First off, the terminology I'm using could be complete rubbish - I'm still learning
I have a mixed signal board for measuring bio-signals. The 4 layer board will have a split ground plane, analog ground and main ground (for a microcontroller, SD card, extra sensors, etc), star connected at the power pins through a ferrite bead. Previous versions (which I did not design) have had significant problems with noise.
Should the analog circuitry (mostly op-amps, etc.) have additional decoupling capacitors near the physical chips, in addition to the caps at the outputs of the DC/DC and charge pump that are powering them? similar to the picture below.
Assuming that it should have the decoupling caps, what size and why? The DC-DC and charge pump are in the range of 100s of KHz to a few MHz, while the analog signals we are interested in are less than 100Hz, centred around 10Hz
Finally, all componants are Imperial 0805 packages (for convenience, still prototyping). The op-amps are 0PA2277 (additional question: is it better to use OPA4277, with 4 op-amps per package instead of 2, in terms of noise performance?).