Bipolar detection for cross-tie memories

A new method of cross-tie data bit detection which produces bipolar output signals (positive for "ones" and negative for "zeroes") is described. It eliminates the pedestal voltage and the need for a threshold to distinguish between "ones" and "zeroes", and reduces temperature stability requirements on memory elements and sensing circuits. The new method provides a more reliable detection function in memory systems compared to that of unipolar signal detection and is applicable to both serial access and random access crosstie memories. Bipolar signals are obtained by proper design of the magnetoresistive detector region of the film element and by applying a magnetic bias field alongs its hard axis during readout. Experimental data from both serial and random access memory devices and analysis of a theoretical model for the magnetization, bias field and sensing current relationships are presented.