1. Field of the invention
The present invention relates to voltage redoubling circuit, more particularly to, the voltage redoubling circuit operated at a low voltage such that a conducted memory cell can be quickly and accurately accessed via a single on-and-off signal rather than a plurality of pulse control signals.
2. Description of the Related Art
With rapid advance of manufacturing, memory devices are the inevitable essential electronic parts for many electronic products nowadays. When a memory cell is read, its operating method is to compulsorily turn on row bits and numeric bits. If the memory cell to be read is of conducted memory cell and operated in the low voltage region, there is either insufficient voltage for row address to turn on the memory cell or insufficient current despite sufficient voltage to turn on the same. In the aforesaid situation the information restored in the memory cell cannot be correctly accessed. And while operating at low voltage region and pumping the voltage of row address to an even higher voltage than the operating voltage, the information restored in the memory unit of conducted memory cell operated in the low threshold voltage can be correctly accessed. In the high operating voltage region there is no need to pump the voltage of row address even higher than the operating voltage because the high operating voltage is high enough so that the conducted memory cell at low threshold voltage can be turned on. Also in high operating voltage region, the device may suffer from damage if the voltage of row address is pumped to a voltage even higher than the operating voltage. As a result in low operating voltage region, the voltage of row address must be pumped up to a voltage higher than the operating voltage such that the conducted memory cell at low voltage can be certainly accessed. In the high operating voltage region, the voltage of row address does not necessarily be pumped to the voltage higher than the operating voltage, that is to say; the conducted memory cell at low voltage can be certainly read without pumping and thus the damage to devices can be also prevented. However, the conventional art as aforementioned will take a number of pulse control signals to lead to the desirable improved result. For the concern of hardware die size, multiple pulse control signals will lead to corresponding multiple control signal sources, such that the die size shrink scale is limited. Meanwhile, a plurality of pulses operated in a small area will also possibly lead to mutual interferences such that the circuit cannot function properly.
Therefore, there exists a solid demand for a voltage redoubling circuit, which uses only a single on-and-off signal rather than pulse control signals to enable the circuit such that conducted memory cell can be quickly and correctly read at low voltage operation region.