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Class D Switching Power Amplifiers and Power D/A conversion

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Old 29th November 2012, 11:07 AM   #71
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I did some search for dynamic hysteresis control in class-d amps. There are some papers around one for which would have to pay for, for instance from IEEE.

But here are some interesting ones that are freely available:

This one is from ADI and is dealing with delta-sigma converters. From page 84 they explain their implementation of dynamic hysteresis into their range of delta-sigma based class-d amplifiers.


http://www.cscamm.umd.edu/programs/o...dams_ocq05.pdf


This one here is a patent by Toshiba which comes quite close to our proposals. Although the technical implementation is different to our proposals the general idea is quite close. From the legal perspective the claims would have to be analysed in detail in order to be sure. The modulation of the frequency is done via a transconductance amplifier. The patent also shows a way to implement dither to reduce EMI problems. But they don't use post filter NFB. The patent fees are due this year. Maybe they refrain from paying because of lack of interest and the patent will cease.

Espacenet - Bibliographic data

Regards

Charles
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Old 29th November 2012, 11:26 AM   #72
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Default Thanxz for the links Charles...!!!

Here is the better view for the circuit implementation.

Having a transconductance amplifier solves many things in one go. Its complex for DIY but going by results, its equally tempting.
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Old 29th November 2012, 01:09 PM   #74
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I think gain controllable OTAs offer exactly the functionality (2 quadrant multiplier), which help to ease Charles' approach.
LM13600/13700 could be worth a trial.
Critical point would be the bandwidth of 2MHz, which might not reproduce a 400kHz rectangle in a sufficient way way.
Noise of the LM13600 should not be an issue because it would be inside the feedback loop, from my understanding.
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Old 29th November 2012, 01:45 PM   #75
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Something DIY would probably kill an LM13600 performance-wise. Keep in mind that we actually only have to modulate a rectangular signal in Amplitude (no sinusoidal or the like). Therefore it should be possible to turn a positive and a negative current mirror (or some other controllable current-source) on and off.

Regards

Charles

Last edited by phase_accurate; 29th November 2012 at 01:48 PM. Reason: typos
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Old 29th November 2012, 03:14 PM   #76
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Another idea just popped up which is quite simple. The most annoying part of it is the fact that it didn't pop up earlier. I'll post info as soon as I have "tried" it out.

Regards

Charles
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Old 29th November 2012, 03:15 PM   #77
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I wonder if you could use a window comparator, followed by an S-R latch as the modulator instead of a single comparator with hysteresis? I used the same arrangement in the past where I wanted variable hysteresis without all of the tolerance issues that setting an accurate hysteresis level involves. You have to provide symetrical threshold voltages to the window comparator to set the (emulated) hysteresis effect, but that shouldn't be too difficult, although very high speed op-amps would be required to follow the switching waveform. A hastily drawn Visio pic is attached.
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Old 29th November 2012, 03:37 PM   #78
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Very nice and even simpler than the idea that I just had. And even more embarassing for me .....
My new idea was a mixture of the one that I presented and Markus' clamping idea. Now I wonder if it still makes sense to present it.

BTW: No need for very high speed OP-AMPs because they would not have to handle the switching signal. They are used to generate the hysteresis level as a function of the audio signal. They would not even have to offer low THD or low noise.

Regards

Charles

Last edited by phase_accurate; 29th November 2012 at 03:40 PM.
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Old 29th November 2012, 05:36 PM   #79
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...absolutely great. I love your contributions!

Regarding the build itself I am tending to the simple solution of posting #3,
because it seems to serve the needs (==> low HF ripple and 15db improved THD at 90%) and at the same time makes Mr. Nitpicker happy:
18 components
40 solder joints

But besides this 'low brainer comment' let's go on with the discussion
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Old 29th November 2012, 06:12 PM   #80
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Quote:
Originally Posted by phase_accurate View Post
Another idea just popped up which is quite simple. The most annoying part of it is the fact that it didn't pop up earlier. I'll post info as soon as I have "tried" it out.

Regards

Charles
An option for Mr. Nitpicker?
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