Noise-shaping sense amplifier for MRAM cross-point arrays

A sensing technique using a voltage-mode architecture, noise-shaping modulator, and digital filter (a counter) is presented for use with cross-point MRAM arrays and magnetic tunnel junction memory cells. The presented technique eliminates the need for precision components, the use of calibrations, and reduces the effects of power supply noise. To obviate the effects of cell-to-cell variations in the array, a digital self-referencing scheme using the counter is presented. Measured experimental results in a 180-nm CMOS process indicate an RMS sensing noise of 20 μV for a 5-μs sense time. Further increases in sense time are shown to increase the signal-to-noise ratio. The current used by the sense amplifier and counter was measured as 10 μA when running at 100 MHz or 10 mA when 1000 sense amplifiers are used with a memory subarray having 1000 bitlines.