Mismatch Between AD9144 DAC Model Output and Expected SSB Output

Dear all,

Introduction:

We are modeling the digital backend and RF frontend of a wireless communication system.

As part of my task, I am focusing on the transceiver (xcvr) connection between the digital and analog domains.

While looking for ready-made block models for FMCDAQ2, I couldn’t find any.

However, I came across the AD9144 and AD9680 MATLAB models on Analog Devices website:

https://www.analog.com/en/resources/simulation-models/mathworks-behavioral-models.html

Setup:

From the datasheet (functional block diagram on page 5), I assumed the AD9144 model simulates the entire digital path,

including interpolation stages, up to the analog output from the DAC.

AD9144 model accepts complex input and produces complex output, which cannot be changed.

By referring to the datasheet (page 69), the complex input corresponds to I_DATA and Q_DATA, and the complex output corresponds to OUT_I and OUT_Q.

I ran the provided example model simulation to make sure there are no issues in files.

I then configured the model parameters for my application as follows:

• Data Rate: fdata = 300e6 (default was 1.06e9)
• Input Frequency: infreq = 10e6 (default was 163.1e6)
• Interpolation: l = 2 (unchanged)
• NCO Frequency: nco_freq = 75e6 (default was 0)

The model files are attached below. I used MATLAB 2024a for this simulation.

AD9144_Model.zip

The Problem:

Based on the complex modulation, I expect the output to show a Single Sideband (SSB) at 85 MHz (NCO + input frequency).

However, the spectrum analyzer shows Double Sideband (DSB) with components at 85 MHz and 65 MHz (NCO ± input frequency).

Given that the SEL_SIDEBAND control is supposed to select either the Upper Sideband (USB) or Lower Sideband (LSB), the DSB output is unexpected.

Input Spectrum: Shows a component at 10 MHz (input signal) and another at 0 Hz (bias).

Output Spectrum: Shows components at 85 MHz and 65 MHz, indicating DSB instead of the expected SSB.

Question:

Where could the problem lie? Is my understanding of the model or SSB behavior incorrect, or is there an issue with the AD9144 MATLAB model itself?

Any advice or clarification would be greatly appreciated.

Thank you for your support!