A subthreshold ultra low power 22fJ/conversion flash ADC for RFID sensing applications

In this paper an ultra low power Flash ADC for RFID application is presented. Several techniques are used to further reduce the power consumption and relatively elevate the speed of the ADC. These techniques include a low power Track-and-Latch comparator with no static current, large resisters in the resister string, an optimum encoder with only 2 stages using subthreshold design with the aid of low supply voltage of 0.7v for resister string and 0.5v for all logic blocks. In this ADC by absolute approximation the occupied area is equal with area of 16 resisters in the string. The circuit designed in 0.18μm CMOS technology and simulations show that the 4-bit ADC consumes almost 14.5μW at 40MS/s and 93.8nW at 0.1MS/s; however, it minimally dissipates only 22fJ per each conversion step. The results show that the proposed ADC could seriously compete with other low power ADCs in RFID sensing applications such as SAR ADCs.