Novel Schmitt Trigger and Square-Wave Generator Using Single Current Amplifier

Abstract

This paper presents an important missing building block for mixed-mode signal processing: a Schmitt trigger circuit based on the current amplifier. Schmitt trigger is used extensively in both the analogue and digital areas. The transfer characteristics of the proposed design are independent on the supply voltage. Unlike Schmitt triggers incorporating other types of amplifiers, the proposed design is totally active. It does not require passive resistors and hence it shall be more attractive for VLSI implementation. The proposed circuit is utilized to implement a novel current mode square-wave oscillator using a single current amplifier that provides differential current signals. The output amplitude can be controlled without additional circuitry. Current generators are particularly essential for bio-impedance measurement. Comparison with their counterparts using the operational amplifier, transconductance operational amplifier, transresistance operational amplifier, and current conveyor demonstrates several advantageous features of the proposed circuits. The experimental results obtained from primary prototypes fabricated using standard 150 nm CMOS process are provided. It is shown that the proposed Schmitt trigger and the square wave generator nominally consume $8~\mu \text{W}$ and $11~\mu \text{W}$ while working in the MHz range.