ADS5294IPFPR datasheet(54/82 Pages) TI2

54 / 82 page

H(f)

Set 1

Set 2

0.2*Fs

0.3*Fs

0.2*Fs

0.3*Fs

0.5*Fs

Set 4

Set 3

H(f)

0.1*Fs

0.15*Fs

0.075*Fs

0.125*Fs

0.225*Fs

0.275*Fs

Set 6

Set 5

H(f)

0.275*Fs

0.225*Fs

0.375*Fs

0.4*Fs 0.5*Fs f

0.35*Fs

ADS5294

SLAS776E – NOVEMBER 2011 – REVISED APRIL 2018

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A decimation filter can be introduced at the output of each channel. To enable this feature, the

GLOBAL_EN_FILTER should be set to ‘1’. Setting this bit to ‘1’ increases the overall latency of each channel to

20 clock cycles irrespective of whether the filter for that particular channel has been chosen or not (using the

USE_FILTER bit). The bits marked FILTERn_COEFF_SET<2:0>, FILTERn_RATE<2:0>, ODD_TAPn and

USE_FILTERn represent the controls for the filter for Channel n. Note that these bits are functional only when

the GLOBAL_EN_FILTER gets set to '1' and USE_FILTERn bit is set to '1'. For illustration, the controls for

channel 1 are listed in Table 17:

The USE_FILTER1 bit determines whether the filter for Channel 1 is used or not. When this bit is set to ‘1’, the

filter for channel 1 is enabled. When this bit is set to ‘0’, the filter for channel 1 is disabled but the channel data

passes through a dummy delay so that the overall latency of channel 1 is 20 clock cycles. With the

USE_FILTER1 bit set to ‘1’, the characteristics of the filter can be set by using the other sets of bits.

The ADS5294 has six sets of filter coefficients stored in memory. Each of these sets define a unique pass band

in the frequency domain and contain 12 coefficients (each coefficient is 12-bit long). These 12 coefficients are

used to implement either a symmetric 24-tap (even-tap) filter, or a symmetric 23-tap (odd-tap) filter. Setting the

Channel 1. The bits FILTER1_COEFF_SET<2:0> are used to choose the required set of coefficients for Channel

The passbands corresponding to of each of these filter coefficient sets is shown in Figure 56

Figure 56. Filter Types

Coefficient Sets 1 and 2 are the most appropriate when decimation by a factor of 2 is required, whereas

Coefficient Sets 3, 4, 5, and 6 are appropriate when decimation by a factor of 4 is desired. The computation rate

of the filter output is set independently using the bits FILTERn_RATE<2:0>. The settings are shown in Table 17.

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