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Old 14th June 2004, 03:47 PM   #11
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Hi Simon!

I feel that a fully discrete solution is difficult, if you want
good performance.
If you have issues to get such kingly components from Burr Brown etc.,
then you could try the old LM13600 (NATIONAL and probably lot's of remakes).
Please refer to:
http://www.national.com/pf/LM/LM13600.html
It is a dual transconductance amp, easy to get, low cost.
Performance is OK for "Lo-Fi" and most other analog signal conditioning. If you only need one transconductance amp, then you can parallel both internal amp of the LM13600. This will give you 3db better S/N ratio.

Cheers
Markus
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Old 15th June 2004, 06:58 AM   #12
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yeah, i had a look at the lm13600.
Performance is awful.

I realy need a hi-fi type.
The goal is to see whether audio can better be transported via an normal buffer (Vin/Vout) or transconductance amp (Vin/Iout).

I did some simulations on 2 types of circuits. topology is quite the same , and so are the result (disappointing).
Circuit is realy working perfect, but the 2nd and 3rd harmonic are a disaster.

grtz

Simon
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Old 15th June 2004, 08:52 AM   #13
hjelm is offline hjelm  Sweden
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If it is for current signal transport between devices i have seen a discrete version in a Swedish hifi magazine (High Fidelity) many years ago.
It included a "transmitter" and "receiver" which was in fact a V/I and I/V converter respectively.
Cannot remember if i have the article still, will check but i promise nothing.

In fact if you take the Yadis in the digital thread and terminate the input voltage via a series resistance. Remove the parallel output resistance. Take the output to another yadis input stage with normal configuration you would have a working setup.

This is just to show an example.

What happens if you use a high quality nmos transistor on the output as an emitter follower and a current sink. The other end is terminated in a opamp based IV stage?

If this is not what you are looking for then i am sorry.
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Old 16th June 2004, 05:17 AM   #14
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thanks hjelm.
I'll have a look at your YADIS circuit.


grtz

Simon
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Old 16th June 2004, 08:25 AM   #15
wenye is offline wenye  China
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Hi All,

Aha! It's a interesting work. In the industry applications, current transmittal are very common used in high noise environment. One of the most notable benefit is high noise tolerance thanks to very low(near to zero) input impedance.

In audio applications, as my understand the advantage of current transmittal will be low sensitivity to interconnect cable! If input impedance of receiver is low enough and output impedance of transmitter is high enough, then the impedance of interconnect cable which paralleled on receiver's input port can be ignore (at least in audio band is not too hard to achieve )! In the other words interconnect cable will not effect sonic preformance! So, why we need to pay for high price interconnect cable?! (Now, I thing that guys from high price cable manufactory and agent wanna kill me and reject my thought! ) Isn't it?

I'm now working on a pair of modulars for this thought......
Any suggestion?


Wenyeh
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Old 17th June 2004, 01:03 PM   #16
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I've seen transcoductance amp, current conveyors and etc etc on my search for the VI converter.

The current conveyor is most promissing i think !

Unfortunatly i can not get the bias right. Any one ?
Most worrying to me is what to do with the input where R6 is connected to !

grtz

Simon
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Old 17th June 2004, 08:00 PM   #17
Steven is offline Steven  Netherlands
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Hi Simon-Thijs,

If this current conveyor is your transmitter, then leave out R5 to get a nice current source output with high impedance and good voltage compliancy. R6 is the voltage to current conversion resistor and should be connected to ground (as shown). This will give you a bipolar single-ended voltage input to bipolar single ended current output. With R6 is 1k (as shown) 1V rms in gives you 1mA rms out.

For the receiver you can use the same circuit but use the other input. That means making R3 zero and applying the signal current, coming from the transmitter, to the emitters of Q11 and Q12. Leave out R6. R5 is the conversion resistor from current to voltage. If R5 is 1k, then the output voltage will be 1V rms again.

Steven
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The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973
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Old 18th June 2004, 04:34 AM   #18
wenye is offline wenye  China
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Simon,

Your post was a very common topology of current mode op called CCII. It's a class AB design with high bandwidth and low noise. But, the problem is low CMRR and low PSRR of this kind of circuit. And, it contain potential unstabilization in high frequency in this circuit due to standard wilson-CC emploied.

In the other hand, this CCII circuit contain potential accurate degrade by input stage.

For more infomation you can read many relate article of current mode technoloy...
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Old 18th June 2004, 05:48 AM   #19
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Thanks Steven , i keep being amazed by your knowledge !
Found some nice documents of the CCI and CCII on the net.

I managed to set the DC output voltage to 0 via an intergrator.
To bad. Its equivalent circuit wherein the Q1 and Q2 are switched (see Per Andersons diamond buffer) the DC offset was 0.

Thanks Wenye.
But please explain what you mean with :
Quote:
In the other hand, this CCII circuit contain potential accurate degrade by input stage

Another problems popped up.
Did anyone ever do a FFT of an LT-Spice Sinus Source ?
I hoped they where clean, but they show 2nd and 3rd harmonics.

best regards,

Simon
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Old 18th June 2004, 10:01 AM   #20
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The simulated circuit :
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