A novel charge-metering method for voltage mode neural stimulation

Abstract

Abstract-This paper presents a novel, fully-integrated circuit for achieving change-balanced voltage-mode neural stimulation based on a charge-metering technique. The proposed system uses two small on-chip capacitors, a counter, two comparators and a control-logic circuit to measure the charge delivered to the tissue. This has been designed to deliver a maximum charge stimulus of 10.24 nC within 100 µs. Simulated results show a charge delivery error of 0.4-4% and a maximum residual charge of −73 pC. Implemented in 0.18 µm CMOS, the total power consumption is 42 µW.

Neuromodulation: present and emerging methods

“…Looking to the future, we see a trend for multimodal neuromodulation—combining the advantages and mitigating the disadvantages of different modalities. Examples include combining current stimulation with voltage control to reduce power (Williams and Constandinou, 2013 ), voltage stimulation with current control (Luan and Constandinou, 2012 ), hybrid electro-optical stimulation (Duke et al, 2012 ; Mou et al, 2012 ), or integrating current controlled stimulation with microfluidics to reduce stimulation thresholds (Song et al, 2011 ). Electrical neural stimulation remains the gold standard in clinical use (especially for chronic use or in the PNS), however, for applications demanding increased efficacy, increased modulation complexity and reduced side-effects the days of using just electrical stimulation on its own may be numbered.…”

“… (A) Current-Controlled Stimulation (B) Voltage-Controlled Stimulation (C) Charge-Controlled Stimulation (D) Electrode-Electrolyte Interface model [Rs is solution spreading resistance, C dl is double layer capacitance, R t is charge transfer resistance (Luan and Constandinou, 2012 )] …”

“…Charge controlled stimulation combines voltage stimulation with a capacitor to limit or control the charge delivered to the electrodes (Ghovanloo, 2006 ; Bawa, 2008 ; Rosellini et al, 2011 ; Luan and Constandinou, 2012 ). In terms of biocompatibility and power consumption, this approach offers a mid-ground between current and voltage controlled stimulation, however, it is not yet been reported to be in clinical use.…”

Circuit Design Considerations for Power-Efficient and Safe Implantable Electrical Neurostimulators

“…1, the efficacy of stimulation is ensured by matching the amount of charge between subsequent stimulation pulses. In order to do so, a charge-metering circuit similar to the one presented in [19] is proposed. In this case, the circuit is not used to match the charge between the two phases of the biphasic stimulation pulse, but, instead, it is used to match the charge between the activation phases of subsequent biphasic pulses.…”