Abstract: An apparatus and method for locating light sensitive circuit design flaws on an integrated circuit chip comprises placing the integrated circuit chip on a load board, which is coupled electrically with a tester to supply operating power to the chip device. The current used by the chip device is continuously measured. A stereoscopic microscope is used to direct a spot of light through one of the eyepieces of the microscope onto the upper surface of the chip; and the spot of light is moved along a predetermined path to scan the surface of the chip. Through the other eyepiece of the microscope, the location of the spot of light is observed. When the measured current drain undergoes changes, as the spot of light impinges on the chip, the location is noted. The quadrant or other area of the chip, in which the change of current consumption occurred as a result of the spot of light, then is scanned a second time with a smaller spot of light; and the process is repeated.

Abstract: A digital-to-analog converter of the R/2R ladder type is composed of two individually asymmetric ladders symmetrically coupled to a differential amplifier. Switch means in the shunt arms of the ladders are controlled so that the same number of shunt arms are connected to each of a pair of input or output nodes irrespective of the value of the controlling digital signal. The most significant shunt arm in each ladder may be configured as an equivalent of that part of the respective ladder extending from the respective stage node towards the least significant end of the ladder.