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rhickling
Newbie
Newbie
733 Views
Registered: ‎09-08-2020

RFSoC DAC Output Power

According to Table 125 in Document DS926 the maximum current that the RF DAC can put out is 36 mA.  Driving a 100 ohm load (I am assuming that means 2 x 50 ohms in complementary fashion) that means the peak-to-peak voltage for each side of the complementary pair is 36mA x 50 ohm = 1.8Vpp.  Differentially that would be 3.6 Vpp (which should result in a total power into 100 ohms of 64.8 mW or 18.1 dBm).  Yet the same table quotes the maximum available power into 100 ohms as 5 dBm.  Since sin x/x cannot account for this much discrepancy, can you explain this apparent contradiction?

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zhendon
Community Manager
Community Manager
672 Views
Registered: ‎08-30-2011

Hi @rhickling 

It is 32mA mode and 20mA mode.

Output is differential so that means 16mA common and 16mA for differential output for 32 mA mode . Vppd would be 16 mA x 100 ohm = 1.6V. Prms would be calculated as (vpk/root2)^2/100Ohm =  (0.9/root2)^2/100 =  0.0032W

Pdbm would be 30+10log Prms/1W =  5dBm

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rhickling
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Newbie
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Registered: ‎09-08-2020

This still seems inconsistent to me … if as you describe the common mode current for each of the two complementary outputs is 16mA and the differential amplitude is 16mA (32 mApp), that means each of the outputs only swings +/- 8 mA, (between an output max of Iout+ = 24mA Iout- = 8mA and an output min of Iout+ = 8 mA Iout- = 24 mA).  Is that actually how the DAC behaves?

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