ADFS7124-8BBCPZ datasheet(57/93 Pages) AD

57 / 93 page

Data Sheet

ADFS7124-8

DIGITAL FILTER

analog.com

Rev. 0 | 57 of 93

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FREQUENCY (Hz)

Figure 85. Sinc4 Filter Response (50 SPS Output Data Rate, Zero Latency

Disabled or 12.5 SPS Output Data Rate, Zero Latency Enabled)

Figure 86 shows the frequency response of the sinc4 filter when

the output data rate is programmed to 60 SPS and zero latency is

disabled. For the same configuration but with zero latency enabled,

the filter response remains the same but the output data rate is 15

SPS. The sinc4 filter provides 60 Hz (±1 Hz) rejection of 120 dB

minimum, assuming a stable controller clock.

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Figure 86. Sinc4 Filter Response (60 SPS Output Data Rate, Zero Latency

Disabled or 15 SPS Output Data Rate, Zero Latency Enabled)

When the output data rate is 10 SPS with zero latency disabled or

2.5 SPS with zero latency enabled, simultaneous 50 Hz and 60 Hz

rejection is obtained. The sinc4 filter provides 50 Hz (±1 Hz) and

60 Hz (±1 Hz) rejection of 120 dB minimum, assuming a stable

controller clock.

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FREQUENCY (Hz)

Figure 87. Sinc4 Filter Response (10 SPS Output Data Rate, Zero Latency

Disabled or 2.5 SPS Output Data Rate, Zero Latency Enabled)

Simultaneous 50 Hz/60 Hz rejection can also be achieved using the

REJ60 bit in the filter register. When the sinc filter places a notch

at 50 Hz, the REJ60 bit places a first order notch at 60 Hz. The

output data rate is 50 SPS when zero latency is disabled and 12.5

SPS when zero latency is enabled. Figure 88 shows the frequency

response of the sinc4 filter. The filter provides 50 Hz ± 1 Hz and 60

Hz ± 1 Hz rejection of 82 dB minimum, assuming a stable controller

clock.

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Figure 88. Sinc4 Filter Response (50 SPS Output Data Rate, Zero Latency

Disabled or 12.5 SPS Output Data Rate, Zero Latency Enabled, REJ60 = 1)

SINC3 FILTER

A sinc3 filter can be used instead of the sinc4 filter. The filter is

selected using the filter bits in the filter register. This filter has good

noise performance, moderate settling time, and moderate 50 Hz

and 60 Hz (±1 Hz) rejection. In Figure 89, the blocks shown in gray

are unused.

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