Area-efficient layout design for CMOS output transistors

A novel layout design to effectively reduce the layout area of the thin-oxide NMOS and PMOS devices in CMOS output buffers with ESD consideration is proposed. With respect to the traditional finger-type layout, the large-dimension output NMOS and PMOS devices are realized by multiple octagonal cells. Without using extra ESD-optimization process, the output NMOS and PMOS devices in this octagon-type layout can provide higher driving/sinking current and better ESD robustness within smaller layout area. The drain-to-bulk parasitic capacitance at the output node is also reduced by this octagon-type layout. Experimental results in a 0.6-μm CMOS process have shown that the output driving (sinking) current of CMOS output buffers in per unit layout area is increased 47.7% (34.3%) by this octagon-type layout. The HBM (MM) ESD robustness of this octagon-type output buffer in per unit layout area is also increased 41.5% (84.6%), as comparing to the traditional finger-type output buffer. This octagon-type layout design makes a substantial contribution to the submicron or deep-submicron CMOS IC's in high-density and high-speed applications.