Perhaps noone answered because they aren't familiar with the terms.
Here is a reference for anyone interested ...
http://www.iet.ntnu.no/~ivarlo/files/School/PhD/03_PCM_to_PWM.pdf
-- mirlo
Here is a reference for anyone interested ...
http://www.iet.ntnu.no/~ivarlo/files/School/PhD/03_PCM_to_PWM.pdf
-- mirlo
I remember having seen somewhere some description of commercial design which used 3-level ( BD ) modulation.
When the audio signal was positive, the PWM switched between positive polarity and ALL OFF switches, rather than between positive and negative. With zero input signal, the switches were all in high impedance state, instead of alternately hitting both rails at 50% DC. It seemed to make more sense, also maybe lower DC offset at no signal, but it may be more complex to implement.
I can't recall what manufacturer was providing this info. I'll look through my collection of bookmarks to see if I can find it.
Andy
When the audio signal was positive, the PWM switched between positive polarity and ALL OFF switches, rather than between positive and negative. With zero input signal, the switches were all in high impedance state, instead of alternately hitting both rails at 50% DC. It seemed to make more sense, also maybe lower DC offset at no signal, but it may be more complex to implement.
I can't recall what manufacturer was providing this info. I'll look through my collection of bookmarks to see if I can find it.
Andy
As I have not been aware of the AD Modulation I am surprised about it in several ways.
I am used to the "normal" analog opamp based amps (building headphone amps), so the AD Modulation comes more "natural" to me. Some points that comes to my mind:
You can half the suply Voltage with BD due to the use of the H-bridges. Things like this simply have to come with some drawbacks, the H-bridge adds some extra pice of hardware in the signal path which I would consider as a subotimal,also I could imagine that the zero transits may cause some problems. As mentioned I like Headphones so another bad thing comes in mind, the common ground which is simply impossible with BD design.
As I want to build some active speakers (possibly with additional headphone out) this informations comes in very handy, thanks for this enlightenment.
I would prefer AD design, now that I know of it
, if the dimensioning of the PS is not a big issue.
Then again I'm very much a newbie to audio diy and I may be completely wrong.
I am used to the "normal" analog opamp based amps (building headphone amps), so the AD Modulation comes more "natural" to me. Some points that comes to my mind:
You can half the suply Voltage with BD due to the use of the H-bridges. Things like this simply have to come with some drawbacks, the H-bridge adds some extra pice of hardware in the signal path which I would consider as a subotimal,also I could imagine that the zero transits may cause some problems. As mentioned I like Headphones so another bad thing comes in mind, the common ground which is simply impossible with BD design.
As I want to build some active speakers (possibly with additional headphone out) this informations comes in very handy, thanks for this enlightenment.
I would prefer AD design, now that I know of it
, if the dimensioning of the PS is not a big issue.Then again I'm very much a newbie to audio diy and I may be completely wrong.
No one knows or there's some confusion
It seems that No one knows about my questionarrie....I just asked about Pros/Cons of 2 types of H-Bridge amp in which BD mode has Switching frequency in phase and AD mode has switching Frequency out of phase...thats all.
Hoping this time its little bit more simpler.....
K a n wa r
It seems that No one knows about my questionarrie....I just asked about Pros/Cons of 2 types of H-Bridge amp in which BD mode has Switching frequency in phase and AD mode has switching Frequency out of phase...thats all.
Hoping this time its little bit more simpler.....
K a n wa r
Sorry, Kanvar
I think your topic may be a little over the head of most members, and everyone reading this knows less than you do about it.
You might try asking Eva, by interjecting an off-topic post in one of the SMPS forums she monitors. (Class D is not too different from SMPS).
You might also try emailing tech guys at a semiconductor house like IRF.com, who actively promote class D design these days. Make sure to include a schematic or a mention that you use IR MOSFET part numbers in your design.
(make sure the diodes are IR part nrs also, not MUR...)
They're usually good with replying, and some of those guys feel so passionate about design, once you get them started, you can't stop them.
Andy
I think your topic may be a little over the head of most members, and everyone reading this knows less than you do about it.
You might try asking Eva, by interjecting an off-topic post in one of the SMPS forums she monitors. (Class D is not too different from SMPS).
You might also try emailing tech guys at a semiconductor house like IRF.com, who actively promote class D design these days. Make sure to include a schematic or a mention that you use IR MOSFET part numbers in your design.
(make sure the diodes are IR part nrs also, not MUR...)
They're usually good with replying, and some of those guys feel so passionate about design, once you get them started, you can't stop them.
Andy
This document may helps you:
http://focus.ti.com/lit/an/sloa119a/sloa119a.pdf
As for my understanding BD requires smaller components and has better EMI, having the only drawback of being more dificult to calculate.
Regards,
Ravaz
http://focus.ti.com/lit/an/sloa119a/sloa119a.pdf
As for my understanding BD requires smaller components and has better EMI, having the only drawback of being more dificult to calculate.
Regards,
Ravaz
About EMI and AB/AD modulation:
http://www.hypex.nl/docs/AES124_Masterclass_Putzeys.pdf, pages 81, 82, 83
http://www.hypex.nl/docs/AES124_Masterclass_Putzeys.pdf, pages 81, 82, 83
Who would trade overall EMI performance for eliminating carrier residual only when there is no signal?
Carrier residual applied to speakers is completely harmless. EMI can potentially disturb any piece of electronics around.
Class BD means "wrong design goals". Low EMI should be the first goal.
Carrier residual applied to speakers is completely harmless. EMI can potentially disturb any piece of electronics around.
Class BD means "wrong design goals". Low EMI should be the first goal.
BD modulation
The reason people are interested in BD comes from Delta-Sigma convertors. If you can use a three level output you can decrease quantization noise by 6dB. You also get to utilize the dead time instead of it being your enemy. One problem with BD though is that you lose the inherent linearity of a two level system. The distance between high and low level in a two level is what it is but in a three level the distance (magnitude) from "zero" to high level will be different than from "zero" to low level or negative. This introduces nonlinearity. Otherwise, the BD is kinda neat when you are trying to do a more advanced noise shaped amp, especially if it's a true digital amp.
Cheers
The reason people are interested in BD comes from Delta-Sigma convertors. If you can use a three level output you can decrease quantization noise by 6dB. You also get to utilize the dead time instead of it being your enemy. One problem with BD though is that you lose the inherent linearity of a two level system. The distance between high and low level in a two level is what it is but in a three level the distance (magnitude) from "zero" to high level will be different than from "zero" to low level or negative. This introduces nonlinearity. Otherwise, the BD is kinda neat when you are trying to do a more advanced noise shaped amp, especially if it's a true digital amp.
Cheers
I think Kanwar is talking about what is described in Bruno's paper (which was mentioned some posts before) and not some three-state amp that is using an "open" state.
This has one advantage: The apparent switching frequency and also the actual sampling frequency is twice as high for a given carrier frequency when you use a carrier-based amp. Therefore you can use more loop gain.
Regards
Charles
This has one advantage: The apparent switching frequency and also the actual sampling frequency is twice as high for a given carrier frequency when you use a carrier-based amp. Therefore you can use more loop gain.
Regards
Charles
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.