Class-D Amplification

Discussion in 'General Electronics Chat' started by lofiboy, May 7, 2012.

  1. lofiboy

    Thread Starter New Member

    Dec 26, 2010
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    Alright so, I mean to begin a discussion over Class-D amps being designated linear or digital. I seem to run into both opinions often, so I want to see your opinions and what the collective knowledge at the forum has to offer as far justification towards either side.

    I would personally put them in the linear category.
     
  2. #12

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    Nov 30, 2010
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    A designer certainly puts them in the digital category because that is the hardest part of the design work. The super high speeds of the switching bring design problems that an audio frequency designer rarely thinks about.

    http://en.wikipedia.org/wiki/Class-D_amplifier
     
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  3. lofiboy

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    Dec 26, 2010
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    While that makes sense from a designer's standpoint, wouldn't you agree that the information is not at all binary?
     
  4. #12

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    It's pulse width modulation so the 1's and the zero's are not the same width (same time of duration). A binary computer would stall if it saw that so, no, it isn't binary, but it still looks digital to me because it is still made of ones and zeros.

    While I'm at it, binary implies groups of 1's and 0's that represent information packets. A class D amplifier does not think about packets (or groups) of 4 or 8 bits that get converted to information. The information is all carried in the width of the pulses. That's another vote for, "not binary".
     
  5. ErnieM

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    "Analog" and "digital" are generally broad categories to describe gross circuit function. Many circuits jump between categories or blend the two.

    Perhaps such amps would best be describe as "digialog." Pronounced dih-ghi-a-log.

    It's a semantic difference anyway. The circuit does what it does no matter what you call it.

    Ultimately, everything is analog anyway.
     
  6. Wendy

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    Mar 24, 2008
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    An article and thread I have on the subject.

    Pulse Width Modulation

    Class D and triangle wave linearity

    PWM is definitely digital , but the front end is analog as part of the conversion process. Any non-linearitys here show up later, so it is important to get it right.

    The point is, it is a conversion process. PWM is also use for many switching regulators (SMPS), though it is often not discussed as such.

    PWM can be stored in binary format. It is done all the time with µC (PICs are a brand). It can be done several different ways and formats, but all of them are binary storage of PWM. I am willing to bet CDs are a form of PWM when it is all said and done.

    Their are two reasons PWM works, it is digital (and the two most efficient states for any device is on or off), and it stores an analog number with a high degree of precision in a digital format. Conversion back to analog is fundamentally built into the process.
     
  7. crutschow

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    But it can be digital without being binary. ;)
     
  8. Ron H

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    I think of digital as encoded discrete information, like numbers or letters.
    As an extreme example of non-discrete PWM, consider a 2-quadrant multiplier, where one of the inputs is PWM, and the other is the voltage that is being modulated. Is the resulting waveform a digital signal? Certainly the switch(es) is on or off, but does that qualify it as digital?
     
  9. crutschow

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    My view is that anything that switches should be classified as digital. Thus PWM is digital.
     
  10. Wendy

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    Agreed, it is 1's and 0's. Encoding is practical, though rarely done.
     
  11. THE_RB

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    Well, could you put the data through "digital logic" like AND OR gates etc?

    To me "analogue" or "linear" refer to electronics where the voltage varies and that is the data.

    If the voltage is in a number of defined states (like in digital logic gates; 0 and 1) and the data is contained in the defined states that is "digital".
     
  12. crutschow

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    OK. So where do you put PWM which has a fixed pulse amplitude but the width varies in an analog fashion (no discrete widths)? :confused:
     
  13. Ron H

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    After filtering (or averaging due to inertia or whatever), it is a D/A converter. Is a D/A converter digital?:p
     
  14. ErnieM

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    So if the voltage doesn't vary in a digital circuit then a one and a zero either have no voltage or they have the same voltage, correct?
     
  15. crutschow

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    I've heard them called "mixed signal" devices.
     
  16. crutschow

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    What do you mean "voltage doesn't vary in a digital circuit"? :confused: A one and a zero always have a different voltage in digital circuits, which is how you differentiate between them, although both may vary in absolute value depending upon the logic family.
     
  17. ErnieM

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    My point exactly.
     
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