A 17-bit 104-dB-DR High-Precision Low-Power CMOS Fluorescence Biosensor With Extended Counting ADC and Noise Cancellation

This paper presents a high-dynamic range CMOS biosensor fusing a photosensing module with a high-precision extended counting analog-to-digital converter (ADC) with noise cancellation to detect florescence neural signal fluctuations of very low incident power. The 7 MSBs are resolved by a first order continuous-time resettable $\Sigma \triangle \mathrm {A}\mathrm {D}\mathrm {C}$, whereas the residue voltage is quantized by a 10-bit single slope ADC for enabling wide dynamic range and high precision fluorescence sensing. Low-frequency imperfections are canceled out by an embedded noise cancellation scheme which is subtracting the noise and the offset using switches and capacitors. The quantizer is shared between the $\Sigma \triangle $ and the single slope ADC to decrease the chip size and to improve energy-efficiency. The proposed optoelectronic biosensor is implemented in a $0.18-\mu \mathrm {m}$ CMOS technology, consuming $93 \mu \mathrm {W}$ from a 3.3-V supply voltage while achieving a DR of 104dB, and a minimum detectable current of $400-fA_{rms}$, for a conversion time of $506.5\mu s.$