Fully implantable, multi‐channel microstimulator with tracking supply ribbon, multi‐output charge pump and energy recovery

Abstract

A novel energy‐efficient approach dedicated to high‐density implantable stimulators such as visual prostheses is presented. Energy efficiency of the approach proposed in this work is achieved through two ideas: the ‘tracking supply ribbon’ technique and ‘reverse charge pumping’. The proposed approach is implemented, in the multi‐channel case, in such a way that power efficiency of each stimulation channel is enhanced according to its specific voltage/current condition and independently from other channels. For this purpose, a multi‐channel power‐efficient charge pump circuit with small integrated capacitors is proposed. Based on the proposed approach, a fully integrated 16‐channel stimulation backend for a visual prosthesis was designed and simulated in the transistor level in a standard 0.18‐μm triple‐well CMOS technology, occupying 1.41 mm2 of silicon area. According to post‐layout simulation results, power savings of up to 74% for a single channel and 81.5% for multiple channels are achieved compared to the conventional output stage with a constant supply voltage. Designed for the proposed stimulation backend, the charge pump generates output voltages of 3.48 V, −1.69 V, −3.38 V, and −5.05 V out of a 1.8 V input voltage and exhibits average power efficiency of 92.8% and 86.8% for one‐ and three‐stage circuits, respectively, all in the case of a 100 μA current load. All the aforementioned results are based on post‐layout simulation. Moreover, a proof‐of‐concept prototype was developed using off‐the‐shelf components in order to demonstrate the operation of the proposed tracking supply ribbon idea.

Energy Savings of Multi-Channel Neurostimulators with Non-Rectangular Current-Mode Stimuli Using Multiple Supply Rails

“…A more popular approach is to employ a DC/DC converter at the implant site to generate the adaptive supply rail(s) out of the constant DC voltage generated by either the wireless link interface or a battery [4], [7]- [9]. The proposed DC/DC converters are often based either on inductive buck/boost converters (Fig.…”

“…While an inductive approach benefits from continuous resolution for generating the voltage and current required at the output stage, it comes at the expense of off-chip inductor(s) and more limited MRI compatibility. Charge pump circuits ( [4], [9]) can benefit from fully-integrated architectures but with a limited resolution for the generated adaptive supplies.…”

“…1.d) at the cost of longer stimulation duration or higher amplitude for the highfrequency pulsed stimuli. Alternatively, a multi-output charge pump has been proposed in [4] (Fig. 1.f), where each channel connects to one of the charge pump outputs based on its instant voltage/current requirement, independent of other channels.…”

Energy efficiency of pulse shaping in electrical stimulation: the interdependence of biophysical effects and circuit design losses

“…A possible solution to reduce the overhead losses in CMS is dynamic voltage scaling (DVS) [8][9][10][11][12][13][14][15]. In DVS, the supply voltage is dynamically scaled to minimize the voltage drop across the current driver.…”

“…The first method scales the supply voltage by modulating the incoming AC power signal [8,9]. The second method uses (on-chip) adaptive DC/DC converters, for example, inductive buck/ boost converters [10,11] or switched-capacitor charge pumps [12][13][14][15]. The signal modulation and inductive DC/DC converter approaches benefit from a continuous output voltage range but suffer from limited scalability.…”