LVDS interface loop back function
Original Publication Date: 2002-May-01
Included in the Prior Art Database: 2003-Jun-21
LVDS interface loop back function This idea is to utilize terminated balanced transmission line of the LVDS as a loop back test path for the RAS purpose. LVDS used in personal computer LCD interface is a 100-ohm terminated balanced transmission interface(Fig.-1). It has loops formed by 4 sets of signal line, terminator, and signal line. By applying differential voltage to the loop and measuring the current as indicated in Fig.2, open fault or short fault of the line is detected. Fig-2 (a) is LVDS driver and receiver connected by a cable. (Without the loop back function implemented) Fig-2 (b) is loop back function implemented to Fig-2 (a). In Fig-2 (b), test function is disconnected by a pair of switches and the circuit works identical to Fig-2(a). In Fig-2 (c), loop back test is being done. R measure circuit is driving the differential LVDS interface line. Either AD convertor or simple window comparator may be used in the measurement.