Projeto de um filtro Gm-C aplicado a neuroestimuladores utilizando uma nova topologia de transcondutor

Abstract

This graduation project presents the design of a filter Gm-C applied to stimulation systems, particularly in the measurement of residual charges. The filter proposal is based on using a new concept of transcondutor called RCT - Reverse Cascode Transconductor. In turn, the transconductor allows the realization of ultra-low tranconductances (pA/V), allowing large time constants than be realized using capacitors range in sub-picoFarads. The concept is demonstrated by characterizing the transconductor at the simulation level. A 0.7pA/V was simulated to demonstrate the application of a Butterworth low-pass filter of the second order with cutoff frequency of 8mHz. The innovation of this design is non-conventional use of classic telescopic cascode topology, where the voltage signal is applied to the terminal that would a usually be used as output. Thus, with the high impedance provided by this topology, the conversion of the input voltage into a femto-Ampere signal is greatly simplified. The great potential of RCT in relation to the other topologies in the literature is the dispensability of complex techniques for transconductance reduction obtained naturally in this circuit. The final design is demonstrated with its target application, monitoring DC component in stimulation currents and at residual voltages across electrodes. Simulated results suggests a great potential for the application of RCT to implantable stimulation systems, but also in fields of knowledge where large time constants are required. The circuit was proposed using the UMC 130nm CMOS process technology, however, due to its simplicity of implementation may easily be designed for other technologies.