An asynchronous 8-bit 5 MS/s pipelined ADC for biomedical sensor based applications

Integrated biomedical sensors are used in biomedical devices which monitor vital bio-signals such as ECG, EMG, AAP, etc., whose maximum frequency range up to few MHz. Such integrated systems require analog to digital converters with Megahertz conversion rate. This paper presents a novel architecture of asynchronous pipelined analog to digital converter with emphasis on elimination of external clock for integrated biomedical sensor based applications. The main innovative feature of the proposed pipelined ADC is that it operates without any external timing signal and behaves like a combinational logic for a given analog input. Complete digital conversion is obtained by asynchronously propagating the partial conversions and the residues through the various stages. The only requirement for the ADC is an external trigger signal from the sensors. The proposed 8 bit ADC implemented in UMC 0.18 μm CMOS technology has a sampling rate of 5 MHz, with power dissipation of 30 mW and has an active area of 0.8544 mm².