Class D amplifier
Class D amplifier
A number of years ago, (I don't like to think how many) I designed a switching amplifier for a Sonar transmitter application. Another engineer told me that it would not work because the intermodulation products would be too high. He was right, the sum or difference frequencies were only 6dB below the two tones. So, the question is, how do class D audio amplifiers work? Is the distortion low enough that it is not noticable?
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Re: Class D amplifier
I'm no authority, but I'd put the switching frequency at least one decade higher than the highest frequency I wanted to amplify. The output would then go through a passive low pass filter to reduce the switching artifacts. By having the switching rate that high, you also reduce the aliasing.
Re: Class D amplifier
Texas instruments has a number of devices that are class D for audio use. You can get theory and application info at their site for free.Also try Linfinity.
As for as operation, in the case of the TI amps,the output comes out as a triangle. It is then run through a 2 pole L-C filter to shape the waveform into something more sinusoidal.
I don't know if this information relates well to RF but, it's the best i have.
As for as operation, in the case of the TI amps,the output comes out as a triangle. It is then run through a 2 pole L-C filter to shape the waveform into something more sinusoidal.
I don't know if this information relates well to RF but, it's the best i have.
Re: Class D amplifier
The Texas Instruments class D devices claim low (.01% or better) distortion, but I bet that is with one tone. When there is multiple tones, like music, they are going to mix and produce sum and difference frequencies that are in the audio band and cannot be filtered out. I have not listened to one of these but can't believe it is as good as a linear amp.
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- Posts: 400
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Re: Class D amplifier
Some amplifiers have a multistage scheme with a class D supplying the power to a class AB with just a few volts to spare. The class AB stage cleans the signal. Result? A compromise between class AB quality and class D efficiency.<p>Low THD? Unless stated otherwise, THD is rated at 1kHz. The proof is in the listening. With extremely low THD ratings (assuming they're true), you probably won't notice outside of a sound room. You'll also need speakers that cost more than your car.
Re: Class D amplifier
You can get some information on an interesting Class D design at this site.<p>http://listen.to/audioexperiment
Re: Class D amplifier
Thanks, Joseph, I will explore that site in detail.
Re: Class D amplifier
Your'e welcome, Russ. I have been tinkering with a design similar to the main one on that site.
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