Yong Ping Xu

Bio: Yong Ping Xu is an academic researcher from National University of Singapore. The author has contributed to research in topics: CMOS & Band-pass filter. The author has an hindex of 23, co-authored 97 publications receiving 1469 citations.

A Low-Power, High CMRR Neural Amplifier System Employing CMOS Inverter-Based OTAs With CMFB Through Supply Rails

Abstract: Multichannel neural amplifiers are commonly implemented with a shared reference whose input impedance is several times lower than that of the corresponding signal inputs. This huge impedance mismatch significantly degrades the total common mode rejection ratio (TCMRR) regardless of the amplifier’s intrinsic CMRR (ICMRR). This study reports a multichannel neural amplifier system that eliminates this impedance mismatch problem by using single-ended CMOS-inverter-based preamplifiers for both the reference and signal inputs. A common-mode feedback (CMFB) loop through the supply rails of the preamplifiers is implemented to enhance their ac input common mode range to $220\;\text{mV}_\text{pp}$ and their ICMRR to more than 90 dB at low frequencies. The ICMRR is maintained above 80 dB up to 1 kHz by minimizing the load drive mismatch between the signal and reference preamplifiers. Implemented in a CMOS 65 nm process, this 16-channel amplifier system operates at 1 V and consumes $118\; \upmu\text{W}$ . It has input referred noise of $4.13\; \upmu\text{V}_\text{rms}$ , leading to a noise efficiency factor (NEF) and a power efficiency factor (PEF) of 3.19 and 10.17, respectively. In vivo recordings of cortical neurons of a macaque were successfully acquired, demonstrating the ability of the amplifier to acquire neural signals in an unshielded environment.

A CMOS Continuous-Time Low-Pass Notch Filter for EEG Systems

Abstract: A CMOS OTA-C low-pass notch filter for EEG application is described. The pass-band covers four bands of brain wave and provides more than 65 dB attenuation for the 50 Hz power line interference. The OTA works in the weak inversion region and a low transconductance of 3 nA/V is achieved. The low transconductance enables using small capacitors in the OTA-C filter so that the filter is suitable for the multi-channel EEG integrated circuits. The measured results show the good performance of the filter for filtering the noise in acquired EEG signals.

A CMOS Carrier-less UWB Transceiver for WPAN Applications

Abstract: A carrier-less impulse-based UWB transceiver (TRX) chipset is presented. The TRX employs high-order pulse transmission with analog pulse-position modulation. Realized in a 0.18mum CMOS process, the TRX achieves a NF in the range of 7.7 to 8.1dB, an IIP3 of -12.3dBm, and a sensitivity of -80 to -72dBm. It consumes 76mW and 81 mW from a 1.8V supply in transmit and receive modes, respectively

A CMOS VGA With DC Offset Cancellation for Direct-Conversion Receivers

Abstract: A CMOS dB-linear variable gain amplifier (VGA) with a novel I/Q tuning loop for dc-offset cancellation is presented. The CMOS dB-linear VGA provides a variable gain of 60 dB while maintaining its 3-dB bandwidth greater than 2.5 MHz. A novel exponential circuit is proposed to obtain the dB-linear gain control characteristics. Nonideal effects on dB linearity are analyzed and the methods for improvement are suggested. A varying-bandwidth LPF is employed to achieve fast settling. The chip is fabricated in a 0.35-mum CMOS technology and the measurement results demonstrate the good dB linearity of the proposed VGA and show that the tuning loop can effectively remove dc offset and suppress I/Q mismatch effects simultaneously.

A Compact, Low Input Capacitance Neural Recording Amplifier

Abstract: Conventional capacitively coupled neural recording amplifiers often present a large input load capacitance to the neural signal source and hence take up large circuit area. They suffer due to the unavoidable trade-off between the input capacitance and chip area versus the amplifier gain. In this work, this trade-off is relaxed by replacing the single feedback capacitor with a clamped T-capacitor network. With this simple modification, the proposed amplifier can achieve the same mid-band gain with less input capacitance, resulting in a higher input impedance and a smaller silicon area. Prototype neural recording amplifiers based on this proposal were fabricated in 0.35 μm CMOS, and their performance is reported. The amplifiers occupy smaller area and have lower input loading capacitance compared to conventional neural amplifiers. One of the proposed amplifiers occupies merely 0.056 mm2. It achieves 38.1-dB mid-band gain with 1.6 pF input capacitance, and hence has an effective feedback capacitance of 20 fF. Consuming 6 μW, it has an input referred noise of 13.3 μVrms over 8.5 kHz bandwidth and NEF of 7.87. In-vivo recordings from animal experiments are also demonstrated.

A 2 $\mu\hbox{W}$ 100 nV/rtHz Chopper-Stabilized Instrumentation Amplifier for Chronic Measurement of Neural Field Potentials

Abstract: This paper describes a prototype micropower instrumentation amplifier intended for chronic sensing of neural field potentials (NFPs). NFPs represent the ensemble activity of thousands of neurons and code-useful information for both normal activity and disease states. NFPs are small - of the order of tens of muV- and reside at low bandwidths that make them susceptible to excess noise. Therefore, to ensure the highest fidelity of signal measurement for diagnostic analysis, the amplifier is chopper-stabilized to eliminate 1/f and popcorn noise. The circuit was prototyped in an 0.8 mum CMOS process and consumes under 2.0 muW from a 1.8 V supply. A noise floor of 0.98 muVrms was achieved over a bandwidth from 0.05 to 100 Hz; the noise-efficiency factor of 4.6 is one of the lowest published to date. A flexible on-chip high-pass filter is used to suppress front-end electrode offsets while maintaining relevant physiological data. The monolithic architect and micropower low-noise low-supply operation could help enable applications ranging from neuroprosthetics to seizure monitors that require a small form factor and battery operation. Although the focus of this paper is on neurophysiological sensing, the circuit architecture can be applied generally to micropower sensor interfaces that benefit from chopper stabilization.

A review of MEMS oscillators for frequency reference and timing applications

Abstract: MEMS-based oscillators are an emerging class of highly miniaturized, batch manufacturable timing devices that can rival the electrical performance of well-established quartz-based oscillators. In this review, a description is given of the key properties of a MEMS resonator that determine the overall performance of a MEMS oscillator. Piezoelectric, capacitive and active resonator transduction methods are compared and their impact on oscillator noise and power dissipation is explained. An overview is given of the performance of MEMS resonators and MEMS-based oscillators that have been demonstrated to date. Mechanisms that affect the frequency stability of the resonator, such as temperature-induced frequency drift, are explained and an overview is given of methods that have been demonstrated to improve the frequency stability. The aforementioned performance indicators of MEMS-based oscillators are benchmarked against established quartz and CMOS technologies.

A 1-V 450-nW Fully Integrated Programmable Biomedical Sensor Interface Chip

Abstract: This paper presents a fully integrated programmable biomedical sensor interface chip dedicated to the processing of various types of biomedical signals. The chip, optimized for high power efficiency, contains a low noise amplifier, a tunable bandpass filter, a programmable gain stage, and a successive approximation register analog-to-digital converter. A novel balanced tunable pseudo-resistor is proposed to achieve low signal distortion and high dynamic range under low voltage operations. A 53 nW, 30 kHz relaxation oscillator is included on-chip for low power consumption and full integration. The design was fabricated in a 0.35 mum standard CMOS process and tested at 1 V supply. The analog front-end has measured frequency response from 4.5 mHz to 292 Hz, programmable gains from 45.6 dB to 60 dB, input referred noise of 2.5 muVrms in the amplifier bandwidth, a noise efficiency factor (NEF) of 3.26, and a low distortion of less than 0.6% with full voltage swing at the ADC input. The system consumes 445 nA in the 31 Hz narrowband mode for heart rate detection and 895 nA in the 292 Hz wideband mode for ECG recording.

Medical Instrumentation Application And Design

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Wireless body sensor networks based on metamaterial textiles

Abstract: Wireless networks of sensors, displays and smart devices that can be placed on a person’s body could have applications in health monitoring, medical interventions and human–machine interfaces. Such wireless body networks are, however, typically energy-inefficient and vulnerable to eavesdropping because they rely on radio-wave communications. Here, we report energy-efficient and secure wireless body sensor networks that are interconnected through radio surface plasmons propagating on metamaterial textiles. The approach uses clothing made from conductive fabrics that can support surface-plasmon-like modes at radio communication frequencies. Our body sensor networks enhance transmission efficiencies by three orders of magnitude compared to conventional radiative networks without the metamaterial textile, and confine wireless communication to within 10 cm of the body. We also show that the approach can offer wireless power transfer that is robust to motion and textile-based wireless touch sensing. Energy-efficient and secure wireless body sensor networks can be created by using conductive fabrics that support surface-plasmon-like modes at radio communication frequencies.