C.T. Charles

Bio: C.T. Charles is an academic researcher from University of Utah. The author has contributed to research in topics: CMOS & Phase detector. The author has an hindex of 9, co-authored 20 publications receiving 1656 citations. Previous affiliations of C.T. Charles include University of Washington & Seattle University.

A low-power low-noise CMOS amplifier for neural recording applications

Abstract: There is a need among scientists and clinicians for low-noise low-power biosignal amplifiers capable of amplifying signals in the millihertz-to-kilohertz range while rejecting large dc offsets generated at the electrode-tissue interface. The advent of fully implantable multielectrode arrays has created the need for fully integrated micropower amplifiers. We designed and tested a novel bioamplifier that uses a MOS-bipolar pseudoresistor element to amplify low-frequency signals down to the millihertz range while rejecting large dc offsets. We derive the theoretical noise-power tradeoff limit - the noise efficiency factor - for this amplifier and demonstrate that our VLSI implementation approaches this limit by selectively operating MOS transistors in either weak or strong inversion. The resulting amplifier, built in a standard 1.5-/spl mu/m CMOS process, passes signals from 0.025Hz to 7.2 kHz with an input-referred noise of 2.2 /spl mu/Vrms and a power dissipation of 80 /spl mu/W while consuming 0.16 mm/sup 2/ of chip area. Our design technique was also used to develop an electroencephalogram amplifier having a bandwidth of 30 Hz and a power dissipation of 0.9 /spl mu/W while maintaining a similar noise-power tradeoff.

A Calibrated Phase/Frequency Detector for Reference Spur Reduction in Charge-Pump PLLs

Abstract: This brief presents a new technique for minimizing reference spurs in a charge-pump phase-locked loop (PLL) while maintaining dead-zone-free operation. The proposed circuitry uses a phase/frequency detector with a variable delay element in its reset path, with the delay length controlled by feedback from the charge-pump. Simulations have been performed with several PLLs to compare the proposed circuitry with previously reported techniques. The proposed approach shows improvements over previously reported techniques of 12 and 16 dB in the two closest reference spurs

Wireless Data Links for Biomedical Implants: Current Research and Future Directions

Abstract: This paper outlines the requirements for high-rate implantable data links as would be used in applications such as visual prostheses. Methods used in current research are categorized and recently reported implementations are discussed and compared. The most significant shortcoming of current implementations is in their data rates which are limited to several Mb/s, while rates of several tens of Mb/s are envisioned to be necessary for a functional visual prosthesis. Several promising methods for achieving increased data rates are discussed, including ultra-wide band signaling, infrared transmission, and body conduction techniques.

Low-power UWB pulse generators for biomedical implants

Abstract: Four low-power ultra-wide band (UWB) pulse generators for biomedical implants are investigated in this paper. The designs presented have no static power dissipation and start-up times in the neighborhood of 200 ps. All four designs were simulated and three were also fabricated in a modern 65 nm CMOS process. Measured data is also presented. The designs were evaluated for the best performance in a low-power UWB transmitter employing pulse-position modulation.

A low-power 3.1–5GHz ultra-wideband low noise amplifier utilizing Miller Effect

Abstract: The candidate topologies for low-power, wideband LNAs are analyzed in this paper, and a novel LNA topology for the 3.1–5 GHz UWB frequency band is presented. The LNA uses subthreshold biasing and employs its Miller capacitance as part of a Butterworth-type bandpass filter for input impedance matching. The LNA achieves a power gain of 14.4 dB with S 11 less than −10 dB across the 3.1–5 GHz frequency band. The power consumption is less than 1.5 mW, and the noise figure varies from 5.7–6.3 dB across the 3.1–5 GHz frequency band.

A Low-Power Integrated Circuit for a Wireless 100-Electrode Neural Recording System

Abstract: Recent work in field of neuroprosthetics has demonstrated that by observing the simultaneous activity of many neurons in specific regions of the brain, it is possible to produce control signals that allow animals or humans to drive cursors or prosthetic limbs directly through thoughts. As neuroprosthetic devices transition from experimental to clinical use, there is a need for fully-implantable amplification and telemetry electronics in close proximity to the recording sites. To address these needs, we developed a prototype integrated circuit for wireless neural recording from a 100-channel microelectrode array. The design of both the system-level architecture and the individual circuits were driven by severe power constraints for small implantable devices; chronically heating tissue by only a few degrees Celsius leads to cell death. Due to the high data rate produced by 100 neural signals, the system must perform data reduction as well. We use a combination of a low-power ADC and an array of "spike detectors" to reduce the transmitted data rate while preserving critical information. The complete system receives power and commands (at 6.5 kb/s) wirelessly over a 2.64-MHz inductive link and transmits neural data back at a data rate of 330 kb/s using a fully-integrated 433-MHz FSK transmitter. The 4.7times5.9 mm2 chip was fabricated in a 0.5-mum 3M2P CMOS process and consumes 13.5 mW of power. While cross-chip interference limits performance in single-chip operation, a two-chip system was used to record neural signals from a Utah Electrode Array in cat cortex and transmit the digitized signals wirelessly to a receiver

Response to FCC 98-208 notice of inquiry in the matter of revision of part 15 of the commission's rules regarding ultra-wideband transmission systems

Abstract: In general, Micropower Impulse Radar (MIR) depends on Ultra-Wideband (UWB) transmission systems. UWB technology can supply innovative new systems and products that have an obvious value for radar and communications uses. Important applications include bridge-deck inspection systems, ground penetrating radar, mine detection, and precise distance resolution for such things as liquid level measurement. Most of these UWB inspection and measurement methods have some unique qualities, which need to be pursued. Therefore, in considering changes to Part 15 the FCC needs to take into account the unique features of UWB technology. MIR is applicable to two general types of UWB systems: radar systems and communications systems. Currently LLNL and its licensees are focusing on radar or radar type systems. LLNL is evaluating MIR for specialized communication systems. MIR is a relatively low power technology. Therefore, MIR systems seem to have a low potential for causing harmful interference to other users of the spectrum since the transmitted signal is spread over a wide bandwidth, which results in a relatively low spectral power density.

System and method for waking an implantable medical device from a sleep state

Abstract: A system and method for waking up a satellite implantable medical device ('IMD') from a sleep state in which power consumption by the satellite IMD is essentially zero. The satellite IMD may be adapted to perform one or more designated measurement and/or therapeutic functions. The satellite IMD includes a wake-up sensor that is adapted to sense the presence or absence of a wake-up field generated by a primary IMD or an external device. The wake-up field may be an electromagnetic field, a magnetic field, or a physiologically sub-threshold excitation current (i.e., E-field). Upon sensing by the wake-up sensor of the wake-up field, other components of the satellite IMD, which may include a controller, a sensing and/or therapy module, and/or a communications module, are awakened to perform one or more designated functions.

A low-power, low-noise CMOS amplifier for neural recording applications

Abstract: There is a need among scientists and clinicians for low-noise, low-power biosignal amplifiers capable of amplifying signals in the mHz to kHz range while rejecting large dc offsets generated at the electrode-tissue interface. The advent of fully-implantable multielectrode arrays has created the need for fully-integrated micropower amplifiers. We designed and tested a novel bioamplifier that uses a MOS-bipolar pseudo-resistor to amplify signals down to the mHz range while rejecting large dc offsets. We derive the theoretical noise-power tradeoff limit - the noise efficiency factor - for this amplifier and demonstrate that our VLSI implementation approaches that limit. The resulting amplifier, built in a standard 1.5/spl mu/m CMOS process, passes signals from 0.1mHz to 7.2kHz with an input-referred noise of 2.2/spl mu/Vrms and a power dissipation of 80/spl mu/W while consuming 0.16mm/sup 2/ of chip area.

An Energy-Efficient Micropower Neural Recording Amplifier

Abstract: This paper describes an ultralow-power neural recording amplifier. The amplifier appears to be the lowest power and most energy-efficient neural recording amplifier reported to date. We describe low-noise design techniques that help the neural amplifier achieve input-referred noise that is near the theoretical limit of any amplifier using a differential pair as an input stage. Since neural amplifiers must include differential input pairs in practice to allow robust rejection of common-mode and power supply noise, our design appears to be near the optimum allowed by theory. The bandwidth of the amplifier can be adjusted for recording either neural spikes or local field potentials (LFPs). When configured for recording neural spikes, the amplifier yielded a midband gain of 40.8 dB and a -3-dB bandwidth from 45 Hz to 5.32 kHz; the amplifier's input-referred noise was measured to be 3.06 muVrms while consuming 7.56 muW of power from a 2.8-V supply corresponding to a noise efficiency factor (NEF) of 2.67 with the theoretical limit being 2.02. When configured for recording LFPs, the amplifier achieved a midband gain of 40.9 dB and a -3-dB bandwidth from 392 mHz to 295 Hz; the input-referred noise was 1.66 muVrms while consuming 2.08 muW from a 2.8-V supply corresponding to an NEF of 3.21. The amplifier was fabricated in AMI's 0.5-mum CMOS process and occupies 0.16 mm2 of chip area. We obtained successful recordings of action potentials from the robust nucleus of the arcopallium (RA) of an anesthesized zebra finch brain with the amplifier. Our experimental measurements of the amplifier's performance including its noise were in good accord with theory and circuit simulations.