ADE7816 datasheet(19/48 Pages) AD

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Data Sheet

ADE7816

Rev. 0 | Page 19 of 48

Antialiasing Filters

Each analog input pin requires that a simple RC filter be connected

to the input. The role of the RC filter is to prevent aliasing. The

aliasing effect is caused by frequency components (which are

higher than half the sampling rate of the ADC) folding back and

appearing in the sampled signal at a frequency that is below half

the sampling rate. Aliasing is an artifact of all sampled systems.

For conventional current sensors, it is recommended that one

RC filter with a corner frequency of 5 kHz be used for the

attenuation to be sufficiently high at the sampling frequency

of 1.024 MHz. The 20 dB per decade attenuation of this filter

is usually sufficient to eliminate the effects of aliasing for

conventional current sensors (see Figure 26).

LOAD

PHASE

ADE7816

1kΩ

22nF

IAP

IAN

CURRENT

TRANSFORMER

Figure 26. Current Transformer Input Connections

However, a di/dt sensor, such as a Rogowski coil, has a 20 dB per

decade gain. This neutralizes the 20 dB per decade attenuation

produced by the low-pass filter (LPF). Therefore, when using a

di/dt sensor, a second pole is required. One simple approach is

to cascade one additional RC filter, thereby producing a −40 dB

per decade attenuation (see Figure 27).

LOAD

PHASE

ADE7816

1kΩ

22nF

100Ω

22nF

IAP

IAN

ROGOWSKI

COIL

Figure 27. Rogowski Coil Input Connections

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