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Old 12th April 2011, 12:44 AM   #1601
davada is offline davada  Canada
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Quote:
Originally Posted by Bob Cordell View Post
Hi David,

I'm guessing that is what the manufacturers are doing, but without much success. Maybe they just need better algorithms. Even if they did not do modeling measurements and just extracted the data from the curves in their datasheets, and could create model parameters that would reasonably match the datasheet info, that would be nice.

Cheers,
Bob
I was thinking along the lines of a DIY project for this. But this would be an enormous undertaking for one person. What about a collective effort kind of like how Linux is handled.
One coordinator and many techs undertaking smaller parts of it. Each contributing there expertise.

David.
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Old 13th April 2011, 11:37 AM   #1602
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Default Figure 11.17 MOSFET Amplifier Simulation

Quote:
Originally Posted by rolandong View Post
Hi Bob,

Thanks for writing your book.
I simply can't find book with good grasp on mosfets.

Could you pls. kindly upload LTSpice simulation file for high performance mosfet amplifier from chapter 11 fig.11.17?

thanks in advance,
roland
Hi roland,

As you requested, attached below is the simulation folder for the MOSFET power amplifier shown in Figure 11.17 of my book. The amplifier includes two output pairs each biased at 200 mA, and employs TMC input compensation. It simulates at THD-20 = 0.0014% at its max power output of 44V peak into 8 ohms. THD-20 decreases monotonically as output power is decreased. EKV models are used for the output MOSFETs.

Cheers,
Bob
Attached Files
File Type: zip Figure 11_17.zip (13.7 KB, 98 views)
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Old 13th April 2011, 12:08 PM   #1603
PHEONIX is offline PHEONIX  Australia
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Quote:
Originally Posted by Bob Cordell View Post
Hi roland,

As you requested, attached below is the simulation folder for the MOSFET power amplifier shown in Figure 11.17 of my book. The amplifier includes two output pairs each biased at 200 mA, and employs TMC input compensation. It simulates at THD-20 = 0.0014% at its max power output of 44V peak into 8 ohms. THD-20 decreases monotonically as output power is decreased. EKV models are used for the output MOSFETs.

Cheers,
Bob
Hello Bob,

Out of curiosity how close to the simulated results are the actual real measurments of this amplifier, I am assuming you have built this amp.

Regards
Arthur
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Old 14th April 2011, 12:41 AM   #1604
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Thanks Bob!
I'll surely take a look in next weeks holiday.
Looking forward to build your amp.
I find it good balance between complexity and efficiency (good sound of coarse)

Thanks a lot!
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Old 14th April 2011, 08:48 AM   #1605
Macleod is offline Macleod  France
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Hello Bob,

The world is small as I wanted to ask today the same question as Roland. You gave me some answer right now by providing the simulation files. I will investigate more with them following days.

Thank you for this.

Moreover, I would like to ask you something I can't find in your book up to now.

Fig9.7 gives the basics of the compensation used for your design. MIC (Miller Input Compensation) is used and several R-C networks added on the high impedance points. Your Mosfet Amplifier Fig11.17 also has TMC (Transitionnal Miller Compensation). Your Mosefet Amplifier Fig25.15 also has MIC.

My question is : What is your methodologie to make all that work stable with good phase and gain margin? There are 7-8 components to tune, we are far from the simple Miller compensation used in more common amplifiers.

Do you probe the various loops (which one?) and adjust phase and gain margin for each one? How do you balance the value for each R-C couple? Do you step all components up to a good result? How do you define the work is finished?

I would be interested if you could share the way you work before providing the final results.

If other talented designers could also share the way they would adjust such a design, I would appreciate it very much!

Thank you all for your comments!

Regards

Laurent
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Old 14th April 2011, 08:58 AM   #1606
Macleod is offline Macleod  France
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... plus C24/R21 in your last simulation file...

Last edited by Macleod; 14th April 2011 at 09:00 AM.
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Old 14th April 2011, 03:09 PM   #1607
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Quote:
Originally Posted by PHEONIX View Post
Hello Bob,

Out of curiosity how close to the simulated results are the actual real measurments of this amplifier, I am assuming you have built this amp.

Regards
Arthur
Hi Arthur,

Actually I did not build this amplifier. As you know, SPICE simulations, especially of power amplifiers, can be optimistic or even under some conditions in certain regards pessimistic.

An example of SPICE being optimistic would be if the transistor models are more ideal than in reality. An example would be real-world Early effect being more significant and nonlinear than as modeled. Another example of SPICE being optimistic would be the absence of real world impairments, such as the use of ideal power supplies in the simulation, perfect grounding in the simulation, and absence of nonlinear magnetic field coupling from the class AB output stage in the simulation.

An example of one aspect of SPICE possibly being pessimistic as compared to the real world might be the SPICE FFT showing higher-order THD components in a MOSFET amplifier, possibly due to shortcomings in the square-law or EKV model, or shortcomings in the simulation or FFT of the results.

Cheers,
Bob
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Old 14th April 2011, 04:23 PM   #1608
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I have not yet figured the trick for getting the high order junk to go away.
Stuff that can be nothing else but the mathematically mutilated leftovers
of too many in"significant" digits...

Your FFT is nice and smooth, mine always look like sandpaper. What gives?
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Old 14th April 2011, 07:34 PM   #1609
jcx is online now jcx  United States
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I still get baseline hair but Blackman window puts it a little lower, more points in the sim is good - the maximum timestep in the .tran sould give several times as many sim points as the fft points so the interpolation filter input exceeds Nyquist, then the smoothing filter length can be increased
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Old 14th April 2011, 10:06 PM   #1610
PHEONIX is offline PHEONIX  Australia
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Default Simulation of THD and reality

Hello Bob

Thankyou very much for your response. In my experience I think that its not trivial to get THD-20 =0.001% at 44V peak into 8R (200K BW) and going to 0.0001%(1ppm) is very hard in real hardware. Curiously the simulator is OK at predicting say the Blamless circuit performance but begins to get very optimistic at the 0.0001% levels I think that to get real circuit performance at these levels your simulated THD needs to be much lower.

Regards
Arthur
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