Fig. 1. The circuit model of LAPS

Fig. 2. The block diagram of LAPS orthogonal phase detection system

Fig. 3. The block diagram of the orthogonal phase detection

Fig. 4. Flowchart of LAPS detection

Fig. 5. Detection results of pH by LAPS

Fig. 6. Curve local magnification diagram

Fig. 7. The effect of weakening light intensity on I-V and P-V characteristic curve