Memory devices typically include a plurality of memory cells, which may be arranged in an array of intersecting rows and columns. The location of each cell in the array may be indicated with an address, such as a row address and/or a column address. The memory cells may be read by selecting a row of memory cells with a corresponding row address. A bit of stored data may then be coupled from all or some of the columns in the addressed row.
Memory devices may store data using a variety of techniques. For example, dynamic random access memory (“DRAM”) devices may use memory cells that are essentially small capacitors that store data based on the amount of charge stored in the capacitors. When a memory cell is read, the memory cell may be coupled to a digit line so that the charge of the capacitor is shared with a charge of the digit line to which it is coupled. This charge sharing results in a small change in the voltage to which the digit line had been previously charged. A respective sense amplifier coupled to each digit line may be utilized to sense a small differential between the voltage on the digit line and the voltage on a complementary digit line. Voltage sense amplifiers have long been used in this manner to sense voltage differentials between complementary digit lines. However, voltage sense amplifiers may not function well over a wide range of power supply voltages, particularly at the low end of the range. For example, at low supply voltages the sense amplifier may not respond quickly enough to the voltage differential being sensed.
Another type of sense amplifier that may function better than voltage sense amplifiers in some cases, particularly at low supply voltages, are current sense amplifiers. Current sense amplifiers sense a differential in the current flow from complementary digit lines resulting from coupling one of the digit lines to a memory cell, such as a DRAM memory cell. However, at lower supply voltage, even current sense amplifiers may be unable to respond to a current differential with sufficient speed, and they may tend to incorrectly respond to noise signals, thereby producing invalid data results. This problem may be particularly acute as the electrical characteristics of electrical components used in current sense amplifiers may charge responsive to process, supply voltage and temperature variations.
USPTO Backgrounds
USPTO Backgrounds