Re: AD9850 DAC output current boost


Thanks Jim,

Yes I have the APP Note on using the FET to modulate the DDC output.


Mike K5ESS


From: PHSNA@... [mailto:PHSNA@...]
Sent: Tuesday, December 08, 2015 2:52 PM
To: PHSNA@...
Subject: [PHSNA] Re: AD9850 DAC output current boost



I haven't played with R-set. There is a graph in the data sheet showing that the best spurious free dynamic range is at an I-out of 10 mA. Going to 20 mA degrades SFDR by a couple of dB or so. Would only add 5 mA to the average current, so I doubt heating would be an issue. Given the I-supply is around 80 mA, it would be about a 10% increase in dissipation.

Look in the Links area here on the group for an app note about replacing R-set with an FET to amplitude modulate the output (could be the basis of AGC)

Jim, N5IB

---In PHSNA@..., <k5ess.nothdurft@...> wrote :
The AD9850 datasheet says that the max DAC output current is 20mA which can be achieved by reducing the value of the R-SET resistor from 3.9k to 1.95k ohms.  Has anyone tried this and if so were there any deleterious effects? 

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