DAC38RF86: Complex Modulated Carriers

Brad,

If sounds like you have four independent bands that you need to transmit at once. The dual band digital upconverter (DUC) per DAC channel will allow you to do four total bands. With 250 MHz each, you'll need a complex input rate of at least 312.5 Msps (due to 80% passband of complex interpolation filters). If 24x interpolation is used, then the minimum output sample rate is 7.5 Gsps. If you want 8 Gsps output rate, then you could do 333.33 Msps input rate (8000/24 = 333.33). Higher input rates are allowed as well, for instance at 8 Gsps with 16x interpolation your input rate is 500 Msps, supporting 400 MHz per carrier. See table 9 in the datasheet for allowed modes. If you do need all four bands at once (using all four DUCs), then you should look at the modes with 2 "IQ pairs per DAC". For instance, mode 88210 (2 TX) with 16x interpolation would allow four independent modulated signals of up to 450 MHz each (562.5*0.8=450). You can also sum all four DUC outputs together and output from a single DAC channel using the multiband summation block.

For the PLL, you'll need to verify that the final output rate is supported by the VCO. The rates supported by the VCO are provided in the PLL/VCO Electrical Characteristics table. You can choose the final output rate (that fits in the supported VCO range) and then back calculate the required input rate (based on the interpolation used) or choose the input rate and forward calculate the final output rate (and verify if it fits in the VCO range).

For more VCO options see the DAC38RF89. It has a differential output, so external baluns are required, but it does have VCOs centered at 5 GHz and 7.5 GHz. These are not the "GSM PLL" though, so phase noise will be slightly degraded compared to DAC38RF86.

Regards,
Matt Guibord