How many modulation methods in Class D amplifier ? - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 1st November 2006, 12:23 PM   #1
xuhaoz is offline xuhaoz  Sweden
diyAudio Member
 
Join Date: Nov 2006
Default How many modulation methods in Class D amplifier ?

Hi, all,

I am a beginner in this forum, I have read some articles about the modulation method in class D amplifier, and I found that PWM and Sigma-Delta method are the most popular methos used in Class D amplifier.

Do you know any other modulation methods?

What's the relationship between COM and PWM?

Thank you very much.


yours
Jimmy
  Reply With Quote
Old 1st November 2006, 02:57 PM   #2
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
How many do you like ????

Fun aside: Yes the main modulation schemes are indeed PWM and delta-sigma. Both have numerous sub variants however.

COM is a self-oscillating PWM modulator scheme by B&O.

Regards

Charles
  Reply With Quote
Old 1st November 2006, 04:19 PM   #3
diyAudio Member
 
Join Date: Apr 2005
Location: In the Wild, Wild West
Keep in mind there are two sub classes to Class D, Class AD and Class BD. AD means there are only two states for the output, typically the supply rails. BD has three states, usually the supply rails and 0V. Both PWM and delta-sigma can be done in AD or BD. To better describe modulation scheme the type and the sub classe can be used. But then there are lots of other 'things' done that are highly confidential to the companies that create them. All done to improve THD perofromance, reduce EMI, etc. Searching around on the web will pull up lots of info. Just don't be fooled by marketing classes such as Class T and Class I.

-SL
  Reply With Quote
Old 3rd November 2006, 07:48 AM   #4
diyAudio Member
 
Join Date: Oct 2006
Hi,

Yes PWM and Delta Sigma. PWM is good for helping out with THD. The reason being that since the driver stage will have a rise a fall time that is not 0 so when trying to make a certain output level, say half-scale you will be driving the output stage with a 50% duty cycle but there will be a little bit extra due to the rise and fall time. Since in PWM the switching frequency is fixed, this extra amount is the same no matter what output level you are trying to create. To instead of making THD, it simple make a slight DC offset. If you were to use Delta Sigma, (meanign the output switching frequncy varies with output amplitude) the artifact of rise and fall times will cause THD. Think of it like this.
In Delta Sigma, when triyng to make a 1/2 ful scale output, the output switching frequency might be say 800kHz. However when going to 3/4 full-scale, the frequency is now only 600kHz. Since everytime yo switch, you add an extra error caused by the rise and fall time, the error you add is actaully dependent on the output amplutide you try to generate. This will cause THD.


Sorry if I bore you with some of the limited theory I know, but I thought you might be interested.


Dustin
  Reply With Quote
Old 3rd November 2006, 10:40 AM   #5
xuhaoz is offline xuhaoz  Sweden
diyAudio Member
 
Join Date: Nov 2006
Hi, I really appreciate for your explaination.

BTW, if I use PWM topologies, which method do you recommend to implement on a chip ? half bridge? full bridge ? or self-oscillating(hysteresis , phase-shift controlled) ?

Also , please recommend some articles and threads , thank you very much.

Jimmy
  Reply With Quote
Old 3rd November 2006, 02:37 PM   #6
fredos is offline fredos  Canada
diyAudio Member
 
Join Date: Mar 2005
Location: Quebec
You can make lot of variant. What I use is fixed PWM at 500Khz a low level and with a PLL slow down to 250Khz a hight power. This help a lot to reduce THD a low level and increase effiency at hight level, when THD is (a bit) less important. Just remember to do first switching frequency step of at least 20Khz to avoid beating between channel if you use common supply! That some kind of delta-sigma modulation without disadvantage! The more hard with this technique is to design feedback that will remain stable...Easy to do do if you think a lot about this! That what I use in my HVI amplifier..

Fredos
www.d-amp.com
  Reply With Quote
Old 3rd November 2006, 03:26 PM   #7
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Some Self-oscillating toploogies behave like that without further effort !

Regards

Charles
  Reply With Quote
Old 3rd November 2006, 04:21 PM   #8
diyAudio Member
 
Join Date: Oct 2006
Hi,

I dont have any experience with "self ocsillating designs" but I have designed a few different digital modultors. One that I did was for doing a headphone amp, and I have also designed modulators that are for high power (100W RMS or so) but really, the modulator is the same, just the ouptut stage can be scaled up for more power. The prototpyes I have designed have been able to reach 106dB of DNR . (That is take a -60dB input signal and notch it out, then measure all the rest of the noise in the 20-20kHz bandwidth and A-weight). I have found that TI has come out with a digital modulator that goes to a bit better than this, so I bought their refference design and will measure it. The modulators I have used are Sigma-Delta (a 9th order one) and PWM. I am really interested in learning the other meathods people use because I think it just plain cool.

CLD.
  Reply With Quote
Old 3rd November 2006, 04:25 PM   #9
Pafi is offline Pafi  Hungary
diyAudio Member
 
Join Date: May 2004
Location: Budapest
Quote:
this extra amount is the same no matter what output level you are trying to create. To instead of making THD, it simple make a slight DC offset.
This is not true. Timing error caused by fall and rise time depends on output current in a nonlinear way, no matter PWM or sigma/delta.
  Reply With Quote
Old 3rd November 2006, 08:18 PM   #10
diyAudio Member
 
Join Date: Oct 2006
Hi Pafi,


Well im sold on that, I will take back that statement.


Thanks for catching me on that,


CLD
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
AD Vs BD Modulation in Class-D Workhorse Class D 87 27th October 2012 06:33 AM
Class d control methods: UcD / LF analogspiceman Class D 49 3rd April 2005 12:44 PM
Alternative modulation schemes for class d amps Nirav Desai Class D 6 10th January 2005 09:26 AM
Class D Modulation Scheme pokka Class D 7 15th December 2004 07:33 PM
new class D modulation method? sfx Class D 12 6th October 2004 07:02 AM


New To Site? Need Help?

All times are GMT. The time now is 11:50 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2