Advances in Technologies for Implantable Bioelectronics
This chapter focuses on the implantable readout module, which provides the direct interface with the biological tissues and is strongly dependent on the type of biosignal. It introduces implantable readout circuits for biopotential and electrochemical sensing. The chapter presents the state-of-the-art analog-to-digital converter (ADC) architectures for implantable readouts. It also introduces a test-case ADC for neural recording applications. The chapter covers the powering issues and challenges. It provides the possible solutions for self-powered implantable biosensors. The implantable readout circuits extract information from a variety of biosensors within the human body, providing the interface between biosignals and digital signal processor. The readout circuits for electrochemical biosensors process the output currents from three-electrode transducers. Most of the circuit implementations transform the current signal to a voltage signal by using a transimpedance amplifier. There are two common approaches to process biopotential signals, based on either a medium-resolution Nyquist ADC, such as a successive approximation register, or a high-resolution oversampling ADC, such as a Sigma-Delta modulator.