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Old 17th January 2013, 05:08 AM   #91
qusp is offline qusp  Australia
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then of course we have the fact that depending on the frequency a resistor looks like an inductor, parasitic effects etc. its not so neat with this board due to the many holes punched in it. even with your ground strap, the lowest impedance ground might be somewhere you dont expect.

drilling a heap of vias may make matters worse, you need to think about where the loop area for each signal is.

actually saying ground flows one way and signal the other is not really correct, that is how it used to be viewed. electrons flow and electron holes flow, it is not as simplified as them flowing in opposite directions. conventional signal flow is not really the most accurate model it turns out, I think your explanation is a bit too neat.

but maybe best to think of it that way for now, just dont expect that just giving a return current a wire to travel on will mean thats the way it goes.

speaking of capacitance though, your ground strap and tape is making a nice little cap =)

I explained all of this in detail in a deleted post on hifiduino a couple of weeks ago.... even offering some mods /solutions. I was pretty negative towards the design, but isnt the fact that people have not even finished one before modding it heavily a sign that I was on the right track? I did try to offset it by offering ways to fix it for those who already had the board.

glt, almost nothing on this board could be called a very high frequency signal, its only barely RF on the clock lines. planes are the way to go vs striplines

the place that will be most critical will be the outputs to the IV resistor and the clock lines, as well as taking care where the i2c lines are.

the dac outputs will still have some high frequency components riding in the signal from the modulator, the ESS is pretty clean compared to some ∑∆ dacs, but still will have some. this is what the LPF is for in the opamp stage, skimming that off and its why a high slewrate opamp is preferred

Last edited by qusp; 17th January 2013 at 05:19 AM.
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Old 17th January 2013, 05:50 AM   #92
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speaking of capacitance though, your ground strap and tape is making a nice little cap =)
Care to calculate the value of the added capacitance between the ground strap and the power lines ? The "dielectric" is one layer of common insulation tape, plus the pcb coating.
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Old 17th January 2013, 05:55 AM   #93
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Gents I was reading this article earlier today and thought of you

return path discontinuities

It might help the understanding of return currents and choices made and also gives some suggestions for location of extra caps when the reference plane changes

I like your quip KK
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Old 17th January 2013, 06:06 AM   #94
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Gents I was reading this article earlier today and thought of you

return path discontinuities

It might help the understanding of return currents and choices made and also gives some suggestions for location of extra caps when the reference plane changes

I like your quip KK
Good read, thanks. I hope they don't mind me quoting, "Note, that if the two reference planes are of the same type (either both power, or both ground) you can put a via (ground to ground or power to power)....... immediately adjacent to the signal via."

In other words, for this design with two ground planes, I should add vias near any signal path vias.

In this case, the through hole resistors for I/V are prime candidates for a via close by.
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Old 17th January 2013, 06:14 AM   #95
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I've updated the blog. In fact there are 5 "bridges" to install.

For the controller, read the "intro" page and the "code" page in my blog. Then buy the components, download the code, connect to DAC and done.

Family first, most of the time, but sometimes I sneak out to my shop :-)
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Last edited by glt; 17th January 2013 at 06:16 AM.
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Old 17th January 2013, 06:16 AM   #96
qusp is offline qusp  Australia
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I like your quip KK
yeah, yet i'm sure he'll gladly accept help from us.... its only when its something they dont want to know that we become ********
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Old 17th January 2013, 06:18 AM   #97
qusp is offline qusp  Australia
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Originally Posted by KlipschKid View Post
Care to calculate the value of the added capacitance between the ground strap and the power lines ? The "dielectric" is one layer of common insulation tape, plus the pcb coating.
dont be silly, it was a joke, though i'm sure there is a little bit there. layers of ground plane and power are often used in high frequency digital and RF design as planar capacitance designed right into the PCB, for high frequency transient storage, or decoupling VHF

Last edited by qusp; 17th January 2013 at 06:28 AM.
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Old 17th January 2013, 06:35 AM   #98
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Sorry, that was my misunderstanding. I'm used to jokes starting something like this - why are lesbians vegetarian ?

I think there's also a bit of a mis-communication generally. I'm not trying to build a perfect DAC. As the Irish joke goes, when you wanna get somewhere, you don't wanna start from here. I'm building this one as a budget DAC, say US$200, and wondering if it'll beat my dual AD1955 384Khz DAC.
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Old 17th January 2013, 06:55 AM   #99
glt is offline glt  United States
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t...just dont expect that just giving a return current a wire to travel on will mean thats the way it goes.
In this case, it does, otherwise it must travel around the power lines which is a mile away.
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Old 17th January 2013, 07:03 AM   #100
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GLT - how do you make it look better than mine every time ?! It's not fair. You even removed the screen in almost exact squares.

I'll read you 'duino stuff at the weekend.

Last edited by KlipschKid; 17th January 2013 at 07:06 AM.
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