| 摘要 |
SYSTEM FOR PRINTED CIRCUIT BOARD TESTING A system is described for connecting a printed circuit board (PCB) under test to a digital anslysis unit to permit verification of the functional behavior of the PCB. A bed-of-nails (BON) fixture is employed, allowing access to internal circuit nodes of the PCB. Controlled-impedance wiring, terminated in its characteristic impedance at the test electronics, allows high speed signals to be communicated without degradation from the unit under test (UUT). Excessive dynamic loading of the UUT circuit nodes is avoided by employing isolation resistances at each BON probe. The potentially large number of UUT signals to be monitored is multiplexed down to a smaller number of lines more readily accommodated by the digital analysis unit. The selected signals from the UUT are processed in a wide-band asynchronous manner by the test electronics in such a way that uniform delay of all signals through the multiplexer is achieved. The digital analysis unit is able to monitor the operation of the UUT just as well as if neither the BON nor any intervening electronics were present. The high-speed functional behavior of the PCB itself remains essentially unaffected by the presence of the BON, test electronics and digital analysis unit. |
