PCB design review: analog routing
Can you think of anything I could do differently?


Yes, I can think of one thing. Start learning how to model PCB parasitic component values. This takes some of the mystery out of PCB design and allows one to design circuits without worrying what the PCB will do to the design.

A PCB trace actually looks like this: 

Source: https://www.ecnmag.com/article/2017/06/plague-parasites

Whenever you add a pcb trace between two points, your adding a small amount of inductance and capacitance. The PCB trace has capacitance between it and the conductor below it (any two pieces of conductors\metals can be modeled as a capacitor).


Source: https://www.ecnmag.com/article/2017/06/plague-parasites

Just glancing at the schematic, I see it more like this after layout on the PCB. Each trace adds milliohms of resistance an nH of inductance. Inductance slows electrical signals down so making the traces small is a good idea because it minimizes inductance and resistance.


The biggest problem I see is the ground of U1 and , with the small trace size, this is creating inductance and resistance on the ground of U1. If the signals of U1 are changing very fast (10's of MHz), you might have a problem with common mode noise on U1 because of the inductance of the two vias. While its great that you chose to route the ground of U1 to be the same of the photodiode, you might be able to rotate U1 and route the ground continuously on the top layer.