Adjustable current mode differential amplifier for multiple bias point sensing of MRAM having diode isolation

摘要

An adjustable current mode differential sense amplifier is provided. The amplifier is disposed to be in communication with a selected memory cell and a reference cell having a predetermined value. The amplifier is able to sense current and voltage changes associated with the selected memory cell and compare them to current and voltage changes associated with the reference cell. The operating point of the sensing amplifier may be changed by modifying threshold voltages related to the back gate bias applied to selected transistors in the amplifier. This adjusting capability enables currents or voltages of the sense amplifier to be set when a first bias voltage is applied to a selected memory cell in order to maximize the sensitivity of the amplifier. When a second bias voltage is applied to the memory and reference cells in order to determine the memory cell value, the amplifier is able to sense slight changes in the currents or voltages associated with the selected memory cell and the reference cell and compare them to determine the state of the memory cell. This increased sensitivity enables the amplifier to have a substantially increased dynamic range without introducing components that might adversely affect the memory circuitry parameters. The memory cell array being sensed has current control element isolation. An isolation voltage is applied to all current control elements in unselected memory cells. The isolation voltage is applied so as to reverse bias the current control element when the first bias voltage and the second bias voltage are applied to the memory cell and the reference cell.