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shawn_h
Visitor
Visitor
1,188 Views
Registered: ‎11-13-2018

RF SOC DAC output compliance range

What is the DAC output voltage compliance range (the minimum voltage with respect to ground at the DAC outputs which doesn't degrade performance)? I need to DC couple and level shift (towards ground) the outputs.

Thanks,

Shawn

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klumsde
Moderator
Moderator
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Registered: ‎04-18-2011

Hi Shawn

There are ways to DC couple and shift the DAC output. But it can be tricky not to degrade the DAC output performance. 

You have to ensure that the DAC has the correct 100ohm differential output load and then you have to ensure that the correct common mode voltage. 1.9v for 20mA and 2.1v for 32mA drive settings. 

I'll post a more detail response when I am back in the office tomorrow. 

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shawn_h
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Registered: ‎11-13-2018

Hi klumsde,

For the 20mA case, the common mode current would be 10mA, the supply voltage is 2.5V, and the pull up resistors are 50 ohms. This would result in a common mode voltage with no DC loading of 2.5V-10mA*50ohms=2.0V which is 0.1V above what you stated below. So are you saying that the DC loading while maintaining a 100 ohm differential impedance can reduce the common mode voltage by 0.1V maximum?

Thanks,

Shawn

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nima@silc.com
Newbie
Newbie
752 Views
Registered: ‎06-16-2019

Hello

Following up on this question for dc coupled mode of operation, I want to confirm that we need to externally bias the DAC output common mode voltage to 2.1V for the 32mA/3.0V term mode. Also the max DAC output swing will be 1.6V peak to peak differential resulting in a single ended swing of 2.1V +/- 400mV with an external 100ohm differential load.

Thanks!

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