Research And Implementation Of Charge Balance Technology Suitable For Neural Stimulation Integrated Circuits

With the development of multi-disciplinary cross-cooperation,the neural stimulator,as the crystallization of scientific research between the medical field and integrated circuit field,has been a research hotspot for nearly half a century.Nerve stimulators can not only treat some physical nerve damage,but also treat psychological diseases by stimulating nerves.As a type of medical product,the neural stimulator not only is it necessary to complete the treatment of a specific disease,but it must also ensure safety without causing new harm to the patient.However,the current neural stimulator has a fatal shortcoming.That is,after the stimulation operation is performed,the electrode has a part of the charge brought by the neural stimulator,which causes the electrode to fail to return to the original state.Human beings have not yet reached the point of exhaustion in their own exploration of the body,and each individual’s situation is different.Therefore,whether these residual charges will cause harm to the body is still only in the experimental stage,and it is not representative of all individuals.In order to ensure the safety of patients and improve the applicability of the neural stimulator,many charge balancing techniques have been proposed to reduce the amount of residual charge on the electrodes.The charge balance technology proposed in this paper is: to construct an indirect synchronous detection system outside the main(Digital-to-Analog Converter)DAC and the electrode.The synchronous detection system completes the real-time monitoring of the amount of charge on the electrodes without disturbing the stimulation’s operation.The synchronous detection system is composed of a current reduction circuit,a current integrator circuit and a voltage comparator circuit.By analyzing the effect of circuit error on the unbalanced charge,a corresponding compensation circuit is proposed to compensate the unbalanced charge,and then the amount of unbalanced charge in a single stimulation cycle is less than 15 p C.In addition,in view of the electrode voltage shift caused by the imbalanced charges accumulated after the multiple stimulation cycles,this paper uses short pulse insertion compensation technology to ensure that the electrode voltage shift is less than ± 25 m V.Based on this charge balance technology,this paper uses the TSMC 180 nm process to design the circuit and layout of the neural stimulator circuit.Through the postsimulation results,the feasibility of the charge balance technology has been verified.