March 2017

Byunghun successfully defended his thesis and graduated from GT-Bionics as a PhD student. Congratulations, Dr. Byunghun Lee!

Congratulation to Daniel Canales for receiving the ECE Undergraduate Research Award!

Jaemyung successfully defended his thesis and graduated from GT-Bionics as a PhD student. Congratulations, Dr. Jaemyung Lim!

February 2017

Dr. Ghovanloo has been awarded promotion to Full Professor. Congratulations! Please see the story here.

September 2016

GT just released story about our EnerCage project!

Dr. Ghovanloo will give a talk on 8th Seminar on Electronics and Advanced Design with title "Implantable and wearable microelectronic device to improve quality of life for people with disabilities".

August 2016

We have two papers at EMBC'16.

Temi successfully defended her thesis and graduated from GT-Bionics as a PhD student. Congratulations, Dr. Temi Prioleau!

June 2016

Temi received Chi Foundation award. Congratulations Temi!

Low-Power Head-Mounted
Deep Brain Stimulator

This project seeks to develop wireless circuit interface and associated electronics for an implantable neural stimulating microsystem with a large number of stimulating sites for use in neural prostheses. The implantable microsystem should be inductively powered, button-sized, with 1024 sites, arranged in a 3-D configuration, with 128 simultaneous channels, each capable of sourcing ±100mA. The major challenges towards this goal are the implant size, microassembly method, large number of sites, effective and safe stimulation, low power consumption, and wideband wireless link between the implant and the external world.

The electrical connection to the neural tissue is formed through either a group of metal microwire electrodes or a micromachined silicon microelectrode array. For every recording channel, a low-noise low-power amplifier (LNA), which is capable of amplifying signals from mHz to kHz range, is used to amplify the acquired neural signals. A capacitive highpass filter at the input of every LNA rejects the large DC offset generated at the electrode-tissue interface but not the low-frequency evoked potentials that may contain significant neural information. 32 identical neural recording channels plus 4 monitoring channels that marks the beginning of each frame are multiplexed by a 36 to 1 multiplexer that is controlled by circular shift register (SHR). The SHR is run at 720 kHz by a triangular waveform generator, taking 20k samples/sec from every channel. This sampling rate should be enough for reconstruction of the neural signals which have a bandwidth of 8~10 kHz. A sample and hold (S&H) circuit follows the TDM to stabilize the acquired samples before pulse width modulation (PWM). The PWM is dedicated to convert the analog signal at the output of the S&H to a pseudo-digital signal that is more robust against noise. Using a pulse width modulator instead of an analog to digital converter (ADC) results in less power consumption, easier synchronization, and less complexity in the implantable device.

A voltage controlled oscillator (VCO) converts the PWM signal to a frequency shift keyed (FSK) carrier in the industrial, scientific, and medical (ISM) band. Due to the short range application of the system (within the animal cage), the VCO output can be directly applied to a miniature patch antenna with a proper off-chip matching circuit. A custom-designed ISM-band receiver is used as the external part of the system. The received PWM signal is directly converted to digitized samples using Time-to-Digital Conversion (TDC) technique on an FPGA, and transferred to a PC through USB. Finally by demultiplexing the TDM samples, the original neural signals are reconstructed. The wireless neural recording system also contains a receiver coil followed by an on-chip rectifier, filter, and regulator that provide the rest of the implant with a clean DC supply. The power carrier frequency is selected to have minimum interference with the neural signals and ISM carrier.

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