Temperature insenitive ultra low power 0.7 V supply input and reference driver for 8 bit ADC in 65 nm CMOS technology

Abstract

With CMOS technology scaling down, performance of ADCs has been improving in terms of area, low supply voltage and especially ultra-low power consumption. How ever, analog performance has not been advancing compared to progress of the digital performance as CMOS technology is scaling down. This causes the design of ultra-low power ADC input driver still challenging due to its analog architecture. Settling time requirements, ADC input capacitance, low noise and THD requirements limits perfor mance of ADC input driver for ultra-low power operation. On the other hand, off-chip drivers lead to usage of larger area unnecessarily. This thesis offers the design of an on-chip temperature insensitive, ultra-low power input and reference driver for 8 bit ADC with 0.7 V supply. Temperature insensitivity is an essential feature for temper ature measurement to avoid the degradation of ADC performance as the temperature varies. The proposed design is able to drive 8 bit ADC along operating temperature range (from -40◦C to 125◦C). The proposed ADC input driver performs single ended to differential signal conversion, buffering, amplitude scaling, output common-mode adjustment and filtering. In the thesis, an ultra-low power 0.7 V supply temperature sensor operating from -40◦C and 125◦C and 100 kSPS differential input SAR ADC with 1V full scale input range is used. ADC reference driver is configured as current controlled non-inverting unity gain buffer between bandgap reference circuit and ADC reference voltage pin. According to the post-layout simulation results, average power consumption over operating temperature range is 111.53 µW. As a worst case scenario, total output noise voltage is 1.418 mV at -40 ◦C. The input driver has a THD of -72.51 dB at 244 Hz and -70.88 dB at 976 Hz.