A Simple Macromodel Circuit for Operational Transconductance Amplifier with Low Frequency OTA-C Filter Application

This work presents an operational transconductance amplifier (OTA) macromodel for operation in low frequency OTA-C filters. The proposed macromodel is simple in structure, modeling characteristics similar to that of transistor-level based CMOS-OTA. The macromodel is based on a differential input balanced output OTA with finite input and output impedance. The development of the macromodel is based on four design stages providing input and output characteristics, limiting the range of operation controlled by limiting circuit of diodes, addition of non-linearity of the OTA using power series terms, and providing balanced output. The proposed macromodel design is tested in simulation of a fourth-order elliptic OTA-C filter, having macromodel based results compared to those based on transistor-level OTA using 90 nm CMOS technology in LTspice. The obtained simulation results reflect close agreement between those from macromodel and those of the transistor-level with reduction in computation time. Moreover, tuning of the filter for variable gain, bandwidth, and notch frequency is also tested using both the macromodel and CMOS-OTA.