At present, the trend of using jesd204b as the preferred digital interface of high-speed data converter is in full swing. The jesd204 interface was first released in 2006. It was revised to jesd204a in 2008 and to jesd204b in August 2011. Compared with previous technologies such as LVDS, this interface is superior in efficiency and has many other advantages. The design of jesd204b has the advantage of faster interface and can synchronize with the faster sampling rate of the converter. The number of package pins is reduced, which reduces the package size and shortens the routing length. The standard is applicable to both analog-to-digital converter (A / D) and digital to analog converter (D / a). Its main purpose is to serve as a general interface of field programmable gate array (FPGA) – for example, Xilinx kinex or vertex platform – but it can also be used in ASIC.

Due to the introduction of new data items and parameters, jesd204b is different from its predecessor in terms of early complexity. In this article, we will examine in depth the control characters used in the jesd204 interface. Understanding the control characters helps to deepen the understanding of link synchronization and alignment. This can help designers understand how to debug possible link problems when designing prototypes using jesd204 interface. Each control character is responsible for a different function to help maintain link data alignment and synchronization and monitor errors. If an expected character is missing or an unexpected character is received, the receiver knows that there is an error.

Its working principle is that jesd204b words are mapped into effective 8B / 10B encoded words, and set as frames and multiple frames according to specific rules. In this process, 8B / 10B coding can bring the advantage of serial data link by using control characters, which have the ability to perform various path alignment functions. 8B / 10B code mainly has five control characters, which can realize various functions for jesd204b data stream. These characters are five control characters, / K /, / F /, / A /, / R / and / Q /.

A pile of characters!

/K/ = /K28. 5 / the control character is used in the code group synchronization process through the synchronization interface (by setting! Sync). After the receiver issues the synchronization request, the transmitter starts to issue / K / = / K28 5 / character. The receiver synchronizes and waits for at least 4 consecutive / K / = / K28 5 / character. The receiver then cancels its synchronization request. This process is carried out according to the requirements of operation subclass. For subclass 0 (nondeterministic delay), the receiver receives 4 consecutive / K / = / K28 After 5 / characters, cancel the synchronization request on any frame boundary. For subclass 1 and subclass 2 (with deterministic delay, sysref or! Sync, respectively), the receiver receives four consecutive / K / = / K28 After 5 / character, cancel the synchronization request on any local multi frame clock boundary.

/A/ = /K28. 3 / control characters are used for multi frame alignment in serial data stream. The emitter inserts the end of multiple frames under specific conditions. In this case, when the last 8-bit word of the current frame at the end of multiple frames is equal to the last 8-bit word of the previous frame, the 8-bit word will be replaced by a / A / = / K28 3 / character substitution. This happens even if the last 8-bit word of the previous frame is also a control character.

/R/ = /K28. The 0 / control character is used to indicate the beginning of multiple frames. If the transmitter emits an initial channel alignment sequence, / R / = / K28 0 / will be the first non – / K28 5 / character. During the initial channel alignment sequence, the transmitter will always transmit a / R / = / K28 0 / character to indicate the beginning of multiple frames, transmitting a / A / = / K28 3 / character to indicate the end of multiple frames.

/Q/ = /K28. 4 / the control character is used in the initial path alignment sequence to prompt the receiver that the configuration data is about to start. It must be remembered that this particular control character is used only in the initial path alignment sequence and not at any other stage of data transmission.

Figure 2: / R /, / A / and / Q / control characters

/F/ = /K28. 7 / the control character is used for frame alignment in the serial data stream. This character is inserted at the end of the frame by the transmitter under specific conditions. When the last 8-bit word of the current frame (not the last 8-bit word of multiple frames) is equal to the last 8-bit word of the previous frame, the 8-bit word will be a / F / = / K28 7 / character substitution. However, if the last 8-bit word of the previous frame is a / F / = / K28 7 / character, the current 8-bit word will not be replaced.

Figure 3: / F / and / A / control characters – frame and multi frame alignment

All these control characters (/ K /, / F /, / A /, / R / and / Q /) are listed in Table 1 along with their 10 bit binary expressions. Each control character corresponds to two 10 bit binary expressions, which ensures the DC balance of data transmission and the AC coupling of the interface. This is consistent with DC balanced data in 8B / 10B data words. The scheme complies with the 8B / 10B coding specification in IEEE 802.3.

Table 1: 8B / 10B control characters

conclusion

As jesd204 becomes the preferred interface for analog-to-digital and digital to analog converters, it is necessary to understand all aspects of this technology. It is more complex than the previous interface technology. However, jesd204b does have significant advantages.

The control characters used in esd204 enable the link to be correctly synchronized and monitored for alignment. Each control character is responsible for a specific function and maintains the link between jesd204 transmitter and receiver. These control characters also provide a method for monitoring the jesd204b link and detecting errors.

With the deepening understanding of jesd204b standard, we will find many advantages of the standard, such as built-in alignment, monitoring and error detection, which shows the robustness and reliability of the standard. Jesd204b will take the latest generation of data converters into the era of higher sampling rate and smaller package size.

reference

●The JESD204B Survival Guide

● jesd204b Application Guide

●JEDEC Standard JESD204B (July 2011). JEDEC Solid State Technology AssociaTIon ()

● JEDEC standard: jesd204b (July 2011). JEDEC Solid State Technology Association

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