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Old 25th November 2012, 09:45 PM   #51
bcarso is offline bcarso  United States
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Quote:
Originally Posted by dadod View Post
Noise
Yep if that 40nV/sqrtHz is output noise, that's quite close to what I roughed out.
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Old 26th November 2012, 03:26 AM   #52
RNMarsh is offline RNMarsh  United States
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Default CMR

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Originally Posted by dadod View Post
Thanks RNM,
when I did it with the input buffer distortion increased slightly, and with the output buffer no change.
Damir
CMR? both ways?
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Old 26th November 2012, 08:09 AM   #53
dadod is offline dadod  Croatia
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Originally Posted by RNMarsh View Post
CMR? both ways?
RNM I have to find out how to simulate CMR, I am quite new in spice simulation.

The main noise contributor is current conveyor input resistor(R28). Changing BC5.. transistors to 2sa970/2sc2244 dropped the noise from 40nV/sqrtHz to 37nV/sqrtHz only.
To have the same gain with lower input resistor I changed CM to equal current in both legs and here is simulation I called low noise low distortion. Additional benefit is lower dissipation of Q6 and Q8 and there are low power transistor good enough now.
If I want to keep that low noise high impedance input volume control is no no. Output resistor(Rout) could be used as an atenuator but 1k only and that is not easy to get by. Any suggestion??
Damir
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File Type: jpg Lownoise-lowdist.jpg (223.9 KB, 259 views)
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Old 26th November 2012, 10:11 AM   #54
dadod is offline dadod  Croatia
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Noise and distortion simulation by changing current conveyor output resistor(R1(Rout)) from 100 to 1000 ohm in ten steps, changing the gain from 0.46 to 4.6.
Damir
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Old 27th November 2012, 08:06 AM   #55
Shinja is offline Shinja  Japan
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you can replace Q3 and Q4 and diodes by complicated buffer as enployed in input and output.

by the way, if you do not intend to use global loop feedback,as CFB opamp,
it may be easy to obtain better performance with folded cascode instead of current mirror.

there are some discussions about similar circuit.
Zen -> Cen -> Sen, evolution of a minimalistic IV Converter
dac I/V convertion with very low distortion
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Old 4th December 2012, 12:26 PM   #56
dadod is offline dadod  Croatia
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There are two examples of the line amps that I think could be good to be built. Both are very close regarding distorstion and noise. Here is the first one. Input 0.3 V and 0.01 V.
Which one to build?
dado
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File Type: jpg THD20k-0.3V-input.jpg (207.3 KB, 198 views)
File Type: jpg THD20k-0.01V-input.jpg (207.6 KB, 183 views)
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Old 4th December 2012, 12:28 PM   #57
dadod is offline dadod  Croatia
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The second one, same input voltage.
dado
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File Type: jpg THD20k-0.3V-input-dbuffer.jpg (199.5 KB, 171 views)
File Type: jpg THD20k-0.01V-input-dbuffer.jpg (206.6 KB, 72 views)
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Old 4th December 2012, 04:43 PM   #58
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Quote:
Originally Posted by dadod View Post
The second one, same input voltage.
dado
Hello ''dadod'',

I would kindly suggest the last SCH from a 4 th published.

Excellent results You achieve there

Congratulations

Best regards

Andreas
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Old 4th December 2012, 07:18 PM   #59
dadod is offline dadod  Croatia
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Originally Posted by Smiley 09 View Post
Hello ''dadod'',

I would kindly suggest the last SCH from a 4 th published.

Excellent results You achieve there

Congratulations

Best regards

Andreas
Thank you Andreas,
There are two schematics only, shown with two different input signals, and you can see all details of the schematics by clicking on the down left corner.
Damir
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Old 4th December 2012, 09:14 PM   #60
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Quote:
Originally Posted by dadod View Post
Thank you Andreas,
There are two schematics only, shown with two different input signals, and you can see all details of the schematics by clicking on the down left corner.
Damir
Hello ''Damir''

Yes I know, and from the two I would gladly chose the second one with absent of 7th harmonic
Well after it'll be built .... yes the PCB design, components influences, and all related other parasitics will take their places would surely be different but for sure this is very, very good starting point and the final proto might even surprise you with the very low distortion sound

Best regards,

Andreas
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