LTspice delay - 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 22nd January 2010, 06:29 PM   #1
Baldin is offline Baldin  Denmark
diyAudio Member
 
Baldin's Avatar
 
Join Date: Jan 2005
Location: Copenhagen
Send a message via MSN to Baldin
Default LTspice delay

A Class-d amp can be described simplified in the time domain as an amplification or gain, a delay of 1 sample freq and the output filter.

How do you model the delay in LTspice??

Have tried to use a transmission line, but it doesent really work ...
What is needed is perfect (same delay at all feq) delay of e.g. 200nS in the time domain.

I want this to be able to model different feedback network in the frequency domain.

Can anyone help????

Thanks in advance and best regards Baldin
__________________
Visit www.sensibleaudio.dk or read latest news on Baldin's Blog
  Reply With Quote
Old 22nd January 2010, 07:30 PM   #2
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
I don't use LTspice, but in the old version of Pspice that I use analog delay lines need a characteristic impedance to be specified, and they need to be driven and loaded exactly from that impedance to avoid problems, for example 100 ohm. Voltage controlled voltage sources may be used for input and output buffering.

I didn't find a better way to do it, as the other type of delay line available in my PSpice is digital and gives a lot of trouble with A/D conversion.
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  Reply With Quote
Old 23rd January 2010, 03:22 PM   #3
Baldin is offline Baldin  Denmark
diyAudio Member
 
Baldin's Avatar
 
Join Date: Jan 2005
Location: Copenhagen
Send a message via MSN to Baldin
Hi Eva

Playing a bit more with the Transmission line in LTspice, and terminating it correctly in both ends, actually seems to work.

I think it was partly not having the right termination and partly not getting what I expected, causing the problems ... I now use 100 ohm in both ends, and 100 ohm line, and added a buffer on the receiving end.

Thanks and best regards Baldin
__________________
Visit www.sensibleaudio.dk or read latest news on Baldin's Blog
  Reply With Quote
Old 24th January 2010, 04:53 PM   #4
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
It should be sufficient to terminate the output side with the same Z that you have specified for the TL. Effective drive impedance should not change the shape, but result in a voltage divider of drive impedance and load.
So far my LT Spice always handled the TL perfectly fine.
  Reply With Quote
Old 24th January 2010, 04:58 PM   #5
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Add on:
The drive impedance should not change the shape as long as the drive impedance is not complex. With complex drive impedances you will get a frequency depending divider, which will result in changed shapes.
  Reply With Quote
Old 24th January 2010, 05:02 PM   #6
Baldin is offline Baldin  Denmark
diyAudio Member
 
Baldin's Avatar
 
Join Date: Jan 2005
Location: Copenhagen
Send a message via MSN to Baldin
Hi ChocoHolic

Well, that was also my fault ... I did not load it at the output with the same impedance as specified for the line .....
On the other hand, it overall didn't look as expected ...... so I thought it was only because the modeling was wrong .... some was, some was my thinking

As the moment I'm strugleing with my design stopping to oscillate when not loaded (real life test, not simulated) ... funny thing is I have one oscillator board with a MXL1016 that work without problem, but the LT1711 board stops whan the load is removed ... and will not start without load either (and mosfets heat up ) .... ... one difference is of cource the output being 0/5V on the MXL, and +-5V on the LT ..... but going through the rest of the amp this shouldn't matter!!
__________________
Visit www.sensibleaudio.dk or read latest news on Baldin's Blog
  Reply With Quote
Old 24th January 2010, 05:42 PM   #7
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Hi Baldin,
is the Pin5 of the 1711 properly connected to -5V?
  Reply With Quote
Old 24th January 2010, 05:52 PM   #8
Baldin is offline Baldin  Denmark
diyAudio Member
 
Baldin's Avatar
 
Join Date: Jan 2005
Location: Copenhagen
Send a message via MSN to Baldin
Quote:
Originally Posted by ChocoHolic View Post
Hi Baldin,
is the Pin5 of the 1711 properly connected to -5V?
Yes
(but you can actually keep it floating also ... but it is connected to -5V in the design)
__________________
Visit www.sensibleaudio.dk or read latest news on Baldin's Blog
  Reply With Quote
Old 24th January 2010, 06:00 PM   #9
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
...too bad. Pin5 would have been such a simple solution...
Anyway, good luck!

P.S:
You have a nice home page! ...and a seperate room for the home theatre!!! *envy*
  Reply With Quote
Old 24th January 2010, 06:02 PM   #10
diyAudio Member
 
Join Date: Apr 2006
Location: Minnesota
Use an LTspice BV source. V=delay(V(in),delay_time). It works great; better that using a delay line.
  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
LTSpice tutorial Bonsai Solid State 2 4th February 2011 08:03 AM
Using LTSpice gaetan8888 Solid State 6 19th July 2007 01:33 AM
RIAA in LTspice Herrmann Tubes / Valves 2 17th September 2004 08:28 PM
LTSpice Issue... mikeks Solid State 17 3rd September 2004 08:42 AM
Ltspice.... mikeks Solid State 10 13th June 2004 09:10 PM


New To Site? Need Help?

All times are GMT. The time now is 05:18 AM.


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