A Neurochemical Pattern Generator SoC With Switched-Electrode Management for Single-Chip Electrical Stimulation and 9.3 µW, 78 pA rms , 400 V/s FSCV Sensing

Abstract

This paper describes a system-on-chip (SoC) fabricated in AMS 0.35 µm 2P/4M CMOS for high-fidelity neurochemical pattern generation in vivo. The SoC uniquely integrates electrical stimulation with embedded timing management for generation of neurochemical patterns and 400 V/s fast-scan cyclic voltammetry (FSCV) sensing for subsequent assessment of fidelity in the generated profiles, and manages a novel switched-electrode scheme that eliminates the possibility of large stimulus artifacts adversely affecting electrochemistry. The SoC also leverages the discontinuous sampling inherent in FSCV to reduce the sensing power consumption by 87.5% to 9.3 µW from 2.5 V using a duty-cycled, 3rd-order, continuous-time, ΔΣ modulator (CT-ΔΣM) with an inputreferred noise current of 78 pA rms (dc -5 kHz) within an input current range of ±950 nA. Utilizing a transfer function that relates electrical stimulation of dopamine axons traversing the medial forebrain bundle (MFB) to evoked extracellular dopamine dynamics in the dorsal striatum of the forebrain, the correlation coefficient between predicted and measured dopamine temporal profiles was found to be 0.95 in an anesthetized rat.

Neurochemostat: A Neural Interface SoC With Integrated Chemometrics for Closed-Loop Regulation of Brain Dopamine

“…One recent example has facilitated such an extension for the first time by combining electrical microstimulation and neurochemical monitoring in a single-chip IC for high-fidelity dopamine temporal pattern generation in vivo [21], [22]. However, this IC still does not have any embedded computational capabilities for chemically resolving dopamine levels, measured by fast-scan cyclic voltammetry (FSCV) with a carbon-fiber microelectrode (CFM), and directly linking them to activation of the electrical stimulator.…”

A Wireless FSCV Monitoring IC With Analog Background Subtraction and UWB Telemetry

“…In a Nyquist ADC, the serialized unencoded data rate R b is given by $$R_b=N\times f_s,$$ where N is number of bits per sample, and f s is the Nyquist sampling rate. In an oversampling ΔΣ ADC, the undecimated unencoded data rate $R_b^{\prime }$ is given by $$R_b^{\prime }=\mathit{OSR}\times f_s.$$ In [9]–[11], the unencoded data rate of the transmitter is equal to the undecimated data rate of the ΔΣ modulator because the decimation filter is implemented on the receiver side due to its complexity, area and power. Comparing (11) and (12) with N = 9 and OSR = 32 reveals the ADC in this work yields a 3.5× reduction in the wireless data transmission rate compared to the ADC in [10].…”

“…This is because average power P avg in a duty-cycled IR-UWB TX is linearly proportional to the data rate R b , as given approximately by $$P_{\mathrm{italicavg}}=E_b\cdot R_b+P_0,$$ where E b is the energy efficiency (or energy per pulse), and P 0 is a constant representing leakage and overhead power. Equation (13) suggests that for energy efficiencies in the order of 100 pJ/pulse, duty-cycled IR-UWB transmitters operating at a data rate of 100 kbps consume a few tens of microwatts, compared to the milliwatt power consumption of the narrowband systems in [9]–[11]. This orders-of-magnitude reduction in TX power associated with duty-cycled IR-UWB telemetry is critical to enable long-term brain-behavior studies.…”

“…One drawback of the technique is the fact that the small (±10 nA) redox current indicating dopamine concentration is buried by the large (±500 nA) background current produced due to the charging of the double-layer capacitance of the electrode-electrolyte interface [4]. Recent wireless FSCV microsystems have overcome this limitation by using high-order delta-sigma (ΔΣ) modulation to acquire the full span of the background with reduced in-band quantization noise at the expense of increased wireless data transmission rates [9]–[11]. Since the background has been proven to be stable over several hundred scans [12], these systems waste a significant fraction of their limited power budget repeatedly resolving and transmitting the same background information over consecutive scans.…”

Multisensor Portable Meter for Environmental Applications

“…Concerning the measurement equipment, a miniaturized potentiostat fabricated in a silicon chip using CMOS technology was described [13]. Although the dimensions of this chip can be a few millimeters, it has been customized for a specific use, rather than intended for general uses.…”