A general purpose 1149.4 IC with HF analog test capabilities

This paper describes a general purpose IC intended for improving the testability of mixed-signal circuit boards and for investigating enhancements to the IEEE 1149.4 mixed-signal test bus. The 20-pin IC makes it possible to measure the impedance of 9 board-level circuit nodes via a 2-wire analog bus, and to monitor high frequency signals (HF>10 MHz) in continuous or sampled time. The IC design, performance trade-offs, and measured performance are discussed. Impedance measurement accuracy (±5 ohms for first samples) was shown to be limited primarily by function pin series resistance R_COM; a simple technique for measuring its value is described. Lastly, results for a demonstration circuit board, and software available from many vendors, are presented