RFI Suppression Circuitry for AD620 Series Instrumentation Amplifiers

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The figure shows an RFI circuit for a general-purpose instrumentation amplifier, for example, the AD620 series, which has higher noise (12nV/Hz1/2) and lower bandwidth than the AD8221.

Accordingly, the same input resistor is employed, but the capacitance of capacitor C2 is increased approximately five times to 0.047 μF to provide sufficient RF attenuation. Using the component values ​​shown in the figure, the -3dB bandwidth of the circuit is approximately 400Hz; by reducing the resistance of resistors R1 and R2 to 2.2kΩ, the bandwidth can be increased to 760Hz. It should be noted that do not easily increase the bandwidth. It requires the instrumentation amplifier circuit described above to drive a lower impedance load, resulting in a somewhat reduced input overload protection.