A TIME A-D CONVERTER LSI FOR ACCURATE MEASUREMENT OF MULTITIME-INTERVAL BY DIGITAL PROCESSING

The authors previously have reported on the ''ring gate delay'' system which digitizes the infinitesimal time interval with the delay time o f the inverter as the resolution, without using the high-speed referen ce clock [1]. A problem then is the improvement of the accuracy since the delay time of the inverter depends on various conditions such as t he ambient temperature, the supply voltage, and the fabrication condit ion. To remedy this point, an LSI is constructed and the delay time of the original circuit is monitored continuously using the quartz oscil lation clock of st relatively low frequency as the reference, and the time to be measured is digitized with a high accuracy based on the del ay time. In this system, it is not necessary to control the delay time , which makes it possible to utilize the shortest delay time. By a sin gle measurement process using a single input port, up to four pulses c an be measured consecutively, If the pulse interval to be measured in less than the specified time, the pulses are combined into a single pu lse and an incorrect operation is prevented. In this study, a sample d evice is constructed by a 1.5-mu m CMOS process. The measurement range of 2200 ns (12 bit) with the time resolution 0.5 ns is achieved using the supply voltage of 5 V, The minimum pulse interval that can be mea sured is 55 ns(at 25 degrees C). The reference clock used is 2 MHz, Th e number of transistors is 15,000 and the chip size is 3.5 mm x 3.8 mm . The constructed LSI is composed totally of digital circuits. The ope ration is robust against the environmental condition, and a stable ope ration is realized for the ambient temperature of -35 to 140 degrees C .