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-   -   Direct PDM input to GaN E-mode HEMT Class-D Amplifier (https://www.diyaudio.com/forums/class-d/323714-direct-pdm-input-gan-mode-hemt-class-amplifier.html)

Bunpei 10th June 2018 01:50 PM

Direct PDM input to GaN E-mode HEMT Class-D Amplifier
 
1 Attachment(s)
GaN Systems is providing an evaluation board for applying GaN E-mode HEMT as a switching device to a class-D audio amplifier.
GS61004B | GaN Systems
https://gansystems.com/wp-content/up...Rev-171017.pdf
The board assumes a PWM input signal of sampling frequency up to 400 kHz.
Bunpei thought, not only PWM but also PDM, namely delta-sigma modulated 1 bit signal (DSD) might be feasible because a gate driver device, PE29102 is capable up to 40 MHz and GaN E-mode HEMT GS61004B is capable up to 100 MHz.
He told his idea to Professor Yamasaki of Waseda University, who is a leader of 1 bit audio community in Japan. The professor immediately purchased the evaluation board and got a preliminary successful result with TASCAM DA-3000 as a 1 bit signal generator and YAMAHA NS-10M studio monitor as a speaker for 2.8 MHz delta-sigma modulated audio source.
Bunpei got his board today and succeeded in playing 2.8, 5.6, 11.3 MHz sources by using SDTrans384 designed by Chiaki Nakajima as a transport. In his case, not a speaker but a earphone, Etymoic Research ER-4S was used.
Bunpei speculates the experiment by Professor Yamasaki is the first achievement of class-D audio amplifier with direct PDM input.

CFT 10th June 2018 05:32 PM

Revolutionary!
Hows the sound quality? :)

rickmcinnis 10th June 2018 07:02 PM

This is going to be interesting.

Bunpei 10th June 2018 11:33 PM

Hi, CDT!

Thank you very much for your immediate reply!

As for its SQ, I hesitate to show my comment so far because I am listening just a single channel and using commodity level DC power supplies. No modifications are applied to the board. However, it has a good nature worth doing further tunings.

Bunpei

JohnnyInBris 11th June 2018 05:46 AM

There are a number of issues that need to be considered when converting a PDM signal to analog with a power module like this:

Power Supply - an extremely well regulated and decoupled power supply is required to suppress modulation of the supply voltage(s) by the signal that will cause amplitude related distortion

Inter Symbol Interference - unequal rise and fall times or dead times causes the magnitude value of say the positive symbol to not equal that of the negative symbol

Output Filter - complexity will increase as the parasitic elements of the inductor and capacitor in the typical class-D filter will become more significant at higher frequencies

Feedback - cannot be applied to correct any distortions introduced by the above

Switching Losses - will be significantly higher than for class-D thus limiting the available power

Tibouchina 11th June 2018 06:10 AM

A competitive idea?
 
Quote:

Originally Posted by Bunpei (https://www.diyaudio.com/forums/class-d/323714-direct-pdm-input-gan-mode-hemt-class-amplifier-post5458236.html#post5458236)
Bunpei speculates the experiment by Professor Yamasaki is the first achievement of class-D audio amplifier with direct PDM input.

There are commercial products available which do similar things conceptually. The maxim chip handle stereo PDM and requires no output filter.
See: https://datasheets.maximintegrated.c...s/MAX98356.pdf.

Bunpei 11th June 2018 10:19 AM

To JohnnyInBris
Yes, you are completely right. We may expect a lot of challenges. Among them, the most difficult one must be a power supply as you listed it at the top.
Therefore, I think our goal should not be the high-end audio.

To Tibouchina
Oh, we have not known the MAXIM chip at all. Thank you very much for letting us know it!
When we look at its input and output, it has the same spec as the one we reported in this thread. There might be a different mechanism inside the chip because the diagram of the chip shows a “DAC”.

Bunpei 15th June 2018 03:49 PM

1 Attachment(s)
I tried a stereo configuration by using two evaluation boards.
No problems were found.
Direct play of DSD sources sounds very naturally.

CFT 15th June 2018 04:21 PM

GaN and HEMTs were novel items in my student time...never thought they could relate to any audio applicatons. :D

Looking forward to your next report on SQ Bunpei san after the power supply side gets optimized too. :)

mterbekke 2nd December 2019 08:02 AM

Quote:

Originally Posted by Bunpei (https://www.diyaudio.com/forums/class-d/323714-direct-pdm-input-gan-mode-hemt-class-amplifier-post5463412.html#post5463412)
I tried a stereo configuration by using two evaluation boards.
No problems were found.
Direct play of DSD sources sounds very naturally.

Thanks Bunpei, certainly a novel.
"Class D" finally gets interesting.

Any updates regarding SQ or feasability for High End audio?


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