Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
A Programmable Neural Measurement System for
Spikes and Local Field Potentials
Jonas Pistor, Janpeter Hoeffmann, Dagmar Peters-Drolshagen and Steffen Paul
Institute of Electrodynamics and Microelectronics (ITEM.me)
University of Bremen
Abstract- This paper presents a configurable system
measuring and pre-processing neurological data to be
transmitted over a wireless RF datalink (the datalink
itself is not part of this work). The system is capable of
measuring spikes and/or local field potentials of up to
128 electrodes with a variable resolution up to 16 Bit at
a variable sample rate up to 10 kHz consuming roughly
70mW. It represents the first step of the development of
an implantable neurological measurement unit. In this
paper the system-architecture, the digital system and the
FPGA implementation of the developed neural
measurement system are presented.
I. INTRODUCTION
Neural engineering represents a challenging part in
medical engineering. One major goal in neural engineering
is the development of an electrical interface to the human
brain. The motivation for this endeavor lies in the possible
cure of diseases like epilepsy, Parkinson and other
metabolic disorders in the brain. In addition the ongoing
research in neural prostheses relies on a proper
understanding of the brain functions.
To meet all the requirements of research and medical
facilities it is crucial to measure neurological data in longterm
and due to different applications with a highly flexible
amount of measured neurological data in terms of number
of channels and in terms of transmitted data rate.
A. Related Work
Groups at Brown University [1] and at Stanford
University [2] have both presented their systems to measure
neurological data. From the system point of view these two
systems differ in integration degree and in focus of
application.
The Wireless, Ultra Low Power, Broadband Neural
Recording Microsystem (NRM) developed at Brown
University is an implantable device designed for
transmitting cortical signals from 16 channels
percutaneously over a wireless data link. Since the system is
fully implantable it is necessary to incorporate a power and
data telemetry interacting with the external receiving
equipment. The NRM incorporates a two-panel system
approach. The power demanding parts of the NRM are
located in the cranial unit, whereas the sensing elements are
placed in the cortical unit. The two panels are connected
with a percranial cable.
The HermesD-System developed at Stanford University
is a measurement unit placed in skull-mounted aluminum
housing with the focus on a high data rate transmitted via
FSK over a relatively large distance.
Since the measurement unit should not be implanted, the
energy for the system can be provided by batteries. The
HermesD-System provides a high degree of flexibility in the
system architecture since the electrical components of the
measurement unit could easily be adapted or exchanged
during operation.
At the University of Utah [3], the INI-Chip was
developed. It is a highly integrated neural measurement
system, designed for a chronically cortical implant. This
single-chip device integrates all modules necessary for a
fully implantable neural measurement system.
B. This Work
The digital system presented in this paper aims to fit into
an intelligent neural measurement system, combining the
advantages of a fully implantable medical device with the
high flexibility of a skull-mounted external measurement
unit.
Since the hardware components of a fully implantable
device cannot be adapted or exchanged, the desired
flexibility has to come from a programmable electrical
device. The neuro frontend presented in this paper is
capable of measuring a dedicated subset or all of its up to
128 electrodes enabled by a user defined channel mask.
Besides the masking of channels, each channel is widely
adjustable in terms of resolution, sample rate and input filter
characteristics. All these adjustments can be done during
operation, leading only to small gaps in data acquisition.
The system provides a timestamp counter related to each
data packet, which serves as a quality indicator for the
signal integrity at all times.
Besides the high degree of configurability in terms of
collecting and handling highly parallel measurement data it
is crucial to meet the requirements of a possible (wireless)
RF Transceiver concerning the format of incoming
(neurological) data. The digital system described in this
paper is designed for a low power RF Transceiver (ZL70102
from Zarlink Semiconductor) expecting a serial SPI-data
stream which is divided into packets consisting of blocks
with a fixed number of bits to be sent out.
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