A Neuromodulator Frontend With Reconfigurable Class-B Current and Voltage Controlled Stimulator

Abstract

This letter presents a neuromodulator frontend that features a reconfigurable current and voltage mode stimulator for a bidirectional, neural interface. By implementing a capacitive high voltage (HV) to low voltage (LV) converter, a single-bit quantizer in the LV domain can be used to compare the difference between the electrode potential and the output of a 7-bit digital-to-analog converter. The digitized signal is integrated to generate a digital feedback signal, which controls a constant current stimulator in order to generate the desired output voltage by adjusting the output current. Thereby the stimulator can deliver up to ±10 mA of output current and ±6 V of stimulation voltage. The stimulation unit is connected over HV protection switches to a neural recorder that features a tunable high-pass cut-off frequency and impulse-based bioimpedance estimation, to form a bidirectional channel. The total consumed silicon area of the frontend is 0.45 mm2 for recording and stimulation. In standby mode the stimulator can be completely disconnected from its biasing, which leads to a power consumption of less than 1 ${\mu }\text{W}$ . The class-B operation during voltage stimulation yields an active power consumption, which is dominated by the stimulator output current in both voltage and current mode.