A CMOS image sensor using high-speed lock-in pixels for stimulated Raman scattering (SRS) spectroscopy is presented in this paper. The effective SRS signal from the stimulated emission of SRS mechanism is very small in contrast to the offset of a probing laser source, which is in the ratio of 10-4 to 10-5. In order to extract this signal, the common offset component is removed, and the small difference component is sampled using switched-capacitor integrator with a fully differential amplifier. The sampling is performed over many integration cycles to achieve appropriate amplification. The lock-in pixels utilizes high-speed lateral electric field charge modulator (LEFM) to demodulate the SRS signal which is modulated at high-frequency of 20MHz. A prototype chip is implemented using 0.11μm CMOS image sensor technology.
A high speed Lateral Electric Field Modulator (LEFM) and lock-in pixels amplifiers for stimulated Raman
scattering (SRS)imager is presented. Since the generated signal from the SRS process is very small compared to
the offset signal, a technique suitable for extracting and amplifying the SRS signal is needed. The offset can be
canceled by tuning the phase delay between the demodulated pixel output signal and the sampling clock. The
small SRS signal in large offset is amplified by the differential integration. The proposed technique has been
investigated with an implementation of 64x8 pixels array using a pinned photodiode LEFM an lock-in pixels
amplifiers. Very small signal can be extracted from large offset signal. A ratio of the detected small SRS to
offset signal of less 10-5 is achieved.