Figure 4-3 shows a switched capacitor CSA. In this topology, flying capacitors are used to sample the voltage across the shunt resistor and stripping off the high-voltage common-mode component from the input. The input bias current can be very small when it is made up of only the capacitor charging and discharging current. A second stage is used to provide additional gain and accomplish differential to single-ended voltage conversion. The second stage is normally a simple diff amp.