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Bit Line Offset Circuit

IP.com Disclosure Number: IPCOM000044491D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Morency, DG: AUTHOR [+2]

Abstract

Margin testing on random-access memories (RAMs) is performed to determine exactly how much the signal can be reduced before the sense amplifier flips in the wrong direction. This article describes a technique for performing margin tests on RAM arrays which also serves as an accurate signal measurement technique. Using the resistances 11, 12 shown in the on-chip circuit, a one-volt change in the voltage VM will result in a 0.1-volt change in the bit line precharge voltage. The result is accurate incremental control of the bit line. Note that the precharge voltage for the dummy bit line 13 does not change while the bit line 14 precharge voltage is changed. The fixed offset of the precharge voltage between bit line 14 and dummy bit line 13 directly reduces the signal provided at the read time.

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Bit Line Offset Circuit

Margin testing on random-access memories (RAMs) is performed to determine exactly how much the signal can be reduced before the sense amplifier flips in the wrong direction. This article describes a technique for performing margin tests on RAM arrays which also serves as an accurate signal measurement technique. Using the resistances 11, 12 shown in the on-chip circuit, a one-volt change in the voltage VM will result in a 0.1-volt change in the bit line precharge voltage. The result is accurate incremental control of the bit line. Note that the precharge voltage for the dummy bit line 13 does not change while the bit line 14 precharge voltage is changed. The fixed offset of the precharge voltage between bit line 14 and dummy bit line 13 directly reduces the signal provided at the read time. Resistor 9R 12 is made up of a series combination of nine geometries identical to R 11. Polysilicon resistors are used and placed in close proximity to improve tracking. The result is a resistor ratio which is independent of wafer processing. This accurate control of the bit line voltage is also used as a signal measurement technique. Using this scheme eliminates the need to accurately monitor the bit lines since the point at which the sense amplifier flips in the wrong direction determines when the margin voltage change first exceeds the signal presented to the bit line. As a result, bit line source follower voltage sensing, which is difficult to calib...