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Old 9th August 2012, 10:52 AM   #71
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by dirkwright View Post
. This means, that for these kinds of I/V circuits (like the Zen/Cen/Sen also), you need two of them plus a following circuit that has a high CMRR, since none of these circuits has any CMRR capability. For stereo, you need four of them. If someone just uses the Iout+ pin only, for example, the distortion will be much higher than that quoted by the manufacturer. So, this is a tough problem.
This topology is very flexible.
below is one solution for this "tough problem".
It has CMRR capability and PSRR ( all the connections to power supplies are made by current sources) and low noise, low distortion.

We make a very good team.
You are good in finding problems...
and i like to find solutions.

Just kidding , i find very challenging your observations, and i thank you for that.
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Old 9th August 2012, 11:29 AM   #72
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by Joachim Gerhard View Post
There are also some very ineresting SMD Zetex with high and linear Hfe and low Rbee`.
More tomorrow.
Yes i know.
NXP also has the BISS bipolar family.
low Rbee is also important for the output transistors.
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Old 9th August 2012, 12:03 PM   #73
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To use a mirror in the second stage or a folded cascode is a bit a matter of taste.
In post 70 we even see a mix of a mirror and a cascode.
What i found most interesting from the beginning is the returning of the base current. One of the major problems of BJt circuits.
In the Sampler mirror the idea is not that different but the solution. The Sampler mirror looses two base currents and adds them on the output so this is feed forward.
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Old 9th August 2012, 12:19 PM   #74
Shinja is offline Shinja  Japan
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would wilson current mirror be the solution?
the schematic i uploaded was mere a concept.

Last edited by Shinja; 9th August 2012 at 12:22 PM.
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Old 9th August 2012, 01:09 PM   #75
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by Shinja View Post
how about this mod to merge differential current from dac.
I made current source Q9 and Q10 works as current mirror.
I3 is for Icq of Q3 and Q6.

this configuration looks similar to
http://home.tiscali.nl/data.odyssey/Super_TIS.html
Hi Shinja,

your concept seems interesting, i will simulate that.
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Old 9th August 2012, 01:25 PM   #76
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by MiiB View Post
This circuit has potential.... very nice concept. with good housekeeping, it has potential to be a great performer.
Thanks MiiB. feel free to contribute, there's a lot of work to be done.
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Old 9th August 2012, 02:42 PM   #77
MiiB is offline MiiB  Denmark
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I'll watch this, and when the concept is a little more settled, I'll start simulating and add servo-ed housekeeping, but first we must decide the front end and how to get the signal out from there...for me the optimum would be to use cascodede current mirrors to currrent assemble the signal. This gives us the option of adding a filter, We could then buffer using Joarcims N-Fet buffer and servo through the housekeeping, this has proven to be a s strong solution in the paradise, Cant see why it should not be a very good solution here as well...

a question is how to handle the offset center current

Last edited by MiiB; 9th August 2012 at 02:45 PM.
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Old 9th August 2012, 05:10 PM   #78
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Quote:
Originally Posted by smms73 View Post
This topology is very flexible.
below is one solution for this "tough problem".
It has CMRR capability and PSRR ( all the connections to power supplies are made by current sources) and low noise, low distortion.

We make a very good team.
You are good in finding problems...
and i like to find solutions.

Just kidding , i find very challenging your observations, and i thank you for that.
Thanks. That's an interesting idea you posted.
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Old 9th August 2012, 05:21 PM   #79
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Quote:
Originally Posted by smms73 View Post

the classic current to voltage converter build with the opamp don't have cmrr capability either, it also need a differential to single end converter. Or you can use balanced connections to the power amplifier.

Relax


Right, the typical following balanced to single ended opamp in the circuit shown in the DAC data sheet has the CMRR to reduce distortion. The bad thing about these classic circuits is that the first stage inverting opamp will contribute some distortion from the common mode signal which will not be canceled by the following opamp. I feel that it would be ideal to have a first stage connected to both the Iout+ and Iout- pins with a high CMRR. So, your proposal would be terrific if it does have a high CMRR also. I'm not talented enough to come up with a good circuit like this.
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Old 9th August 2012, 05:26 PM   #80
MiiB is offline MiiB  Denmark
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Normally a CCS current drive has extremely high PSRR the better the CCS the better the Ratio..CCS also has a great distortion benefit, as the signal than can modulate the working conditions of the circuit, and the DAC currents becomes truly purely additive/subtractive in nature.
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