AFE4403 datasheet(32/85 Pages) TI2

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ADC_RDY

ADC Conversion of

(LED2-Ambient2)

Data 5

Data 6

Data 7

Data 8

Data 9

Data 10

Data 11

Data 12

Data 4

Average of Data 5, 6, 7, 8

Average of Data 1, 2, 3, 4

25-Hz Frequency

PRF Setting,

100 Hz

LED On

Data 5

Data 6

Data 7

Data 8

Data 9

Data 10

Data 11

Data 12

Data 4

AFE4404

SBAS689D – JUNE 2015 – REVISED DECEMBER 2016

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8.4.6 Decimation Mode

The AFE4404 has a decimation mode that can be used to improve the performance at low pulse repetition

frequencies (PRFs). In this mode, up to N (N = 2, 4, 8, or 16) consecutive data samples can be averaged. The

averaged output comes out one time every N clock cycles. The ADC_RDY frequency also reduces to PRF / N.

A timing diagram is shown in Figure 37 for where the decimation factor = 4 and PRF = 100 Hz. Figure 37 is only

intended to illustrate the change in periodicity of ADC_RDY and the update rate of the registers relative to the

pulse repetition period. However, the timing of all other signals continues to be as per the descriptions mentioned

in the Timing Engine section.

Figure 37. Decimation Mode Enabled Timing Diagram

(Decimation Factor = 4, PRF = 100 Hz)

8.4.6.1 Decimation Mode Power and Performance

The main advantage of the decimation mode is that this mode can be used to reduce the readout rate of the

MCU because the data rate reduces by the decimation factor. Normally, reducing the data rate leads to SNR

loss. However, with decimation mode, there is no SNR loss regardless of the lower data rate because of the

averaging of consecutive samples. Table 15 compares different modes of operation.

Table 15. Different Modes of Operation

MODE

RATE OF DEVICE SAMPLES

AND CONVERSIONS

RATE OF MCU DATA READS

RELATIVE PERFORMANCE

No decimation, 100-Hz PRF

100 Hz

Reference

No decimation, 25-Hz PRF

25 Hz

SNR is approximately 6 dB lower

than reference

4X decimation mode,

100-Hz PRF

100 Hz

25 Hz

SNR is comparable to reference

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