Browse Prior Art Database

LVDS interface loop back function

IP.com Disclosure Number: IPCOM000015836D
Original Publication Date: 2002-May-01
Included in the Prior Art Database: 2003-Jun-21
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Abstract

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.

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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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