For wearable biomedical devices, it is essential to detect target signals under high noise and strong interferences. Moreover, it is critical to realize the system with compact size and easy implementation. To address both goals, this paper presents a novel chip-based photoacoustic (PA) sensor called QuACL. By leveraging the adaptive coherent lock-in technique, the high sensitivity and specificity for detecting target signals can be achieved. In-phase and quadrature PA templates are specifically designed based on the profile of the target signal and are generated by the FPGA board and the DAC board. The received signal is correlated with the templates to capture, track, and recover the target PA signal. Fabricated in 65 nm CMOS technology, the chip-based sensor system occupies only 0.6 mm2 area. The robustness and versatility of the QuACL sensor system are verified by the experiments on discerning and recovering weak PA signals accurately.