A memory circuit including at least one memory cell connected to a bit line. The memory circuit further includes a means for providing a bit line reference voltage VBLref to the bit line. A VBLref/VDD ratio of the bit line reference voltage VBLref to a power voltage VDD is adjustable corresponding to a change of the power voltage VDD, and the VBLref/VDD ratio ranges from about 0.4 to about 0.53.