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Class D Switching Power Amplifiers and Power D/A conversion

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Old 12th September 2009, 10:20 AM   #11
Pafi is offline Pafi  Hungary
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Quote:
When will people learn that Class D is analog, not digital?
I hope: never. Class D is neither analog, nor digital. It can be both.
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Old 12th September 2009, 11:51 AM   #12
Bernie7 is offline Bernie7  Singapore
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Quote:
Originally Posted by Pafi View Post
I hope: never. Class D is neither analog, nor digital. It can be both.
...and the reason is?
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Old 12th September 2009, 11:56 AM   #13
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"he original question isn't very specific either"

No, but giben this is a forum for home audio, i take it he means . in the market for home audio

Just one brand, but a mid-fi mass market one, but i believe several or all Rotel amps are now Class D
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Old 12th September 2009, 12:31 PM   #14
AndrewT is offline AndrewT  Scotland
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ClassD is a switching amplifier that can use Pulse Modulation to create sort of squarewaves that have an average power roughly equivalent to the analogue voltage we had in the input signal.

That switched signal is very similar to the 0s and 1s that are binary. Thus we have the confusion that the ClassD is digital.

Analogue it certainly is not.
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Old 12th September 2009, 11:50 PM   #15
wwenze is offline wwenze  Singapore
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Signals entering Class-D amp pass through a comparator, that is what generates the square wave.

So, is the output of a comparator analogue or digital?
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Old 13th September 2009, 04:10 AM   #16
dweekie is offline dweekie  United States
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Originally Posted by AndrewT View Post
That switched signal is very similar to the 0s and 1s that are binary. Thus we have the confusion that the ClassD is digital.
I thought the main source of confusion was the fact that people associate class "D" to stand for "Digital" instead of an arbitrary letter.
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Old 13th September 2009, 08:43 AM   #17
Pafi is offline Pafi  Hungary
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If the signal parameter wich carries the information can have any value, then it's analog, if it can have only some certain value, then it's digital. In a Class D amp the information carrier parameter is generally the pulse width. This can be analog or quantized (digital) too.

For those who has doubts: is FM digital? After the limiter it is square wave too!

Last edited by Pafi; 13th September 2009 at 08:46 AM.
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Old 13th September 2009, 02:42 PM   #18
wwenze is offline wwenze  Singapore
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Signals are just signals... it's only possible to send a waveform, not 0s and 1s. It's how the signal is sampled that matters - if the receiver requires it to have certain voltages for true and certain voltages for false, then it is sampled digitally. Else, analogue. But even so, there can be confusion, for example, is voltage ladder ADC considered digital or analogue, sure it is an A-D converter, but instead of just one and zeros it can have values of 2 to 15.

So to answer the above question, FM is a sine-ish wave clipped to look square after the limiter, but it is sampled as analogue.

Well, you can even ask if the square wave played through the speakers is analogue or digital.

Last edited by wwenze; 13th September 2009 at 02:46 PM.
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Old 13th September 2009, 04:08 PM   #19
Bernie7 is offline Bernie7  Singapore
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Isn't digital defined by info that's carried in binary coded (not incidental) state, and once it ceases to be in that state, it's analog (whatever it is, it's certainly not digital).

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?

Square waves, saw-tooth waves, various carrier waves and their modulation schemes (FM. AM or PWM) are irrelevant. Leave aside the issue of what's possible - anything is possible in time, one day we may sprout wings too! If PWM today handles and processes the signal in the coded binary state, I might accept that Class D amps are digital too.

Last edited by Bernie7; 13th September 2009 at 04:28 PM.
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Old 13th September 2009, 06:57 PM   #20
Pafi is offline Pafi  Hungary
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Bernie7!

Quote:
If PWM today handles and processes the signal in the coded binary state, I might accept that Class D amps are digital too.
2 examples:
- All (or almost all) ClassD amps of TI processes digital signal until the last (power) stage.
- PIC's and others microcontrollers have in-built PWM modulator wich is definitely digital.

This doesn't mean Class D is digital. Class doesn't tell anything about this.

Quote:
Isn't digital defined by info that's carried in binary coded (not incidental) state,
Don't confuse digital and binary! Digital=the way you count on your fingers. (Natural numbers.) Digitus(lat)=finger. Binary=one digit is from a set with two members.

wwenze!

Quote:
It's how the signal is sampled that matters
What if it is not sampled at all?

Your definition is unusable, and seems to be contradictional to the usual one.

"A digital system is a data technology that uses discrete (discontinuous) values. By contrast, non-digital (or analog) systems use a continuous range of values to represent information." Thats all. No sampling need to be mentioned.

Quote:
FM is a sine-ish wave clipped to look square after the limiter, but it is sampled as analogue.
What sampling do you refer to, and why do you say it's analog?

Quote:
is voltage ladder ADC considered digital or analogue, sure it is an A-D converter, but instead of just one and zeros it can have values of 2 to 15.
I absolutely don't understand this. How could you ask if ADC is analog or digital? It's mixed! 2 to 15 ?!? What are you talking about?
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