1. Field of the Invention
The invention relates in general to a biasing and shielding circuit, and more particularly to a shielding circuit applied in a source-side sensing memory.
2. Description of the Related Art
Along with increasing development of technology, non-volatile memory, such as flash memory, has been wildly used in electronic product. For the reading operation of memory data of a flash memory device, a sensing circuit is used to sense a cell current of a target cell for determining the memory data value stored in the target cell. Referring to FIG. 1, a circuit diagram of a cell matrix of a traditional flash memory device is shown. When a cell Ca is accessed, the cell current I1 of the cell Ca should be sensed so as to determine the data value stored in the cell Ca. When sensing, a sense circuit 100 is coupled to the cell Ca. Due to that cell current I1 is hard to be sensed and shielded, a sense current I2 flowing to the sense circuit 100 is sensed instead and the sense current I2 is used to know the magnitude of the cell current I1 of the cell Ca for the operation of sensing. The cell current I1 and the sense current I2 satisfied an equation:I1=I2+I3
I3 is a leak current bypassing through the cell Cb, which is adjacent to the cell Ca. The leak current I3 will affect the preciseness of the sense current I1 and the correctness of the data value sensed by the sense circuit 100. The less difference of cell current and sensing current is, the more precisely the sense circuit 100 performs. We define the difference of cell current and sensing current to be error current. Therefore, how to design a flash memory circuit having small error current and precise data value sensing result has become an important goal to achieve.