0

0.4

0.8

1.2

1.6

2

2.4

2.8

3.2

3.6

4

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

D001

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

D001

18

PCM1840

SBAS989 – APRIL 2019

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Product Folder Links: PCM1840

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Copyright © 2019, Texas Instruments Incorporated

7.3.7.2 Configurable Digital Decimation Filters

The device record channel includes a high dynamic range, built-in digital decimation filter to process the

oversampled data from the multibit delta-sigma (ΔΣ) modulator to generate digital data at the same Nyquist

sampling rate as the FSYNC rate. The decimation filter can be chosen from two different types only in slave

mode, depending on the required frequency response, group delay, and phase linearity requirements for the

target application. The selection of the decimation filter option can be done by the MD0 pin. Table 7 shows the

decimation filter mode selection for the record channel.

Table 7. Decimation Filter Mode Selection for the Record Channel

MD0

DECIMATION FILTER MODE SELECTION (Supported Only in Slave Mode)

LOW

Linear phase filters are used for the decimation in slave mode. For master mode, the device

always use linear phase filters for the decimation.

HIGH

Low latency filters are used for the decimation in slave mode. For master mode, the device

always use linear phase filters for the decimation.

7.3.7.2.1

Linear Phase Filters

The linear phase decimation filters are the default filters set by the device and can be used for all applications

that require a perfect linear phase with zero-phase deviation within the pass-band specification of the filter. The

filter performance specifications and various plots for all supported output sampling rates are listed in this

section.

7.3.7.2.1.1

Sampling Rate: 8 kHz or 7.35 kHz

Figure 24 and Figure 25 respectively show the magnitude response and the pass-band ripple for a decimation

filter with a sampling rate of 8 kHz or 7.35 kHz. Table 8 lists the specifications for a decimation filter with an

8-kHz or 7.35-kHz sampling rate.

Figure 24. Linear Phase Decimation Filter Magnitude

Response

Figure 25. Linear Phase Decimation Filter Pass-Band

Ripple

Table 8. Linear Phase Decimation Filter Specifications

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Pass-band ripple

–0.05

0.05

dB

Stop-band attenuation

72.7

dB

81.2

Group delay or latency

17.1