A capacitive DAC with custom 3-D 1-fF MOM unit capacitors optimized for fastsettling routing in high speed SAR ADCs

【摘要】 Asynchronous successive approximation register(SAR) analog-to-digital converters(ADC) feature high energy efficiency but medium performance.From the point of view of speed,the key bottleneck is the unit capacitor size.In this paper,a small size three-dimensional(3-D) metal-oxide-metal(MOM) capacitor is proposed.The unit capacitor has a capacitance of 1-fF.It shapes as an umbrella,which is designed for fast settling consideration.A comparison among the proposed capacitor with other 3-D MOM capacitors is also given in the paper.To demonstrate the effectiveness of the MOM capacitor,a 6-b capacitive DAC is implemented in TSMC 1P9 M 65 nm LP CMOS technology.The DAC consumes a power dissipation of 0.16 mW at the rate of 100 MS/s,excluding a source-follower based output buffer.Static measurement result shows that INL is less than ± 1 LSB and DNL is less than ±0.5 LSB.In addition,a 100 MS/s 9-bit SAR ADC with the proposed 3-D capacitor is simulated.更多还原

【Abstract】 Asynchronous successive approximation register(SAR) analog-to-digital converters(ADC) feature high energy efficiency but medium performance.From the point of view of speed,the key bottleneck is the unit capacitor size.In this paper,a small size three-dimensional(3-D) metal-oxide-metal(MOM) capacitor is proposed.The unit capacitor has a capacitance of 1-fF.It shapes as an umbrella,which is designed for fast settling consideration.A comparison among the proposed capacitor with other 3-D MOM capacitors is also given in the paper.To demonstrate the effectiveness of the MOM capacitor,a 6-b capacitive DAC is implemented in TSMC 1P9 M 65 nm LP CMOS technology.The DAC consumes a power dissipation of 0.16 mW at the rate of 100 MS/s,excluding a source-follower based output buffer.Static measurement result shows that INL is less than ± 1 LSB and DNL is less than ±0.5 LSB.In addition,a 100 MS/s 9-bit SAR ADC with the proposed 3-D capacitor is simulated.更多还原