Figure 13 shows a basic 2nd order p

Figure 13 shows a basic 2nd order post filter, for a net 3rd order filtering of the LTC1966 RMS calculation. It uses the 85kW output impedance of the LTC1966 as the first resistor of a 3rd order Sallen-Key active-RC filter. This topology features a buffered output, which can be desirable depending on the application. However, there are disadvantages to this topology, the first of which is that the op amp input voltage and current errors directly degrade the effective LTC1966 VOOS. The table inset in Figure 13 shows these errors for four of Linear Technology’s op amps.