A high bandwidth constant g(m) and slew-rate rail-to-rail CMOS input circuit and its application to analog cells for low voltage VLSI systems

A new rail-to-rail CMOS input architecture is presented that delivers behavior nearly independent of the common-mode level in terms of both transconductance and slewing characteristics, Feedforward is used to achieve high common-mode bandwidth, and operation does not rely on analytic square law characteristics, making the technique applicable to deep submicron technologies. From the basis of a transconductor design, an asynchronous comparator and a video bandwidth op-amp are also developed, providing a family of general purpose analog circuit functions which may be used in high (and low) bandwidth mixed-signal systems, Benefits for the system designer are that the need for rigorous control of common-mode levels is avoided and input signal swings right across the power supply range can be easily handled, A further benefit is that having very consistent performance, the circuits can be easily described in VHDL (or other behavioral language) to allow simulation of large mixed-signal systems. The circuits presented may be easily adapted for a range of requirements, Results are presented for representative transconductor, op-amp, and comparator designs fabricated in a 0.5-mu m 3.3-V digital CMOS process.