Optimum Decoupling of Digital ICs

[Oli]

Application: AD1865N-K non-os dac, Kwak Asynchronous Reclocker

I have been reading a number of data sheets recently, but I keep encountering conflicting advice about decoupling ICs. I have a few questions someone might be able to help me with...

Q. Can I bypass VHC logic with a 220u OS-CON in parallel with a 0.1u ceramic? (Are these values appropriate?)

Q. Should I use resistors or inductors in the power supply lines of my VHC logic to further isolate each noise loop? (Which values?)

How does the situation differ with my OP627 Opamps?

[Guido Tent]

Originally posted by Oli

Q. Can I bypass VHC logic with a 220u OS-CON in parallel with a 0.1u ceramic? (Are these values appropriate?)

Q. Should I use resistors or inductors in the power supply lines of my VHC logic to further isolate each noise loop? (Which values?)

How does the situation differ with my OP627 Opamps?

Hi

These values will work in most cases.

Yes, you should use inductors, or preferably ferrite beads in series with the lines. In addition watch the Q of the whole decoupling network, otherwise it may resonate.

Opamps: I'd suggest seperate supplies, and 10 to 47 ohm in each supply line, and some decent audio grade lytics.

Take care of correct position of decoupling caps. Some more info can be found in an article I wrote while ago

http://httpd.chello.nl/~m.heijligers...decoupling.pdf

enjoy

[Elso Kwak]

Originally posted by Oli
Application: AD1865N-K non-os dac, Kwak Asynchronous Reclocker

I have been reading a number of data sheets recently, but I keep encountering conflicting advice about decoupling ICs. I have a few questions someone might be able to help me with...

Q. Can I bypass VHC logic with a 220u OS-CON in parallel with a 0.1u ceramic? (Are these values appropriate?)

Q. Should I use resistors or inductors in the power supply lines of my VHC logic to further isolate each noise loop? (Which values?)

How does the situation differ with my OP627 Opamps?

Hi Oli,
You might find all answers here (80 pages!):
http://www.analog.com/UploadedFiles/...520527817b.pdf

[Elso Kwak]

Hi Oli, I now realise that part of your questions may be my fault as I forgot to draw in the schematic the decoupling caps on the flip-flop IC's . Each one has 0.1µF ceramic cap directly at the powersupply pin (#14).
For me this goes without saying. Also there is a ferrite bead in the powersupply line between the oscillator and the logic IC's.

[fmak]

Opamps: I'd suggest seperate supplies, and 10 to 47 ohm in each supply line, and some decent audio grade lytics.

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Guido

I have often wonder why some manufacturers favour this, whereas others seem to favour lowest PS impedance.

Anyone done sonic evaluation of adding RC filters to opamp PS?

[jewilson]

Oli,

The OSCON types caps are very good also somtime you might need to use a .01uf instead of .1.

Elso Kwak,

That's a great application note, it's very uptodate.

[Guido Tent]

Originally posted by fmak
Opamps: I'd suggest seperate supplies, and 10 to 47 ohm in each supply line, and some decent audio grade lytics.

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Guido

I have often wonder why some manufacturers favour this, whereas others seem to favour lowest PS impedance.

Hi

I add resistors to dampen the decoupling. This may also be achieved by using lytics with high ESR

It is quite easy to simulate if your decoupling resonates or not

Ciao

[fmak]

I add resistors to dampen the decoupling. This may also be achieved by using lytics with high ESR

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What does this do to the sound?

[Oli]

Thanks folks!

Indeed a very good technical article Elso. I need to spend some time to digest at 80 pages.

I am currently using the following devices with your asynchronous reclocker:

Cho-Drop

The data sheet claims they are better than ferrites.

Has anyone else had any experience of these?

[jewilson]

Yes ferrites work well but you have to get the one for the correct frequency. So you have to select the right material. There are lots of possiblities with ferrites.