A low-noise clockless simultaneous 32-channel wireless neural recording system with adjustable resolution

Abstract

We present a 32-channel wireless implantable neural recording (WINeR-5) system-on-a-chip (SoC) that operates based on time division multiplexing (TDM) of pulse width modulated (PWM) samples, similar to a singleslope analog to digital converter (ADC) that is made wireless. By transmitting a TDM-PWM signal, we have relaxed the need for wide bandwidth and accurate timing between transmitter and receiver units, which is necessary in wideband digital wireless links. The WINeR-5 system uses FSK modulation scheme with RF carrier at 898/ 926 MHz. The baseband TDM-PWM signal bandwidth is 18 MHz, which is also the bandwidth of the receiver baseband low-pass filter. Further, by moving the digitization circuitry outside the body, we have reduced the size, complexity, and power consumption of the implantable unit. A clockless asynchronous design has been utilized to manage TDM switching times such that no switching occurs during sensitive PWM onsets. Control over sampling rate, dynamic range, and resolution provides the user with tradeoffs that can optimize the system performance for the intended application. The SoC has been implemented in a 0.5-lm standard CMOS process, measuring 3.3 9 3 mm 2 and consuming 5.6 mW at ±1.5 V when all channels are active. Measured input referred noise for the entire system, including the receiver at 1 m distance, is 4.9 lV rms in 1 Hz-8.8 kHz range. Functionality of the WINeR-5 system has also been demonstrated in acute in vivo experiments.

A 100-channel hermetically sealed implantable device for wireless neurosensing applications

“…Such a wireless system must fulfill multiple stringent requirements for advancing neuroscience and the needs of clinical patients. Challenges include optimal ultralow-power circuit design, tight system integration, leak-proof device packaging, and compatibility with surgical implantation procedures [2][3][4][5][6][7][8].…”

An inductively powered scalable 32-channel wireless neural recording system-on-a-chip for neuroscience applications

“…We introduced a Wireless Integrated Neural Recording system (WINeR-5) in [6] as a substitute for hardwires in recording setups from freely moving animals in behavioral neuroscience research applications. This removes a source of motion artifacts and bias in the experimental results due to psychological effects of tethering.…”

“…Neural signals are amplified and filtered by an array of capacitively coupled fully differential LNAs with adjustable gain (67.8/78dB) and bandwidth (HPF: 0.1Hz-1kHz/LPF: 8kHz) [6]. Our prior experience with WINeR-5 showed that although each LNA consumes a small current (∼25μA), since there are 32 of them, the LNA block quickly becomes the dominant power consumer (42%).…”

Inductive Coupling

“…Several research groups have implemented active back-telemetry links for neural recording systems using commercial components (Obeid et al, 2003;Hawley et al, 2002, Gosalia et al, 2004 or custom ASICs (Lee et al, 2010;Yin and Ghovanloo, 2011;Chae et al, 2009;Miranda et al, 2010;Rizk et al, 2009;Mohseni and Najafi, 2004). In most of these designs the IMD Tx is significantly simplified to reduce the size and power consumption at the expense of more complexity in the external Rx.…”

“…A key limitation of the current wireless neural recording systems that are developed for neuroscience applications is the need for the animal subject to carry a large payload of batteries for continuous recording over several hours or even days (Lee et al, 2010;Yin and Ghovanloo, 2011;Chae et al, 2009). This may not be a major issue for larger animal subjects such as non-human primates (Gao et al, 2012;Rizk et al, 2009).…”