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12th January 2013, 01:57 PM  #31 
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Yes, but notice that the very small value carbon resistor is used to minimize the lead inductance of a large tantalum capacitor, not the smaller 0.1uF bypass capacitor. This technique appears to only be useful when using relatively large bypass capacitors and only if you use a carbon resistor, or some other type that has very low inductance at radio frequencies.
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12th January 2013, 02:05 PM  #32 
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If the inductance contributed by the resistor concerns you then select a smaller package size  0603 perhaps or 0402 if your eyesight is good enough. Its the total loop inductance that's important, not just that of the resistor  so if the resistor adds to the loop area it will increase the inductance. OTOH if the resistor's just replacing a wire that would be there anyway, it won't add inductance. This is assuming normal thick film SMT resistors of course, not wirewound ones.
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12th January 2013, 02:16 PM  #33  
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Quote:
I assumed that the datasheet portion under discussion applied to through hole devices (since the AD797 is available that way) which have more lead inductance than SMD's. The datasheet specifies a carbon resistor.
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12th January 2013, 02:28 PM  #34  
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Quote:
The use of snubbers is less important for decoupling purely analog circuits that aren't handling fast rise time signals and hence aren't taking big, fast gulps of current like CMOS digital chips do. I do recommend them for such applications, on pure analog handling audio band signals its a tossup whether there's any benefit.
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12th January 2013, 02:38 PM  #35  
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Obviously, digital circuits have different power supply requirements than analog ones, and it's debatable whether or not an opamp in an IV converter for a DAC sees enough digital surges to warrant this kind of snubber circuit. I would like to see some hard data on that before bothering with it. Do you have any?
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12th January 2013, 02:47 PM  #36  
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Quote:
Quote:
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12th January 2013, 02:56 PM  #37 
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I may be forced to use SMD's in the near future, so I have some interest in this idea. The LME49990 is particularly difficult to implement, according to their data sheet (and comments by others), for example, and this technique may be useful for that part. I'd be interested if you know of someone who has made this comparison if you don't have it. I assume that Analog Devices didn't invent this idea out of thin air but instead came up with it to address a specific problem they were having with the AD797. I understand the theory of course, but would like to see data on how much of a difference it makes. I can try to do a Google search myself but I am not hopeful about finding something useful.
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12th January 2013, 03:02 PM  #38 
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Power supply decoupling would be the least of your worries if you're considering either of those opamps in close proximity to anything digital as I understand they don't coexist very happily with RF. Walt Jung (who works for ADI) even designed out the AD797 in his regulator as it misbehaved when powering digital stuff.
<edit> Here's a paper which anyone considering an opamp with input LTP for I/V would do well to read and digest : http://www.uemc.polito.it/papers/opampsusc_01.pdf
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12th January 2013, 04:02 PM  #39  
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Quote:
No, I'm not considering either opamp for an IV converter for a DAC. The IV converter I have is based on the LME49710.
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12th January 2013, 04:08 PM  #40 
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Out of that exNational range the only part I'd recommend for I/V duty would be the LME49713 because its CFB therefore no LTP to suffer the assault of all that RF.
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