Signal integrity consideration in high density digital Signal Processing boards

dasiaHigh-speed high-densitypsila digital Signal Processing (DSP) circuitry has become a necessity in almost every complex electronic product. The realization of such circuitry is almost always in form of multilayer printed circuit boards (PCB) having 10 to16 layers. In these PCBs, due to the compact network of signal carrying connections, unwanted noise and signal distortions are observed. These effects are minimized by taking appropriate care in PCB design stage. Designing a PCB that keeps the noise and distortion within acceptable limits is very important. This paper identifies the locations where careful signal integrity analysis is necessary and their possible effect on the performance. SAMEER has developed a DSP board of size 115times115 mm₂ with 2 tiger-SHARC processors and an FPGA with 500 K gates. All the discussions are presented with reference to the examples of this board. The paper presents various signal integrity (SI) plots of critical signals with a special emphasis on analog lines. The corrective action in such cases is also suggested.