A 0.18 μm CMOS fluorescent detector system for bio-sensing application

Abstract

A CMOS fluorescent detector system for biological experiment is presented. This system integrates a CMOS compatible photodiode, a capacitive trans-impedance amplifier (CTIA), and a 12 bit pipelined analog-todigital converter (ADC), and is implemented in a 0.18 µm standard CMOS process. Some special techniques, such as a "contact imaging" detecting method, pseudo-differential architecture, dummy photodiodes, and a T-type reset switch, are adopted to achieve low-level sensing application. Experiment results show that the Nwell/Psub photodiode with CTIA pixel achieves a sensitivity of 0.1 A/W at 515 nm and a dark current of 300 fA with 300 mV reverse biased voltage. The maximum differential and integral nonlinearity of the designed ADC are 0.8 LSB and 3 LSB, respectively. With an integrating time of 50 ms, this system is sensitive to the fluorescence emitted by the fluorescein solution with concentration as low as 20 ng/mL and can generate 7 fA photocurrent. This chip occupies 3 mm 2 and consumes 37 mW.

Differential integrator pixel architecture for dark current compensation in CMOS image sensors

“…The output voltage of each op-amp is equal to the simple integrator circuit described before: Figure 2.16. CTIA interface [36] In order to decrease the number of transistors in each pixel so that the fill factor is increased, the structure of the two amplifiers in Figure 2.18. can be modified into the more compact amplifier presented in Figure 2.19.…”