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Old 12th October 2013, 10:45 AM   #831
Nikitas is offline Nikitas  Greece
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And which is the output resistor r5 or r6? the whole circuit is inverted so I can only guess, the one at the right.
I still don't get it.
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Old 29th July 2014, 08:44 AM   #832
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Default IVC for PCM1794

I have tried this as an IVC for PCM1794. Very good result. BJTs is optional.
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Old 9th May 2015, 08:50 PM   #833
bcarso is online now bcarso  United States
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Quote:
Originally Posted by smms73 View Post
how do you come to 1k , i think is very low for a current source, if someone knows the real value please post.
My apologies coming in so late, and your question may already have been answered. But in case not:

So-called current-output DACs usually have a code-dependent and often rather low output resistance. They are NOT usually what we would call current sources. A better way to describe them is as having an output which must be connected to a low (even specified sometimes!) impedance input for accurate operation. Of course the standard approach is a voltage-feedback op amp connected as a transimpedance amp. Doing things with bipolars or JFETs as common-base or common-gate inputs is advantageous for a variety of reasons, but without global feedback you have to work pretty hard to have the distortion at the input itself be small and code-independent.

Short of enclosing a common-base or common-gate input design in a global feedback loop, one can also wrap a gain stage around the input devices to reduce the input resistance and equivalent inductance. Such a configuration is adroit at managing the fast rise-fall-time signals out of various DACs.
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Old 9th May 2015, 10:41 PM   #834
CeeVee is offline CeeVee  Portugal
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Quote:
Originally Posted by smms73 View Post
That is a circuit that uses floating power supplies , first I think you should check this thread to grasp the concept, then if you still need I will explain the rest. Dont forget that the current that is injected to the circuit by the I1 will have to return to ground and the only path is by the output resistor.

Zen -> Cen -> Sen, evolution of a minimalistic IV Converter
Sergio,

You are obviously a talent ...give us your vision otf the practical aplication.

I know you are still in Academia but this is about the music ....i want to hear your ideas....implemented.
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Old 10th May 2015, 02:57 AM   #835
bcarso is online now bcarso  United States
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Quote:
Originally Posted by smms73 View Post
thanks jcx .That is also my experience. I will talk more about this later, as I think is very important.
One closer approximation in simulation and reality is to have some finite source impedance. This is particularly critical when various bootstrapping schemes are deployed.

Often to stabilize and compensate, about all that is required is some lumped C to common for the input. For really high frequencies you may want a little inductance to push resonances lower. I found about 300nH enough for a group of three paralleled 2SK170 parts (although that was not a bootstrapped drain design---probably of no consequence).
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Old 10th May 2015, 09:58 PM   #836
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by bcarso View Post
My apologies coming in so late, and your question may already have been answered. But in case not:

So-called current-output DACs usually have a code-dependent and often rather low output resistance. They are NOT usually what we would call current sources. A better way to describe them is as having an output which must be connected to a low (even specified sometimes!) impedance input for accurate operation. Of course the standard approach is a voltage-feedback op amp connected as a transimpedance amp. Doing things with bipolars or JFETs as common-base or common-gate inputs is advantageous for a variety of reasons, but without global feedback you have to work pretty hard to have the distortion at the input itself be small and code-independent.

Short of enclosing a common-base or common-gate input design in a global feedback loop, one can also wrap a gain stage around the input devices to reduce the input resistance and equivalent inductance. Such a configuration is adroit at managing the fast rise-fall-time signals out of various DACs.
That is a very old question
I have answer it myself here in post #8 :

Testing the pcm1794

The PCM1794 have a very high output impedance and is very easy to design a very low distortion I/V converter without feedback.
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Old 10th May 2015, 10:07 PM   #837
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by CeeVee View Post
Sergio,

You are obviously a talent ...give us your vision otf the practical aplication.

I know you are still in Academia but this is about the music ....i want to hear your ideas....implemented.
Boas CeeVee,
Thanks,

Sorry, Can you Please specifies what you want, If you prefer send me a PM .
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Old 11th May 2015, 12:33 AM   #838
bcarso is online now bcarso  United States
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Quote:
Originally Posted by smms73 View Post
That is a very old question
I have answer it myself here in post #8 :

Testing the pcm1794

The PCM1794 have a very high output impedance and is very easy to design a very low distortion I/V converter without feedback.
Thanks. Yes, that's the highest I've ever heard of and deserving of being thought of as a current source.
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