Issue link: https://iconnect007.uberflip.com/i/1538269
AUGUST 2025 I DESIGN007 MAGAZINE 23 controller and memory is too compact, then trace tuning becomes a challenge; too far, and signal propagation delays increase. In traditional high-speed design workflows, tim- ing specifications and simulation results guide the establishment of placement and routing constraints. With a given delay constraint, designers can man- age signal integrity by controlling the PCB trace topology across different interface components. Figure 2 illustrates the placement requirements for a DDR2 controller and memory chips, along with the 1.8V power plane. However, this applies to all memory interfaces. The placement guide aims to limit maximum trace delays and facilitate rout- ing and via placement challenges. It is important to note that this placement does not specify whether these devices are positioned on the top or bottom of the board. The DDR circuitry region must be isolated from other signals to prevent interference while main- taining a common ground plane. A designated keep-out zone, as shown in Figure 2, can achieve B E YO N D D ES I G N ▼ F i g u re 3 : D i f fe re n c e b et we e n t h e s e r i e s te r m i n ato r at t h e s o u rc e a n d l o a d . this. The 1.8V power plane should encompass this entire region and non-DDR signals should be kept outside of it to maintain signal integrity and proper operation. Also, the placement of series termina- tors, when required, can present layout challenges. In the absence of a termination at the far end of the trace, the series terminator must be positioned to effectively absorb the full reflection returning from the load. Figure 3 illustrates the difference between plac- ing a series terminator near the source, which is common, and at the far end near the load, which is generally not advised. Both placements serve to absorb reflections before they can propagate along the trace multiple times. However, the far- end termination tends to produce more waveform distortion, while the near-end termination results in a cleaner signal. Additionally, parallel termi- nation may be required to address VTT pull-up. These are typically placed at the end of a daisy chain to pull the signal up to VTT, the reference voltage for DDR2. Proper placement at the end of the line is essential. Effective component placement is essential for maintaining high-speed sig- nal integrity, efficient power distribution, thermal man- agement, and ease of man- ufacturing. Coordinate this with stackup planning, which determines routing paths, impedance levels, and return current behav- ior. Some tools offer precise dielectric control to facilitate optimal placement of criti- cal components like clocks, SerDes, and DDR memory, reducing stub lengths, skew, and via count. Segregating nets based on voltage, rise time, and function—using route fences and signal layer keep-outs—helps mitigate crosstalk and EMI. Addition- ally, managing component