AD9625 datasheet(48/74 Pages) AD

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AD9625

Data Sheet

Rev. C | Page 46 of 72

CLK+

SYSREF–

SYSREF+

CLK–

HOLD IRQ ERROR

Figure 97. SYSREF± Edge Falls Within the Actual Hold Time Window and

Triggers an IRQ Error

IRQ Guardband Delays (SYSREF± Setup and Hold)

Additional guardband delays can be added to each of the default

setup and hold time windows. This yields more information to

the system about the placement of the SYSREF± edge within the

clock period and help identify the proximity of the SYSREF± edge

to the actual setup and hold time windows. With a default

setting of 00b for both setup and hold, each has seven

additional settings to increase the guardband timing feedback

information.

There are 3 bits that define the SYSREF± setup time guardband

located in Register 0x13C[7:5]. There are 3 bits that define the

SYSREF± hold time guardband located in Register 0x13B[7:5].

A setting of 000b for either is the default of no additional timing

guardband, with just the actual setup and hold time window

used as the IRQ.

The IRQ flag for the SYSREF± setup window is in Register

0x100[2], while the IRQ flag for the SYSREF± hold window is

in Register 0x100[3]. The IRQ flag mask for the SYSREF± setup

window is in Register 0x101[2], while the IRQ flag mask for the

SYSREF± hold window is in Register 0x101[3].

After each IRQ alert, the status needs to be cleared, as it does

not automatically clear itself, even if the alert conditions are no

longer valid. For either the SYSREF± setup or hold IRQ alert,

the status is cleared using Register 0x03A[6]. Setting Register

0x03A[6] = 1 clears and hold the IRQ in a reset value of 0. To

allow IRQ flags pertaining to SYSREF± again, set Register

0x03A[6] = 0.

CLK+

SYSREF–

SYSREF+

CLK–

SETUP AND

GUARDBAND TIME

HOLD AND

GUARDBAND TIME

SETUP GUARDBAND

IRQ DELAYS

HOLD GUARDBAND

IRQ DELAYS

Figure 98. SYSREF± Edge Falls Within the Guardbanded Setup Time Window

and Triggers an IRQ Error

In Figure 98, the SYSREF± edge meets the default setup and

hold time of the clock, but would trigger an IRQ event only if

certain setup time guardband delays were used. For this figure,

all of the setup guardband delays that would place the SYSREF±

crossing edge between it and the dotted black line would incur

an IRQ event equal to 1. All other settings would be 0. Because

there is no edge in the hold guardband delays, those would all

be 0 if they were set.

Table 21. IRQ Outcomes for All Setup or Hold Guardband

Settings for the Case in Figure 98

Setting/IRQ

Setup

Hold

000

001

010

011

100

101

110

111

CLK+

SYSREF–

SYSREF+

CLK–

SETUP AND

GUARDBAND TIME

HOLD AND

GUARDBAND TIME

SETUP GUARDBAND

IRQ DELAYS

HOLD GUARDBAND

IRQ DELAYS

Figure 99. SYSREF± Edge Falls Within the Guardbanded Hold Time Window

and Triggers an IRQ Error

In Figure 99, the SYSREF± edge misses the default setup and

hold time of the clock, but would trigger an IRQ event only if

certain hold time guardband delays were used. For this figure,

all of the hold guardband delays that would place the SYSREF±

crossing edge between it and the dotted black line would incur

an IRQ event equal to 1. All other settings would be 0. Because

there is no edge in the setup guardband delays, those would all

be 0 if they were set.

Table 22. IRQ Outcomes for All Setup or Hold Guardband

Settings Using the Case in Figure 99

Setting/IRQ

Setup

Hold

000

001

010

011

100

101

110

111

AD9625 Datasheet(PDF) 48 Page - Analog Devices

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