The convergence of self-powered technology with on-body wearable applications creates impactful opportunities for more personalized healthcare. PPG sensing is recognized as a primary method for recovering physiological information but remains relatively high-power compared to the available energy harvesting options in an on-body self-powered context, limiting reliability. This paper introduces a PPG sensing model based on a differential regulated cascode TIA to demonstrate the power, signaling, and circuit tradeoffs that exist for self-powered PPG operation. The model shows that body-worn uW to sub-uW self-powered PPG operation is achievable and provides insight on challenges and limitations.