Part Number:ADS54J60EVM
I'm using the ADS54J60EVM REV C. The analog input circuit uses two Mini-Circuits ADT-1WT+ transformers to convert a single ended input to the ADC's differential input. I have not modified the EVAL board and am running the ADC at 614.4MSPS. I'm using the Xilinx JESD IP in a third party FPGA board to collect the ADC data. I then calculate RF power from the ADC samples. I'm using a sig gen to put input an sine wave to the ADC. As I change the RF input frequency from say ~30MHz up to ~290MHz, I see a little over 3dB drop in the power calculated from the FFT. If I continue to raise the RF frequency into my second nyquist zone, the calculated RF power continues to drop and gets to ~7dB down at ~290MHz. Checked the sig gen and it's output power is constant over those frequencies.
From what I can see the ADC itself doesn't have this much roll off through this frequency range. Am I seeing the response of the transformer input circuit? The only info I can find is one sentence in the EVAL boards, users manual.
"Transformer-coupled signal input network allowing a single-ended signal source from 0.4 MHz to 800 MHz"
But I didn't think it would be greater than 7dB down at 600MHz. I've been going through the ADC's registers and can't see what could be doing this. I tried programming it for DC coupled input but that had no effect.