School of Electrical and Computer Engineering
Text Box: Multichannel Wireless Neural Recording System Text Box: Wireless recording of the neural signals from a large number of recording sites is highly desired because a growing number of neuroscientists have become interested in visualizing the extracellular activities of hundreds to thousands of single neurons in awake, freely moving animals. High site-count neural recording systems are currently hardwired and the tethering effects of the wires attached to implanted electrodes interfere with natural animal behavior and bias the experimental outcomes. Considering that neural signals have a bandwidth of ~10 kHz, a wideband telemetry link in the order of tens of MHz is needed to wirelessly record from a large number of sites, simultaneously, without loosing any information. So far most of the reported wireless neural recording systems have been battery powered, and therefore, not fully implantable except for a short period of time. The objective of the present research is to develop an inductively powered >100 channel wireless implantable neural recording system for long-term in vivo experiments. Text Box: 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. Text Box: 15-Ch WINeR-3 ASIC: A 3 mm ื 3 mm 15-channel wireless neural recording system on a chip (SoC) implemented in AMI-0.5 um standard CMOS process. Text Box: 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. Text Box: Related Publications: H.M. Lee and M. Ghovanloo, “An integrated power-efficient active rectifier with offset-controlled high speed comparators for inductively-powered applications,” IEEE Trans. on Circuits and Systems I, vol. 58, no. 8, pp. 1749-1760, Aug. 2011. M. Yin and M. Ghovanloo, “A low-noise clockless simultaneous 32-channel wireless neural recording system with adjustable resolution,” Analog Integrated Circuits and Signal Processing, vol. 66, no. 3, pp. 417-431, March 2011. S.B. Lee, H.M. Lee, M. Kiani, U. Jow, and M. Ghovanloo, “An inductively powered scalable 32-channel wireless neural recording system-on-a-chip for neuroscience applications,” IEEE Trans. on Biomed. Circuits and Systems, vol. 4, no. 6, pp. 360-371, Dec. 2010. M. Kiani and M. Ghovanloo, “An RFID-based closed loop wireless power transmission system for biomedical applications,” IEEE Trans. on Circuits and Systems II, vol. 57, no. 4, pp. 260-264, Apr. 2010. 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. Text Box: 2-Ch Wireless WINeR-1 ASIC: A 2.2 mm ื 2.2 mm 2-channel wireless neural recording system on a chip (SoC) implemented in AMI-1.5 um standard CMOS process.

ฉ 2012 Maysam Ghovanloo
Text Box: 32-Ch Clockless WINeR-5 ASIC: A 3.3 mm ื 3 mm 32-channel wireless neural recording system on a chip (SoC) with no running clock implemented in AMI-0.5 um standard CMOS process. Text Box: 32-Ch Inductively Powered WINeR-6 ASIC: A 4.9 mm ื 3.3 mm 32-channel wireless neural recording system on a chip (SoC) with high efficiency rectifier and low dropout regulator blocks for closed-loop inductive powering implemented in AMI-0.5 um standard CMOS process. Text Box: By adding a highly efficient fully-integrated power management block (PMIC) to the WINeR-6 SoC we have been able to power up the entire 32-channel wireless neural recording system wirelessly while substituting the bulky batteries with a much lighter coil. The key advantages of the new inductively-powered WINeR-6 system is that unlike previous wireless neural recording systems it can run indefinitely without requiring the animal subject to carry around a large payload of batteries. Instead, the headstage can be equipped with more sensors, recording channels, data acquisition, and conditioning circuitry. Our state-of-the-art closed-loop power transmission system can actively compensate for the coil misalignments that result from the animal movements and maintain the received power constant at a level that is just enough to operate the WINeR-6 headstage.