Design of a Fully Differential Current Mode Operational Amplifier with Improved Input-Output Impedances and Its Filter Applications

In this paper, a CMOS implementation of a fully differential current-mode operational amplifier (COA) is presented. To achieve very low input resistance, a new technique based on a positive feedback is used in the input transimpedance stage. Additionally, traditional current output stage (Arbel Goldminz output stage) with improved output resistance is selected as a transconductance stage. Results of simulations exhibit 96 dB DC gain, nearly 120Ω input, 30 MΩ output resistances and a gain-bandwidth product exceeding 90 MHz. The proposed COA is operated under ±1.5 V voltage supplies and designed with 0.35-μm CMOS process. Furthermore, COA-based 4 order band-pass (BP) filter consisting of Butterworth low-pass (LP) and high-pass (HP) filters is realized as an application example. SPICE simulation results are included to verify correctness of the designs.