A CMOS-realizable, compact and integrable all-pass structure and its tunable variant

Abstract

In this paper, two novel and compact structures of voltage-mode first-order all-pass filter are proposed. The first proposed structure is designed to provide non-inverting all-pass response only. It consists of only four MOS transistors and minimal number of passive elements i.e. one capacitor and one resistor. The proposed filter also offers the feature of high input impedance and is free from passive component matching constraints. Additionally, by including an inverting stage at the output, the first proposed design is extended to deliver both non-inverting and inverting all-pass responses simultaneously. Moreover, the proposed idea is further enriched with very essential feature of tunability by replacing the passive resistor with its active equivalent NMOS transistor. The theoretical analysis of the proposed design is verified with PSPICE simulation using TSMC 0.18 µm level-7 CMOS process parameters at supply voltage of ±0.9 V. Post layout verification is also explored to validate real time performance of proposed idea.