A 45 uW 13 pJ/conv-step 7.4-ENOB 40 kS/s SAR ADC for digital microfluidic biochip applications

In recent years Digital Micro-fluidic Bio-chips have become a suitable choice for point of care diagnostics. These devices can detect various properties of human blood by means of an optical detection technique. The data acquisition is generally done using a LED-photodiode setup working in conjunction with the biochip. The voltage signal obtained at the photodiode output needs to be converted into digital data for further processing. A low power 8 bit SAR ADC is designed for this purpose and implemented in UMC 180 nm technology. The functionality testing of the ADC is done using Spectre simulator of Cadence Analog Design Environment. The ADC consumes about 45 μWof power at 13 pJ/conv-step from a 1.8 V supply at 40 kS/s and achieves a SNDR of 46.5 dB, ENOB of 7.4 bits at a signal bandwidth of 10kHz. Mismatch analysis has been done by a set of Monte Carlo Simulations in Cadence. Even in worst case condition with 5% capacitance mismatch, the ADC achieves a SNDR of 43 dB, ENOB of 7 bits without any missing code.