Hello How big is the analog output bandwidth of the AD9144 DAC?I would it use on the second or third nyquist zone for generating signals in the bands of 2...2.5 or 3.2...3.6GHz.for example:fullscale CW @ 800MHz and 2.8GS/s --> according to nyquist the image carrier would appear at (fs/2)+(fs/2-fc), in this case at 2GHz. How much output power would I have at 2Ghz in this case relatec to f0=0dB?Best regards
Hi Tobias Batt,
The AD9144 is not spec'd above 500MHz in the datasheet (which is not at all to say that it cannot operate above 500MHz).
In recent RF DACs (AD916x, AD917x, etc) we post the s-parameters of the analog output which defines the maximum analog BW. The limitation is then how well you can impedance-match to the balun at the output.
sinx/x roll-off is predictable and will always limit power above Nq1. Just plot sin(x)/x so that the nulls fall on Fs/2.
In your example you mention "CW at 800MHz". Note that the datarate of the SERDES link is max ~1060MSPS, and so the instantaneous BW (iBW) is 530MHz * %BW of the interpolation filter (80% for IQ interp in most DACs). This limits Fout to DC-530MHz*0.8, unless you use the NCO to shift the iBW across the analog BW of the output.
Even then the 2-3.6GHz is rather wide and running at lower Fdac (2.8GSPS) will complicate freq planning and filtering.
Consider the AD9171/3 instead? It can clock the DAC near 12GSPS and at a similar price point. The difference is that only two DAC cores are available. But take a look at the output mux ("modulator switch") which can split the samples into I and Q, each to its own DAC. it may save you a modulator.
The AD9173 at 12GSPS can also generate the full RF spectrum directly (pardon the pun).