CURRENT-MODE TECHNIQUES FOR HIGH-SPEED VLSI CIRCUITS WITH APPLICATION TO CURRENT SENSE AMPLIFIER FOR CMOS SRAMS

The speed of VLSI chips is increasingly limited by signal delay in long interconnect lines. A simple analysis shows that major speed improvements are possible when using current-mode rather than conventional voltage-mode signal transporting techniques. The key to this approach is the use of low-resistance current-signal circuits to drastically reduce the impedance level and the voltage swings on long interconnect lines. As an example, a simple four-transistor current-sense amplifier for fast CMOS SRAM's is proposed. The circuit presents a virtual short circuit to the bit lines, thus reducing the sensing delay, and rendering it practically insensitive to the bit-line capacitance. In addition, the virtual short circuit ensures equal bit-line voltages, thus eliminating the need for bit-line equalization during a read access.