Compact, Energy-Efficient High-Frequency Switched Capacitor Neural Stimulator With Active Charge Balancing

Safety and energy efficiency are two major concerns for implantable neural stimulators. This paper presents a novel high-frequency, switched capacitor (HFSC) stimulation and active charge balancing scheme, which achieves high energy efficiency and well-controlled stimulation charge in the presence of large electrode impedance variations. Furthermore, the HFSC can be implemented in a compact size without any external component to simultaneously enable multichannel stimulation by deploying multiple stimulators. The theoretical analysis shows significant benefits over the constant-current and voltage-mode stimulation methods. The proposed solution was fabricated using a 0.18 μm high-voltage technology, and occupies only 0.035 mm2 for a single stimulator. The measurement result shows 50% peak energy efficiency and confirms the effectiveness of active charge balancing to prevent the electrode dissolution

Neurostimulator with Waveforms Inspired by Nature for Wearable Electro-Acupuncture

The work presented here has 3 goals: establish the need for novel neurostimulation waveform solutions through a literature review, develop a neurostimulation pulse generator, and verify the operation of the device for neurostimulation applications. The literature review discusses the importance of stimulation waveforms on the outcomes of neurostimulation, and proposes new directions for neurostimulation research that would help in improving the reproducibility and comparability between studies. The pulse generator circuit is then described that generates signals inspired by the shape of excitatory or inhibitory post-synaptic potentials (EPSP, IPSP). The circuit analytical equations are presented, and the effects of the circuit design components are discussed. The circuit is also analyzed with a capacitive load using a simplified Randles model to represent the electrode-electrolyte interface, and the output is measured in phosphate-buffered saline (PBS) solution as the load with acupuncture needles as electrodes. The circuit is designed to be used in different types of neurostimulators depending on the needs of the application, and to study the effects of varying neurostimulation waveforms. The circuit is used to develop a remote-controlled wearable veterinary electro-acupuncture machine. The device has a small form-factor and 3D printed enclosure, and has a weight of 75 g with leads attached. The device is powered by a 500 mAh lithium polymer battery, and was tested to last 6 hours. The device is tested in an electro-acupuncture animal study on cats performed at the Louisiana State University School of Veterinary Medicine, where it showed expected electro-acupuncture effects. Then, a 2-channel implementation of the device is presented, and tested to show independent output amplitude, frequency, and stimulation duration per channel. Finally, the software and hardware requirements for control of the wearable veterinary electro-acupuncture machine are detailed. The number of output channels is limited to the number of hardware PWM timers available for use. The Arduino software implements PWM control for the output amplitude and frequency. The stimulation duration control is provided using software timers. The communications protocol between the microcontroller board and Android App are described, and communications are performed via Bluetooth

Comments on "Compact, Energy-Efficient High-Frequency Switched Capacitor Neural Stimulator With Active Charge Balancing" (vol 11, pg 878, 2017): Comments on 'Compact, energy-efficient high-frequency switched capacitor neural stimulator with active charge balancing (IEEE Transactions on Biomedical Circuits and Systems (2017) 11:4 (878–888) DOI: 10.1109/TBCAS.2017.2694144)

This manuscript points out some mistakes in the Introduction and in the table of comparison of a paper already published in this journal by Hsu and Schmid [1]. Although the main claim of [1] is still preserved, we believe the paper needs to be rectified for scientific correctness of the work. In [1], the first High Frequency Switched-Capacitor (HFSC) stimulator is presented. The stimulation voltage is derived from the main supply by using an 1 : 1 switched-capacitor DC-DC converter. This particular topology of DC-DC converter operates as a resistor [2]. The further away the output voltage is from the input voltage, the lower the power efficiency is. As a result, the output voltage of the DC-DC converter, and therefore the total charge delivered to the tissue, can only be regulated at the expense of the power efficiency. Section I of [1], provides an overview of the most recently published works in the field of electrical stimulation. Based on the stimulation mode, Hsu and Schmid classify the papers into three categories, named voltage-mode stimulation (VMS), current-mode stimulation (CMS) and switched-capacitor stimulation (SCS). In [1], thework presented in [3] has been classified as SCS.However, [3] proposes CMS which adapts the voltage supply of the neurostimulator to the voltage across the electrodes. In [1], the work presented in [4] has been classified as VMS. However, [4] proposes a CMS. In fact, an inductor-based DC-DC converter without the output capacitance is used to deliver the charge to the tissue. Section V of [1] provides a table of comparison, in which the performances of the stimulator circuit are compared with some relevant contributions found in literature. Several errors have been found in the comparison table. The entries in bold characters and red colour of Table I below corrects the table of comparison presented in [1]. II. CONCLUSION The aim of this comment is two-fold. Firstly, it corrects a classification of the most recent works, which was presented in the Introduction of a paper previously published in this journal [1]. Secondly, it corrects some mistakes in its table of comparison. Although errors have been found, the main claim of [1], and hence its scientific contribution, are still preserved. [Table Presented].Bio-Electronic

Comments on "Compact, Energy-Efficient High-Frequency Switched Capacitor Neural Stimulator With Active Charge Balancing" (vol 11, pg 878, 2017): Comments on 'Compact, energy-efficient high-frequency switched capacitor neural stimulator with active charge balancing (IEEE Transactions on Biomedical Circuits and Systems (2017) 11:4 (878–888) DOI: 10.1109/TBCAS.2017.2694144)

This manuscript points out some mistakes in the Introduction and in the table of comparison of a paper already published in this journal by Hsu and Schmid [1]. Although the main claim of [1] is still preserved, we believe the paper needs to be rectified for scientific correctness of the work. In [1], the first High Frequency Switched-Capacitor (HFSC) stimulator is presented. The stimulation voltage is derived from the main supply by using an 1 : 1 switched-capacitor DC-DC converter. This particular topology of DC-DC converter operates as a resistor [2]. The further away the output voltage is from the input voltage, the lower the power efficiency is. As a result, the output voltage of the DC-DC converter, and therefore the total charge delivered to the tissue, can only be regulated at the expense of the power efficiency. Section I of [1], provides an overview of the most recently published works in the field of electrical stimulation. Based on the stimulation mode, Hsu and Schmid classify the papers into three categories, named voltage-mode stimulation (VMS), current-mode stimulation (CMS) and switched-capacitor stimulation (SCS). In [1], thework presented in [3] has been classified as SCS.However, [3] proposes CMS which adapts the voltage supply of the neurostimulator to the voltage across the electrodes. In [1], the work presented in [4] has been classified as VMS. However, [4] proposes a CMS. In fact, an inductor-based DC-DC converter without the output capacitance is used to deliver the charge to the tissue. Section V of [1] provides a table of comparison, in which the performances of the stimulator circuit are compared with some relevant contributions found in literature. Several errors have been found in the comparison table. The entries in bold characters and red colour of Table I below corrects the table of comparison presented in [1]. II. CONCLUSION The aim of this comment is two-fold. Firstly, it corrects a classification of the most recent works, which was presented in the Introduction of a paper previously published in this journal [1]. Secondly, it corrects some mistakes in its table of comparison. Although errors have been found, the main claim of [1], and hence its scientific contribution, are still preserved. [Table Presented].</p