ADC3641 datasheet(34/77 Pages) TI

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Normalized Frequency (Fs)

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

-120

-100

-80

-60

-40

-20

Decb

Passband

Transition Band

Alias Band

Attn Spec

Figure 8-30. Decimation by 16 complex frequency

response

Normalized Frequency (Fs)

0.003

0.006

0.009

0.012

0.015

0.018

0.021

0.024

0.027

0.03

-0.2

-0.19

-0.18

-0.17

-0.16

-0.15

-0.14

-0.13

-0.12

-0.11

-0.1

Decb

Passband

Transition Band

Alias Band

Attn Spec

Figure 8-31. Decimation by 16 complex passband

ripple response

Normalized Frequency (Fs)

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

-120

-100

-80

-60

-40

-20

Decb

Passband

Transition Band

Alias Band

Attn Spec

Figure 8-32. Decimation by 32 complex frequency

response

Normalized Frequency (Fs)

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

-0.25

-0.245

-0.24

-0.235

-0.23

-0.225

-0.22

-0.215

-0.21

-0.205

-0.2

Decb

Passband

Transition Band

Alias Band

Attn Spec

Figure 8-33. Decimation by 32 complex passband

ripple response

8.3.4.5 SYNC

The PDN/SYNC pin can be used to synchronize multiple devices using an external SYNC signal. The PDN/

SYNC pin can be configured via SPI (SYNC EN bit) from power down to synchronization functionality and is

latched in by the rising edge of the sampling clock as shown in Figure 8-34.

CLK

tS,SYNC

tH,SYNC

SYNC

Figure 8-34. External SYNC timing diagram

The synchronization signal is only required when using the decimation filter - either using the SPI SYNC register

or the PDN/SYNC pin. It resets internal clock dividers used in the decimation filter and aligns the internal clocks

as well as I and Q data within the same sample. If no SYNC signal is given the internal clock dividers will not be

synchronized, which can lead to a fractional delay across different devices. The SYNC signal also resets the

NCO phase and loads the new NCO frequency (same as the MIXER RESTART bit).

When trying to resynchronize during operation, the SYNC toggle should occur at 64*K clock cycles, where K is

an integer. This ensures phase continuity of the clock divider.

ADC3643

SBAS886 – OCTOBER 2020

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