A 1 V 10 bit 25 kS/s VCO-based ADC for implantable neural recording

A differential-input A/D converter (ADC) based on voltage-controlled oscillator (VCO) is proposed for implantable bioelectronics. Two single-ended VCO-based ADCs are matched and combined to support differential input, hence suppressing the common-mode interference and even harmonics distortion. A 10-bit binary subtraction circuit, which is utilized to process the digital output of two matched ADCs, generates the final digital output. The subtraction circuit is realized with Domino logic gates for further reduction in power consumption and chip area. Designed with 0.18 μm CMOS process, the 10 bit 25 kS/s VCO-based ADC can operate under 1 V power supply. The active area of this ADC is 270 μm × 100 μm, much smaller than a successive-approximation-register (SAR) ADC with similar performance.