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LVDS interface loop back function Disclosure Number: IPCOM000015836D
Original Publication Date: 2002-May-01
Included in the Prior Art Database: 2003-Jun-21
Document File: 2 page(s) / 51K

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LVDS interface loop back function

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LVDS interface loop back function

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.

Because most video graphics chips have on-chip LVDS drivers, this loop back test circuit can be


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embedded into those chips. In that case, this function can be implemented practically with no additional cost or no additional card space.


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