I understand why reflections occur when there is an impedance mismatch on a single-wire transmission line. However, when we introduce a differential line, I am having trouble picturing what would occur in the following cases:
Imagine a transmission line with 100-ohm differential impedance and 50-ohm single-ended impedance. What would happen in each of these cases?
(1) There is a discontinuity where the differential impedance remains 100 ohms, but the single-ended impedance changes.
(2) There is a discontinuity where the differential impedance changes, but the single-ended impedance remains 50 ohms.
The reason this could be unavoidable in real-life design is due to restrictions on stackup and trace width/spacing that may be driven by other mandatory design requirements. If I have to design in either one of these types of discontinuities, I want to understand which is worse, and why.