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.
- S.B. Lee, H.M. Lee, M. Kiani, U.M. Jow, and M. Ghovanloo, “An Inductively Powered Scalable 32-ch Wireless Neural Recording System-on-a-Chip with Power Scheduling for Neuroscience Applications,” Digest of technical papers IEEE Intl. Solid State Cir. Conf., pp. 120-121, Feb. 2010.
- M. Yin and M. Ghovanloo, "Using pulse width modulation for wireless transmission of neural signals in multichannel neural recording systems," IEEE Trans. on Neural Sys. Rehab. Eng., vol. 17, no. 4, pp. 354-363, Aug. 2009.
- M. Yin, S.B. Lee, and M. Ghovanloo, "In vivo testing of a low noise 32-channel wireless neural recording system," Proc. IEEE 31st Eng. in Med. and Biol. Conf., pp. 1608-1611, Sep. 2009.
- M. Yin and M. Ghovanloo, "A flexible 32-channel simultaneous wireless neural recording system with adjustable resolution", Digest of technical papers IEEE Intl. Solid State Cir. Conf., pp. 432-433, Feb. 2009.
- M. Yin and M. Ghovanloo, "A low-noise receiver for multichannel wireless neural recording," Proc. IEEE 30th Eng. in Med. and Biol. Conf., pp. 4222-4225, Aug. 2008.
- M. Yin and M. Ghovanloo, "A wideband PWM-FSK receiver for wireless implantable neural recording applications," Proc. IEEE Intl. Symp. on Circuits and Systems, pp. 1556-1559, May 2008.
- M. Yin and M. Ghovanloo, "A clockless ultra low-noise low-power wireless implantable neural recording system," Proc. IEEE Intl. Symp. on Circuits and Systems, pp. 1756-1759, May 2008.
- M. Yin and M. Ghovanloo, "Wideband Flexible Transmitter and Receiver Pair for Multi-channel Wireless Neural Recording Applications," IEEE-MWSCAS 2007 IEEE-NEWCAS 2007, pp. 85–88,Aug 2007.
- M. Yin and M. Ghovanloo, "A low-noise preamplifier with adjustable gain and bandwidth for biopotential recording applications," IEEE International Symposium on Circuits and Systems (ISCAS), pp.321–324, May 2007.
- M. Yin and M. Ghovanloo, "Using Pulse Width Modulation for Wireless Transmission of Neural Signals in a Multi-channel Neural Recording System," IEEE International Symposium on Circuits and Systems (ISCAS), pp.3127–3130, May 2007.
- M. Yin, R.M. Field, and M. Ghovanloo, "A 15-channel wireless neural recording system based on time division multiplexing of pulse width modulated signals," IEEE-EMBS Special Topic Conf. on Microtechnologies in Med. and Biol., pp. 221-224, May 2006.