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Old 12th June 2004, 06:04 PM   #1
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Default V/I Converter

I have seen the threads on the I/V converter but that is not what i need !

1st off all, when is a circuit an V/I Converter ?
When it has a sufficient low output resistance and is able to deliver enough current (class-A) ?

Using Current is a nice way to transport information over.
And since i am thinking of a modular pre-amp (multiple preamp boards on a motherboard like accuphase is doing) i am thinking of their idea on V/I conversion !


Any one suggestions / idea's ?

grtz

Simon
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Old 12th June 2004, 09:40 PM   #2
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What you are looking for is called a "transconductance amplifier". Do a web search and you will find plenty of them. One example is the (discontinued) Burr-Brown OPA622.
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Old 13th June 2004, 08:47 AM   #3
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Thanks,

i thought of that my self as well !


grtz

Simon
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Old 13th June 2004, 09:17 AM   #4
boholm is offline boholm  Denmark
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If you are thinking about building it yourself using transistors and not op-amps, then you could look at those pre-amplifier DIY projects, you can find on the net, and then take away everything after the VAS-stage, including the bias-regulating circuit. The VAS-stage normally gives out current. But then you need to look at the other end: The input stage of the "reciever". You will have to match the output current with the impedance of the input stage.
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Old 13th June 2004, 09:59 AM   #5
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Default Re: V/I Converter

Quote:
Originally posted by blu_line
[snip]1st off all, when is a circuit an V/I Converter ?
When it has a sufficient low output resistance and is able to deliver enough current (class-A) ?
[snip]

Hi Simon,

The output impedance of a V/I converter is ideally infinite. That means, it will deliver an output current controlled by the input voltage. The output voltage then depends on the load. V/I converters are a nice way to control a stage gain without feedback.
BTW, you may think that if you load a V/I stage by an infinite load, that would give infinite output voltage and thus infinite gain! Not so, because the max output voltage depends also on the supply voltage of the circuit, of course. Normally the max voltage that the output can give, while still maintaining the output current is called the compliance. MAX435/436 are examples of V/I converters.

Jan Didden
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Old 13th June 2004, 12:52 PM   #6
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Quote:
MAX435/436 are examples of V/I converters
Checked those out !

What kind of performance could be expected when build up by discretes ?

Got something in my LT Spice but that isn't promissing !
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Old 13th June 2004, 01:27 PM   #7
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S-T,

What you need are a couple of THAT340's or others of the family, from www.profusionplc.com (BTW, I'm going to order a couple, you want to join?).

Jan Didden
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Old 13th June 2004, 06:36 PM   #8
Steven is offline Steven  Netherlands
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Hi Simon,

Any differential pair is actually a voltage to balanced current converter. The only problem is that the input voltage range is very limited without emitter or source degeneration. The link gives an overview of several techniques to increase the input voltage range and the linearity of voltage to current converters.
http://www.eecg.toronto.edu/~kphang/ece1371/mixers.pdf

Steven
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Old 14th June 2004, 07:09 AM   #9
hjelm is offline hjelm  Sweden
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Thanks Steven,
Very informative document.
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Old 14th June 2004, 03:40 PM   #10
thanh is offline thanh  Viet Nam
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I must say that steven know much good document!
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