Circuitry for a wireless microsystem for neural recording microprobes

Abstract

Abstract-Integrated circuits for use in a wireless microsystem used in neural recording is described. The implantable microsystem will be powered and transmit digitized data using RF telemetry. Recorded neural signals are amplified, multiplexed, digitized using a 2 nd order sigma-delta modulator, and then transmitted to the outside world by an on-chip transmitter. The circuit is designed using a standard 1.5µm CMOS process. Several circuit blocks have been desgigned, fabricated and show to operate as expected. Keywords -Telemetry, Microsystem, Sigma-delta, Microprobe I. INTRODUCTIONDirect recording of neural activity has been longed for by physiologists and scientists in order to unveil the secrets of biological neural networks, which may inspire the innovations in artificial intelligence, human physiology and biomedical prosthesis.The silicon micromachined microelectrode developed at the University of Michigan is one of the successful approaches to record the neural signals from the central and peripheral nerve systems [1]-[3,] and some efforts have been made to accomplish the above goal [4]- [6]. A low-power, wireless prototype of an integrated circuit chip is being developed for an implantable multichannel recording microprobe for central nervous system. The integrated circuit chip is powered using RF telemetry by an external coil that is separated from the receiver coil by a distance of several millimeters. The chip allows recording of ±500 µV neural signals from axons regenerated through a micromachined silicon sieve electrode. These signals are amplified using pre-amplifiers, multiplexed, digitized with a 10-bit sigma-delta modulator, and then transmitted to the outside world using an on-chip transmitter. The circuit is designed using a standard 1.5µm CMOS process. It is obvious that inductive RF power delivery and data transmission are desired in the design of the implanted recording microsystem to reduce potential hazards of interconnect wires and batteries to tissues in chronic recording applications. One of the main challenges of the required system is to transfer sufficient power to the implant and produce clean power supply needed for high-resolution recording and conversion to digital format of the recorded data.II. SYSTEM OVERVIEW The IC block diagram, shown in Fig. 1, illustrates the operation of the telemetry system.A. Front-end circuitry The front-end circuitry includes circuit blocks of voltage regulators, clock recovery, ASK demodulator, power-onreset and RF limiter [7,8].The front-end circuitry receives power and commands from the external transmitter so as to keep the implanted chip functional. It also recovers clock and reset signals for digital blocks as well as protect the on-chip electronics from high RF voltage. However, RF power delivery may introduce high power supply noise to the implanted chip, which may be much higher than 0.1% required by 10 bit resolution. In order to achieve the high resolution, over-sampling method is chosen to implement the ADC [9,10]. In this application, a s...

An implantable bi-directional wireless transmission system for transcutaneous biological signal recording

“…the firing intervals from the neural signal, rather than transmitting the raw signal in its entirety (Akin et al 1998, Donaldson et al 2003 are impractical in certain regards. Recent research increasingly requires the raw signal, and particularly the high-frequency neural signal, to be recorded and acquired while the animal is conscious and with minimal constraint (Yu and Najafi 2001).…”