Column: JESD204 standard


Working with the JESD204B interface: What can go wrong?


By Anthony Desimone and Michael Giancioppo, Applications Engineers, Analog Devices


This is the second part to the article from the last issue J


ESD204B can be a complicated interface standard, with many operational subtleties. Finding out why it is not working requires a good


understanding of likely scenarios. Here is a guide, which is not exhaustive


but will provide a good basic baseline for those working with and wanting to learn about the JESD204B link.


1. Stuck in CGS mode: if SYNC stays at logic low level; or pulse high for <4 multiframes Checking the board, unpowered: lSYSREF and SYNC~ signalling should be DC-coupled.


lWith the board unpowered, check that 16 May 2021 www.electronicsworld.co.uk


the board SYNC~ connections from the SYNC~ source (typically from the FPGA or DAC) to the SYNC~ input (typically ADC or FPGA) are good and low impedance.


lCheck that the pull-down or pull- up resistors are not dominating the signalling, for example, if values are too small or shorted and, therefore, cannot be driven correctly.


lVerify that the differential-pairs traces (and cables, if used) of JESD204B link are matched.


lVerify that the differential impedance of the traces is 100Ω.


Checking the board, powered: lIf there is a buffer/translator in the SYNC path, make sure it is functioning properly.


lCheck that the SYNC~ source and board circuitry (both SYNC+ and SYNC−, if differential) are properly configured to produce logic levels compliant for the SYNC~ receive device. If the logic level is not compliant, then review the circuitry for the source and receive configurations to find the problem. Otherwise, consult the device manufacturer.


lCheck that the JESD204B serial transmitter and board circuitry are properly configured to produce the correct logic levels for the JESD204B serial data receiver. If the logic level is not compliant, review the circuitry of the source and receive configurations to find the problem. Otherwise, consult device the manufacturer.


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