An Implantable Neural Stimulator IC With Anodic Current Pulse Modulation Based Active Charge Balancing

Abstract

Implantable electrical stimulators can be used to treat a variety of neurological disorders and restore paralyzed body functions. In electrical neural stimulation, the stimulator circuit with safe charge balancing is essential to minimize damage to electrodes and biological tissue. In this paper, an implantable current-mode neural stimulator for long-term safe electrical stimulation is presented. Anodic current pulse modulation active charge balancing technique is proposed to keep the residual voltage on the electrode within the safe window, which enables long-term safe stimulation. To ensure more complete charge balancing, the proposed active charge balancing technique can also be used with passive electrode shorting. Transistor stacking and dynamic gate biasing techniques can prevent the breakdown of standard MOSFET devices from high supply voltages, which enable the implementation of output current driver and charge balancing circuits without using HV process. The stimulator IC designed with 0.18-µm standard CMOS process can generate up to 1 mA of stimulation current and only consumes an area of 0.11 mm². Since all functions are implemented on-chip without using external components, the proposed stimulator IC is suitable for highdensity implantable stimulation applications.

A 2‐mA charge‐balanced neurostimulator in 0.18‐μm/1.8 V standard CMOS process

“…We also used electrode shorting technique to remove the extra charges after biphasic stimulation. 49,50,66 The switches based on NMOS transistors are used to pull down extra charges to the ground. A self-adaption bias circuit, which was proposed by Lee et al, 65 is used here.…”

A 24-Channel Neurostimulator IC With Channel-Specific Energy-Efficient Hybrid Preventive-Detective Dynamic-Precision Charge Balancing

“…The magnitude of the push/pull current source used for the detective loop's charge balancing (I balance ) is chosen based on the application, and also as a tradeoff between the latency and the accuracy of compensation. Increasing this current's magnitude allows for quick neutralization of the accumulated charges but comes at the cost of losing neutralization precision as well as risking an unintended stimulation of neurons [16], [17], [33]. As will be described in details (Section II.D), we have chosen the I balance 's value to ensure safe and timely neutralization with sufficient accuracy demanded by the application.…”

“…On the other hand, activating the balancing circuit at every inter-pulse resting interval significantly increases power consumption. Additionally, since the balancer should inject sub-µA-pulses (to avoid unintended stimulation [17], [33], [34]), for a large persistent imbalance, the required inter-pulse resting interval could become considerably longer, thus, limiting the maximum stimulation frequency. It should also be noted that using these high-frequency balancing pulses after every stimulation pulse could cause major side effects on neural pathways which affect the long-term effectiveness of neural stimulation [35].…”

A Multi-Channel Stimulator With High-Resolution Time-to-Current Conversion for Vagal-Cardiac Neuromodulation

“…Electrode discharging is often required to remove any residual charge by either actively sending extra short-burst current pulses or temporarily passively shorting the electrodes together [facilitated by switch S3 in Fig. 2(a) and (b)] after each biphasic pulse for better charge balancing [26].…”