Low-noise CMOS Fluorescence Sensor

Abstract

Abstract-This paper reports a novel integrated circuit for fluorescence sensing. The circuit implements a differential readout architecture in order to reduce the overall noise figure. The circuit has been fabricated in a commercially available 0.5 µm CMOS technology. Preliminary results show that the reset noise is reduced by a factor of 1.42 and the readout noise by a factor of 9.20 when the pixel is operated in differential mode versus singleended mode. Spectral responsivity characteristics show that the photodiodes are most sensitive at 480 nm. Using a commercially available emission filter, the sensor was able to reliably detect a concentration of Fura-2 as low as 39 nM. The sensor was used to perform ratiometric measurements and was able to reliably detect a free calcium concentration of 17 nM.

Noise model, analysis and characterization of a differential active pixel sensor

“…The results show that both reset and readout noise increase of 117% and 58% due to increased complexity within the circuit. However, in realistic applications and measurement scenarios [11] including portable system on a chip devices the differential readout provides the practical advantage of suppression of correlated noise within the readout path, which improves the overall system noise performance. We would like to thank Dr. Honghao Ji, and Marc Dandin for sensor development and technical discussion.…”

“…Section IV describes the experimental setup and results. This work is summarized in Section V. Figure 1 shows the schematic of the sensor which was previously reported [11]. Here we present a thorough noise analysis and experimental characterization.…”

Confession session: Learning from others mistakes

“…The monochromator output signal is coupled to an integrating sphere whose interior is coated with a diffuse reflector, so that the optical signals at the sphere's output ports are spatially uniform and equal in magnitude. The whole system is computer controlled and can accommodate various CMOS sensor boards (Dandin et al 2007, Sanders et al 2008.…”

“…The junction is highly responsive at = 550 nm, and we concluded that this caused the unusually high response. The issue was rectified by purchasing a set of order sorting filters from the vendor (Sander et al, 2007).…”

Single Photon Avalanche Detectors in Standard CMOS

“…The detection limit of the detector to Fura-2 was determined as the lowest concentration at which the count rate exceeded the background by at least one standard deviation, which occurred at 15.625 nM. In comparison with a low noise photodetector which had a detection limit of 39 nM, the SPAD detector is a factor of 2.3 better [9]. We are currently working on improving this detection limit by reducing the coupling efficiency of the excitation light with the chip.…”