Why Forward Couplers Fall Short for Aggressor Injection in SERDES Testing
Rethinking Aggressor Injection: Skip the Forward Couplers
Forward couplers are often proposed for aggressor signal injection in SERDES testing—but they introduce fundamental limitations that make them unsuitable for accurate crosstalk modeling. In real-world backplane and serial link systems, forward couplers are not present. These systems are inherently wideband, and their transmission characteristics—defined by PCB traces, vias, and dielectric loss—are vastly different from what a directional coupler can emulate.
Crosstalk behavior in practical PCB systems is shaped by dielectric and conductor losses, along with layout-specific factors like via structures and connector transitions. These are critical variables for accurate Channel Operating Margin (COM) and serial link analysis, and none of them are captured using forward couplers.
Instead, consider using a purpose-built PCB crosstalk platform like XTALK-56. It’s designed to replicate realistic inter-symbol interference (ISI) and crosstalk characteristics across a range of channel types.
XTALK-56 includes:
- True PCB-based crosstalk coupling
- Via and backplane/connector emulation
- Return loss degradation structures
- Support for simultaneous clock and data interference
By modeling loss and crosstalk together, XTALK-56 allows engineers to quantify how these impairments affect transmission reach and perform SERDES design of experiments (DoE) with precision.
Crucially, adding noise to the RX input is not crosstalk—it’s just noise. Forward couplers inject deterministic jitter profiles that don’t match the stochastic nature of real PCB crosstalk. XTALK-56, by contrast, introduces jitter in a way that reflects actual high-speed PCB transmission paths.
If your goal is to evaluate the true impact of crosstalk on SERDES performance, I strongly recommend exploring XTALK-56 over any forward coupler-based approach.
