MEMS Switches and SiGe Logic for Multi-GHz Loopback Testing

We describe the use of microelectromechanical system (MEMS) switches and SiGe logic devices for both passive and active loopback testing of wide data buses at rates up to 6.4 Gbps per signal. Target applications include HyperTransport, fully buffered DIMM, and PCI Express, among others. Recently introduced MEMS devices provide >7 GHz bandwidth in a very small package (needed to handle wide buses). SiGe logic supports >7 Gbps signals when active shaping of the waveform is required. Each loopback module typically supports between 9 and 16 differential channels. Multiple cards are used to handle applications with very wide buses or multiple ports. Passive cards utilize MEMS for switching between the loopback (self-test) mode and traditional automated test equipment (ATE) source/receiver channels. Future active card designs may provide additional waveform-shaping functions, such as buffering, amplitude attenuation/modulation, deskew, delay adjustment, jitter injection, and so forth. The modular approach permits precalibration of the loopback electronics and easy reconfiguration between debug or characterization testing and high-volume production screening