A closed-loop deep brain stimulation device with a logarithmic pipeline ADC

This dissertation is a summary of the research on integrated closed-loop deep brain stimulation for treatment of Parkinson's disease. Parkinson's disease is a progressive disorder of the central nervous system affecting more than three million people in the United States. Deep Brain Stimulation (DBS) is one of the most effective treatments of Parkinson symptoms. DBS excites the Subthalamic Nucleus (STN) with a high frequency electrical signal. The proposed device is a single-chip closed-loop DBS system. Closed-loop feedback of sensed neural activity promises better control and optimization of stimulation parameters than with open-loop devices.;Thanks to a novel architecture, the prototype system incorporates more functionality yet consumes less power and area compared to other systems. Eight front-end low-noise neural amplifiers (LNAs) are multiplexed to a single high-dynamic-range logarithmic, pipeline analog-to-digital converter (ADC). To save area and power consumption, a high dynamic-range log ADC is used, making analog automatic gain control unnecessary. The redundant 1.5b architecture relaxes the requirements for the comparator accuracy and comparator reference voltage accuracy. Instead of an analog filter, an on-chip digital filter separates the low frequency neural field potential signal from the neural spike energy. An on-chip controller generates stimulation patterns to control the 64 on-chip current-steering DACs. The 64 DACs are formed as a cascade of a single shared 2-bit coarse current DAC and 64 individual bi-directional 4-bit fine DACs. The coarse/fine configuration saves die area since the MSB devices tend to be large.;A prototype device is fabricated in 0.18 mum CMOS with a MiM capacitor option and occupies 2.67 mm2. The total power consumption of the entire system, including neural amplifiers, log ADC, current DAC, controller and digital filters, reference generation, clock generation and biasing, is 112 muW in normal operation mode and 351 muW in configuration mode, which is significantly less than that of state-of-the-art stimulator circuits.;Real-time neural activity was recorded with the prototype device connected to microprobes that are chronically implanted in two Long Evans rats. The recorded in-vivo signal clearly shows neural spikes of 10.2 dB signal-to-noise ratio (SNR) as well as a periodic artifact from neural stimulation. The recorded neural information has been analyzed with single unit sorting and principal component analysis (PCA). The PCA scattering plots from multi-layers of cortex represent diverse information from either single or multiple neural sources. This exploits the benefits of a three-dimensional multi-layer neural probe such as Michigan probe. The single-unit neural sorting analysis along with PCA verifies the feasibility of the implantable CDBS device as an application to in-vivo neural recording interface. To program an optimal closed-loop algorithm, further intensive studies will be necessary to examine the neural pattern changes related to the CDBS treatment. In addition, the CDBS device and implantable brain-machine interface (BMI) unit, has potential for the treatment of other neurological disorders such as stroke, epilepsy and seizure.