This paper first defines signal line fault detection testability measure (FDTM) for stuck-at-0 and stuck-at-1 faults. The FDTM is obtained from signal line's 0, 1-controllability and observability measures. This measure is analyzed in terms of the relationships between FDTM and undetected faults under the condition of the D-algorithm ATPG program execution for a certain time. Then, node (element/functional block) testability measure is defined from node's input 0, 1-controllability and observability measures. This measure is also evaluated in terms of the relationships between node testability measure regions and node fault coverage under the condition of the ATPG program execution for a certain time. Finally, the proposed testability measures applications in early design phases and test generation systems are discussed.

This paper describes an optimal logic partitioning/test points setting by using testability measures in large digital circuits. First, signal lines' testability measures (controllability and observability) in a circuit are computed. Next, the circuit is transformed into a network which consists of nodes (corresponding to circuit elements) and arcs (corresponding to signal lines). Then, after the arcs' capacity is defined as a function of the testability measures, the original logic partitioning/test points setting problem for the circuit is transformed into that for the maxflow in the network flows. This problem is solved by using the maxflow/ mincut theorem. Finally, it is shown that a simple logic circuit is considered using the proposed method.

40 Gbit/s optical transceiver using a novel OTDM MUX module has been developed. OTDM (Optical-Time-Division-Multiplexing) MUX module, the core component of the transmitter, consisted of a optical splitter, two electro-absorption (EA) modulators and a combiner in a sealed small package. As the split optical paths run through the "air" in the module, greatly stable optical phase relation between bit-interleaved pulses could be maintained. With the OTDM MUX module, the selection between conventional Return-to-Zero (conventional-RZ) format and carrier-suppressed RZ (CS-RZ) format is performed by slightly changing the wavelength of laser-diode. In a receiver, 40 Gbit/s optical data train is optically demultiplexed to 10 Gbit/s optical train, before detected by the O/E receiver for 10 Gbit/s RZ format. Back-to-back MUX-DEMUX evaluations of the transceiver exhibited good sensitivities of under -30 dBm measured at 40 Gbit/s optical input to achieve the bit-error-rate (BER) of 10-9. Another unique feature of the transceiver system was a spectrum switch capability. The stable RZ and CS-RZ multiplexing operation was confirmed in the experiment. Once we adjust the 40 Gbit/s optical signal to CS-RZ format, the optical spectrum would maintain its CS spectrum shape for a long time to the benefit of the stable long transmission characteristics. In the recirculating loop experiment employing the OTDM MUX transceiver, the larger power margin was successfully observed with CS-RZ format than with conventional-RZ format, indicating that proper encoding of conventional-RZ and CS-RZ was realized with this prototype transceiver. In the case of CS-RZ format, the error free (BER < 10-9) transmission over 720 km was achieved with the long repeater amplifier span of 120 km.