An Area- and Energy-Efficient 16-Channel, AC-Coupled Neural Recording Analog Frontend for High-Density Multichannel Neural Recordings

Abstract

We present an AC-coupled modular 16-channel analog frontend with 1.774 fJ/c-s∙mm2 energy- and area-product for a multichannel recording of broadband neural signals including local field potentials (LFPs) and extracellular action potentials (EAPs). To achieve such a small area- and energy-product, we employed an operational transconductance amplifier (OTA) with local positive feedback, instead of a widely-used folded cascode OTA (FC-OTA) or current mirror OTA for conventional neural recordings, while optimizing the design parameters affecting performance, power, and area trade-offs. In addition, a second pole was strategically introduced in the LNA to reduce the noise bandwidth without an in-channel low-pass filter. Compared to conventional works, the presented method shows better performance in terms of noise, power, and area usages. The performance of the fabricated 16-channel analog frontend is fully characterized in a benchtop and an in vitro setup. The 16-channel frontend embraces LFPs and EAPs with 4.27 μVrms input referred noise (0.5–10 kHz) and 53.17 dB dynamic range, consuming 3.44 μW and 0.012 mm2 per channel. The channel figure of merit (FoM) of the prototype is 147.87 fJ/c-s and the energy-area FoM (E-A FoM) is 1.774 fJ/c-s∙mm2.

A Microdevice in a Submicron CMOS for Closed-Loop Deep-Brain Stimulation (CLDBS)

“…The LNA and neurostimulator were designed and fabricated in the CMOS (65 nm) from TSMC. Table 4 compares the LNA with a few related key works found in the literature [9,10,[21][22][23][26][27][28][29][30][31]. The figure-of-merit (FOM) was calculated to better rank and compare this work with the others with respect to the internal noise-power consumption tradeoff.…”

“…The inverter introduced half the amount of power noise. Consequently, the NEF is reduced by √ 2; implementations with processes with higher minimum lengths [11,[26][27][28][29][30][31] display better NEFs.…”

“…The figure emphasizes the two circuits presented in this paper. <math display='block'> <mrow> <msqrt> <mn>2</mn> </msqrt> </mrow> </math> <!--MathType@End@5@5@ --> ; implementations with processes with higher minimum lengths [11,[26][27][28][29][30][31] display better NEFs.…”

Single-Stage CMOS Operational Transconductance Amplifiers (OTAs): A Design Tutorial

“…Moreover, in order to further increase the A o , the folded cascode structure has been adopted as the first stage of a multi-stage OP-AMP [36]. Lastly, the current mirror OTA has been used as the error amplifier of DC-DC converters and LDOs [18][19][20] or as the feedforward amplifier of neural recording amplifiers [13,14]. In power converters, the error amplifier often needs to be fast since the output voltage or the load condition can be changed rapidly.…”

“…OTA-based integrators with an inherent high gain and low-pass frequency response have been used in delta-sigma analog-to-digital converters (ADCs) [10][11][12]. Moreover, OTAs themselves have served as feedforward amplifiers of closed-loop systems such as capacitively coupled instrumentation amplifiers (CCIAs) [13][14][15] and power ICs [16][17][18][19][20] thanks to their high gain performance. The versatility and wide applicability of OTAs make them indispensable in various analog and mixed-signal circuit designs, emphasizing the paramount importance of OTA design.…”