A 0.042 mm^2 programmable biphasic stimulator for cochlear implants suitable for a large number of channels

This paper presents a compact programmable biphasic stimulator for cochlear implants. By employing double-loop negative feedback, the output impedance of the current generator is increased, while maximizing the voltage compliance of the output transistor. To make the stimulator circuit compact, the stimulation current is set by scaling a reference current using a two stage binary-weighted transistor DAC (comprising a 3 bit high-voltage transistor DAC and a 4 bit low-voltage transistor DAC). With this structure the power consumption and the area of the circuit can be minimized. The proposed circuit has been implemented in AMS 0.18μm highvoltage CMOS IC technology, using an active chip area of about 0.042mm. Measurement results show that proper charge balance of the anodic and cathodic stimulation phases is achieved and a dc blocking capacitor can be omitted. The resulting reduction in the required area makes the proposed system suitable for a large number of channels.