DAC38RF82IAAV datasheet(39/147 Pages) TI2

39 / 147 page

DAC38RF82, DAC38RF89

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SLASEA6D – FEBRUARY 2017 – REVISED JUNE 2020

Product Folder Links: DAC38RF82 DAC38RF89

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8.3.10 SYSREF Capture Circuit

The JESD204B standard for Device Subclass 1 introduces a SYSREF signal that can be used as a global timing

reference to align the phase of the internal local multiframe clock (LMFC) and frame clock across multiple

devices. This allows the system to achieve deterministic latency and align data samples across several data

converters. The SYSREF signal accomplishes this goal by identifying a device clock edge for each chip that can

be used as an alignment reference. In particular, the LMFC and frame clock align to the device clock edge upon

which the SYSREF transition from “0” to “1” is sampled. SYSREF may be periodic, one-shot, or “gapped”

periodic and its period must be a multiple of the LMFC period.

Figure 30. SYSREF Signal Timing

With high-speed device clocks, the phase of the SYSREF signals relative to the device clock must meet the

setup/hold time requirements of each individual device clock. Historically, this has been done by controlling the

board-level routing delay and/or employing commercial clock distribution capable of generating device clocks and

SYSREF signals with programmable delays and with the option of splitting SYSREF into multiple SYSREFS,

each with its own fine-tuned delay. Since the DAC38RF82 (or DAC38RF89) supports device clock frequencies

up to 9 GHz, a SYSREF capture circuit is includes in the DAC38RF82 (or DAC38RF89) that allows a relaxation

in meeting the device clock setup and hold.

The SYSREF capture circuit provides:

•

tolerance to manufacturing and environmental variations in SYSREF phase

•

immunity to sampling errors due to setup/hold/meta-stability

•

information about phase of SYSREF relative to DAC clock inside the data converter

•

software compensation for phase misalignment due to PCB design errors

The concepts behind the SYSREF capture scheme are illustrated in Figure 31.

DAC38RF82IAAV Datasheet(PDF) 39 Page - Texas Instruments