AD HOC Testing of CMOS chip

Ad hoc techniques are used for testing an electronic circuit to identify the faults present in it. This technique is mainly used to test the registers present in the chip and is broadly classified into four types viz, Counter testing, Dividing the long counter, Multiplexer(Mux) based testing and Bus Oriented testing. Dividing the long counter is nothing but dividing the counter into separate counters and testing the same. This reduces the time required for testing. Counter testing is a predominant testing technique in which the reset pin is replaced by the test input so that the output for the given input can be determined. And with this value the difference between the expected output and the original output is calculated. If they both match each other, the device under test is working properly and we can say that there is no fault in that particular device. Else the fault is identified and rectified. In Mux based technique two devices are taken into account and are compared. Their outputs are finally compared with each other for fault analysis. Bus oriented testing deals with the Automatic Test Path Generation (ATPG), which is connected to the devices under test like RAM, ROM and I/O devices. Bus oriented testing is mainly practiced to check the faults in the data paths.

Underwater Communication - Features

Under water communications are defined below the water in oceans. They are used to transfer information to various nodes via cables placed under water. Modern underwater communication systems use either acoustic or optical techniques to transfer information. This technique was motivated by major scientific discoveries which enhanced cabled submersibles. Telephone cables pass through oceans to connect countries. With this communication technique the transmission of packets is more reliable. The data link layer protocols are used for flow control and error control mechanisms. The packets are generally longer than in the normal communication techniques. As it is an acoustic channel it has a varying bit error rate (BER), poor throughput efficiency and long waiting time. But the long waiting time is used well by the protocol layer. Aloha which is a Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) is used. Frequency, code or time division multiple access can be used for channel sharing. The data that are sent underwater are more reliable and secure. The modulation techniques used are Phase Shift Keying and Quadrature amplitude modulation. Phase and delay synchronizations are the prevalent measures undergone by this technique. Cables drawn are heavy, weighing above several hundred kilograms. It is very difficult to rectify the physical errors in cables. They are too hard to deploy. Research is going on for the deployment of nodes in the underwater communication.