A CMOS detector system for fluorescent bio-sensing application

This system integrates a CMOS process compatible photodiode, a low noise capacitive trans-impedance amplifier (CTIA) and a 12-bit pipelined analog-to-digital converter (ADC). The chip fabricated in a 0.18-mum standard CMOS technology occupies 3 MMZ and consumes 37 mW. Experimental results show that the Nwell/Psub photodiode used in the fluorescent detecting experiment has a sensitivity of 0.1 A/W at 515 nm and a dark current of 3 nA/cm
²
. The maximum differential and integral nonlinearity of the designed ADC are +0.8 LSB and -3 LSB, respectively. With a solution volume of 0.5 mul, the detector system is able to detect the fluorescein solution concentration as low as 625 ng/ml. The minimum detectable fluorescent intensity and photocurrent are 18 nW/cm
²
and 36 fA, respectively.