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jmltinc 4th October 2012 11:08 AM

Two DAC Concepts
 
Hello All,

Please help me understand a few DAC concepts so I may move on! I have a CS4397...

Why is there a choice of two VD sources - 3V and 5V? Is there an advantage or disadvantage to either choice?

The offset voltage. My understanding is this is to allow single-supply operation. Is this true? Can offset be minimized without losing SQ?

Thanks,
-John

Ken Newton 4th October 2012 01:24 PM

I didn't find a CS4387 on Cirrus' website. I'll assume you mean the, CS4397.

The choice of 3V or 5V digital supply voltage (VD), will be determined by the supply voltage requirement of the digital logic feeding the DAC chip. This is to provide flexibility at the DAC chip for accepting the logic signal levels from either a 3V, or a 5V preceding logic device.

Yes, the analog output voltage is necessitated by the unipolar aspect of the power supply. You generally have two options for dealing with this offset. you could directly feed the differential outputs to a differential buffer, which is usually what's recommended in such DAC datasheets. Or, you could instead block the D.C. offset utilizing coupling capacitors, but then you would still want to send the now A.C. coupled differential output signals to a buffer having differential inputs.

naniking 4th October 2012 01:38 PM

Quote:

Originally Posted by jmltinc (Post 3189643)
Hello All,

Please help me understand a few DAC concepts so I may move on! I have a CS4387...

Why is there a choice of two VD sources - 3V and 5V? Is there an advantage or disadvantage to either choice?

The offset voltage. My understanding is this is to allow single-supply operation. Is this true? Can offset be minimized without losing SQ?

Thanks,
-John

I think, in my concept:

- Some chips are using 3.3V, such as WM8741 which is DAC decoder.

- USB chips always using 5V that it can communicated with computer.

Just know CM6631.

jmltinc 5th October 2012 08:55 AM

Yes, the DAC is a 4397. I edited the posting.

Thanks for the replies. I spent a lot of time trying to nail down what was very simple.

-John


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