A memory controller includes a voltage driver and a voltage comparator. The voltage driver applies a variable voltage to a selected line of a crossbar array to determine a first measured voltage that drives a first read current through a selected memory cell of the crossbar array. The voltage driver applies the variable voltage to the selected line to determine a second measured voltage that drives a second read current through the selected memory cell. The voltage comparator then determines a voltage difference between the first measured voltage and the second measured voltage and to compare the voltage difference with a reference voltage difference to determine a state of the selected memory cell. The crossbar array comprises a plurality of row lines, a plurality of column lines, and a plurality of memory cells. Each memory cell is coupled between a unique combination of one row line and one column line.

A method of obtaining a dot product using a memristive dot product engine with a nulling amplifier includes applying a number of programming voltages to a number of row lines within a memristive crossbar array to change the resistance values of a corresponding number of memristors located at intersections between the row lines and a number of column lines. The method also includes applying a number of reference voltages to the number of the row lines and applying a number of operating voltages to the number of the row lines. The operating voltages represent a corresponding number of vector values. The method also includes determining an array output based on a reference output and an operating output collected from the number of column lines.

The present disclosure relates to reference and sense architecture in a cross-point memory. An apparatus may include a memory controller configured to select a target memory cell for a memory access operation. The memory controller includes word line (WL) switch circuitry configured to select a global WL (GWL) and a local WL (LWL) associated with the target memory cell; bit line (BL) switch circuitry configured to select a global BL (GBL) and a local BL (LBL) associated with the target memory cell; and sense circuitry including a first sense circuitry capacitance and a second sense circuitry capacitance, the sense circuitry configured to precharge the selected GWL, the LWL and the first sense circuitry capacitance to a WL bias voltage WLVDM, produce a reference voltage (V.sub.REF) utilizing charge on the selected GWL and charge on the first sense circuitry capacitance and determine a state of the target memory cell based, at least in part, on V.sub.REF and a detected memory cell voltage V.sub.LWL.

A method to access two memory cells include determining a first cell current flowing through a first memory cell by subtracting a sneak current associated with the first memory cell from a first access current of the first bitline and determining a second cell current flowing through a second memory cell in the first bitline or a second bitline by subtracting the sneak current associated with the first memory cell from a second access current of the first bitline or the second bitline.

A sense amplifier circuit includes a sampling capacitor coupled to the input of an inverting amplifier. The output of the inverting amplifier is coupled to a transistor that includes a current terminal. The memory read operation includes two phases. During a first phase, a terminal of the capacitor is coupled to a first cell. During a second phase, the terminal of the capacitor is coupled a second cell.

In one embodiment, a sense amplifier circuit includes two current paths. Each path includes a transistor configured as a current source during a memory read operation and a second transistor. During the first phase of a memory read operation, the first current path is coupled to one cell and the second current path is coupled to a second cell. The sense amplifier circuit includes a capacitor that during a first phase of a memory read operation, is coupled between two corresponding nodes of the two paths to store a voltage difference between the two nodes. During the second phase, the cell/current path couplings are swapped and the capacitor is coupled to the control terminal of one of the second transistors to control the conductivity of the transistor for adjusting a voltage of an output node to indicate the value of the data being read.

Methods, systems, and devices for varying-polarity read operations for polarity-written memory cells are described. Memory cells may be programmed to store different logic values based on applying write voltages of different polarities to the memory cells. A memory device may read the logic values based on applying read voltages to the memory cells, and the polarity of the read voltages may vary such that at least some read voltages have one polarity and at least some read voltages have another polarity. The read voltage polarity may vary randomly or according to a pattern and may be controlled by the memory device or by a host device for the memory device.

A method of determining a current in a memory element of a crossbar array is described. In the method, a number of pre-access operations are initiated. Each pre-access operation includes discarding a previously stored sneak current, determining a new sneak current for the crossbar array, discarding a previously stored sneak current, and storing the new sneak current. In the method, in response to a received access command, an access voltage is applied to a target memory element of the crossbar array and an element current for the target memory element is determined based on an access current and a stored sneak current.

In one example in accordance with the present disclosure a method of determining a resistance state of a memristor in a crossbar array is disclosed. In the method, a combined reference-sneak current is determined based on a reference voltage, a sense voltage, a non-access voltage, and a voltage applied to a target row line. Also in the method a combined read-sneak current is determined based on a read voltage, a sense voltage, a non-access voltage, and a voltage applied to a reference row line. A resistance state of a target memristor is determined based on the combined reference-sneak current and the combined read-sneak current.

A memory includes a pair of sense amplifiers where the pair of sense amplifiers perform a multiphase memory operation to read data from two memory cells. Each sense amplifier includes two current paths. During a first phase of the memory read operation, one of the two sense amplifiers provides current through both a first memory cell and a first reference cell and the other sense amplifier of the two provides current through both a second memory cell and a second reference cell. The reference cells each have different resistance values. During a second phase of the memory read operation, one of the sense amplifiers provides current through both of the first memory cell and the second reference cell and the second sense amplifier provides current through the second memory cell and the first reference cell.