This is a four layer board. All the critical signals are routed in the top layer as shown in Figure 5-3. The power stage and 0.1 Hz to 10 Hz band pass filter are EMI shielded separately. The grounds for the band pass filter and the power stage are connected only at one place to verify that any power supply noise (ground return path) does not couple with critical signal in filter stage. Critical signals are ground shielded. Input and output are SMA connectors to avoid impact of EMI. All the signals for parallel op-amps in the first stage are routed with symmetry to avoid any mismatch between them. Second layer (Figure 5-4) is complete GND layer for decoupling. Power signal is routed in the third layer (Figure 5-5) for all the op-amps. Two of the four big electrolyte capacitors in first stage 0.1 Hz high pass filter are placed in the bottom layer (Figure 5-6 ) to save space. The bottom layer has low frequency bypass capacitors at all the corners of the shielded region.