post
Bernie!

You're welcome!

First of all: PWM is not equal to ClassD. Not every ClassD circuit uses PWM.

ClassD is not a signal, nor a circuit, it's a category, it is neither analog, nor digital. A given circuit of this category can be discussed wether it is analog or digital. For example these are digital: http://focus.ti.com/lit/sg/slyt312/slyt312.pdf but many others are analog, like: LM4651, UcD, etc...
We may have been on different pages in our discussion then Yes I know "Class D" is a category with the "D" an arbitrary letter assignment.

I had in mind UcD amps and such when I asserted that it was analog. I myself have a pair of UcD monoblocks. May I assume that the mainstream Class D amps are analog, eg those based on ICE, Spectron etc?

Which Class D consumer amps do you know of are digital? Why would they be classified under Class D, or, what specific distinguishing feature warrants this?
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Old 15th September 2009, 08:27 AM   #25
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Bernie7 View Post
May I assume that the mainstream Class D amps are analog, eg those based on ICE, Spectron etc?
no.
Any output that is a reconstituted version that comes from a chopped or switched waveform cannot be analogue
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Old 15th September 2009, 10:28 AM   #26
Pafi is offline Pafi  Hungary
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Quote:
Originally Posted by AndrewT View Post
no.
Any output that is a reconstituted version that comes from a chopped or switched waveform cannot be analogue
Why? Because you don't let it to be?

If it is not analog, then please tell me what is its resolution! What is the smallest change that is representable by PWM? The answer is: zero! Hence it is analog. (If it is a simple PWM.)

Bernie7!

Quote:
We may have been on different pages in our discussion then Yes I know "Class D" is a category with the "D" an arbitrary letter assignment.
I know, but you used the terms "PWM" and "ClassD" in the same meaning if I understand correctly.

Quote:
based on ICE, Spectron etc?
I don't know them. I don't buy ClassD amps, I build them.

Quote:
Which Class D consumer amps do you know of are digital?
For example:
http://www.tactlab.com/Products/T2/T2.html

Quote:
Why would they be classified under Class D
Because they are switch mode (=Class D) amplifiers. The output transistors has two states: fully open and fully closed. That's all.

Quote:
or, what specific distinguishing feature warrants this?
Officially digital means digital . If the manufacturer says it's digital, then it is (probably).

Your earlier question:
Quote:
In Class D PWM, does any manufacturer today reduce the signal to coded binary so that the usual digital error correction routines may be applied?
Error correction is pointless in this aspect. Digital error correction can correct only the errors occured in digital signal, but in a chip the probability of any digital error is negligible. In some amplifiers (and in many sound processors) analog signal is digitized in order to be able to feed into the digital signal chain, but this has nothing to do with digital error correction. (Exept if somebody want to transmitt the signal.)

Last edited by Pafi; 15th September 2009 at 10:35 AM.
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Old 15th September 2009, 12:49 PM   #27
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Pafi View Post
What is the smallest change that is representable by PWM? The answer is: zero! Hence it is analog. (If it is a simple PWM.)
"zero" is clearly either an exageration or not true.
Which?
What is an inherent characteristic of an analogue transmission path?
The signal MUST continuously follow the original waveform throughout the transmission from input to output.
Can that ever be applied to any form of chopped signal representaion of an analogue signal?
No!
At least not as far as my imagination or current knowledge will allow me to follow.
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Old 15th September 2009, 01:09 PM   #28
Eva is offline Eva  Spain
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A class D modulator translates amplitude into time.
PWM translates back time into amplitude. Resolution in the time domain is infinite (or limited by quantum physics). Resolution in the amplitude domain is limited by noise floor, and is actually worse than time resolution. Only digital modulators using quantized time may have a limited resolution, but analog modulators doesn't.

What is limited in translations between time and amplitude domains is frequency response. Above half the sampling frequency, components are mirrored back to below Fs/2.

Amplification using the time domain has its advantages, amplitudes get distorted easily (harmonics), time information doesn't (jitter).
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Old 15th September 2009, 01:27 PM   #29
Pafi is offline Pafi  Hungary
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AndrewT!

Simply telling that the other one is wrong shows no intelligence at all. Try to make any argument! And answer the question! You can say as small (positive) value as you wish, the PWM signal will be able to represent.

Quote:
The signal MUST continuously follow the original waveform
Continuity has two aspects: continuity in time, and continuity in value set! A signal can be fully discrete (sampled and digitized, Pulse Code Modulation), or discrete in time, but continuous in value set (sampled analog signal, Pulse Amplitude Modulation), or continuous in both domain (simple analog), or discrete in value sets, but continuous in time (quantized=stair signal).

If input signal is bandwidth limited, then you don't have to transmitt every time-points, you can recover the original signal from discrete samples (shannon's theorem). The sampled signal has the full information, and it is analog (despite the fact that it doesn't follow the original signal)! If these samples are not represented by amplitude of the pulses, but by the width of the pulses, the information remains exactly the same, so it is obviously still analog. (However it cannot be recovered perfectly by simple filtering.)
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Old 15th September 2009, 03:15 PM   #30
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Any jittery digital signal can be considered analog. Current flows in portions of charge of a single electrone (or a hole), so any analog signal can be considered digital.
yada yada yada...
Any input on market share?
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