A Digital-Based Ultra-Low-Voltage Pseudo-Differential CMOS Schmitt Trigger

Abstract

A digital-based Pseudo-differential Schmitt trigger is proposed in this paper which is suitable for ultra-low voltages and pure digital integrated circuit technologies. The proposed Schmitt trigger is implemented according to the design procedure of an analog Schmitt trigger and only using digital CMOS inverters. It is composed of a differential comparator consisting of two CMOS inverters and a cross-coupled inverter pair positive feedback which has simultaneously two outputs of noninverting and inverting. The proposed circuit is the only digital Schmitt trigger which operates in differential mode and its hysteresis center can be changed by the input voltage. Implementing the circuit in digital-based allows the proposed Schmitt trigger to operate in 0.4[Formula: see text]V ultra-low-voltage. Principle operation of the proposed circuit is discussed theoretically and using formulas and its performance is verified by simulation in TSMC 0.18[Formula: see text][Formula: see text]m CMOS process. The proposed circuit occupies only [Formula: see text][Formula: see text][Formula: see text]m2 chip area due to the very low number of transistors. The hysteresis width of the proposed Schmitt trigger is 205[Formula: see text]mV and consumes only 6.64[Formula: see text]nW power.