For optical bio sensor on phone applications, we suggest modules instead of AFE for below reasons:
1, the size constraints. Nowadays, the space left for sensor is very small. We use all kinds of small parts to replace big parts to save space for display and battery. If use AFE, extra LED and PD is needed which will definitely requires more space.
2, optical sensor module PPG signal is good enough for phone applications as the PPG signal is mainly from somewhere of hands. This is unlike to wrist band or watch applications which needs more LEDs and PDs to get better PPG signal from wrist.
3, Maxim has shipped over 200Mu optical bio sensor modules for on phone applications. We have proven performance and manufactory quality control experience.