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Old 23rd October 2012, 03:13 PM   #21
dadod is offline dadod  Croatia
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Quote:
Originally Posted by AndrewT View Post
what is the difference between loop gain and open loop gain?
What do the .op statements look like for the three conditions you are examining, closed loop gain, loop gain and open loop gain?
Is loop gain the 1/NFB ratio = beta?
Loop Gain(LG) is difference between Open Loop Gain(OLG) and Close Loop Gain(CLG), means OLG-CLG=LG. LG is effective Negative Feed Back at different frequences.
You can't use .op (compute the DC operating point treating capacitance as open circuits and inductance as short circuits) to simulate LG, CLG or OLG, you use .ac for that.
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Old 24th October 2012, 09:22 AM   #22
dadod is offline dadod  Croatia
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No comments or suggestions on PCB layou???
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Old 24th October 2012, 11:20 AM   #23
wahab is offline wahab  Algeria
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No , but about the schematic itself or rather the sims,
how did you compute the gain/phase response.?...
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Old 24th October 2012, 11:35 AM   #24
dadod is offline dadod  Croatia
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Quote:
Originally Posted by wahab View Post
No , but about the schematic itself or rather the sims,
how did you compute the gain/phase response.?...
I hopped for layout comment, as layout discussion in other thread was quite interesting and I tried to follow suggested improvements.
Do you mean LG or CLG?
For LG I do with TMC resistor init and out of Midlebrook probe. Look at attached diagrams.
dado
Attached Images
File Type: jpg LG-TMCin.jpg (229.2 KB, 271 views)
File Type: jpg LG-TMCout.jpg (224.5 KB, 267 views)
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Old 24th October 2012, 01:05 PM   #25
wahab is offline wahab  Algeria
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It was about the CL phase and gain responses.

Anyway to check stability you can use a square signal
and parralel a 10nF to 100nF cap with the load , it is often
quite revealing.
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Old 24th October 2012, 01:31 PM   #26
dadod is offline dadod  Croatia
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Quote:
Originally Posted by wahab View Post
It was about the CL phase and gain responses.

Anyway to check stability you can use a square signal
and parralel a 10nF to 100nF cap with the load , it is often
quite revealing.
I am not sure I understand what you want to know about CLG. How I did the CLG simlation?
I don't have working prototype yet to do Square wave test(I did it on similar standard TMC circuit in my other thread).
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Old 24th October 2012, 02:35 PM   #27
wahab is offline wahab  Algeria
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Your TMC resistor has quite low value and this generaly reduce considerably
the phase margin once the output is capacitively loaded.

As for square wave test i was speaking in simulation , not in real life ,
as the simulator provide a good estimation of an amp behaviour in this matter.
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Old 24th October 2012, 03:29 PM   #28
dadod is offline dadod  Croatia
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OK it is here square 10kHz, no cap, 10n//8R, 100n//8R, 1u//8R and 2.2u//8R
dado
Attached Images
File Type: jpg square-10k.jpg (138.9 KB, 219 views)
File Type: jpg square-10k-10n.jpg (164.5 KB, 206 views)
File Type: jpg square-10k-100n.jpg (164.3 KB, 198 views)
File Type: jpg square-10k-1u.jpg (166.2 KB, 55 views)
File Type: jpg square-10k-2.2u.jpg (159.4 KB, 64 views)
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Old 24th October 2012, 04:39 PM   #29
AndrewT is offline AndrewT  Scotland
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Can you post the actual spice .asc for each of the tests, clg, olg, lg with the appropriate .ac activated so that we can see the differences? and run these if we want to duplicate your results.

If you add a .txt or a add .zip to the xxxxxxxxx.asc file name, the Forum allows these to be attached. Or replace the .asc with either .zip or .txt
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Old 24th October 2012, 05:04 PM   #30
dadod is offline dadod  Croatia
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Here is zip file containig .asc file and models files. Unzip it in the same directory and just run simulation.
There are .tran .ac defined but just one active (.tran or .ac) and others passive(;tran ;ac)
Input generator V4 could be changed from sinus to square just copying the lines already there:
SINE(0 {sqrt(.75)} {freq})
or
PULSE(.5 -.5 0 10ns 10ns .05ms .1ms 8)

there one .ac for (for CLG or LG)
;ac dec 1k 1 1G
and two .tran square and sinus
.tran .4ms
;tran 0 {simtime} {dlytime} {timestep}

dado
Attached Files
File Type: zip Little-GEM.zip (17.3 KB, 44 views)
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