Overcoming Design Challenges - Implementing High Performance Interfaces

Abstract

Today’s complex systems have devices operating at multiple voltage nodes that require high-bandwidth, fast-transitions with low-delay. Texas Instruments' TXV family offers options from both the fixed-directional and the general-purpose direction-controlled translation portfolios with the flexibility for high-bandwidth, while avoiding unexpected high and low logic performance issues for applications that can have timing-margin sensitive interfaces. This application note focuses on demonstrating key timing benefits of the TXV family for strict timing applications, using TXV-EVMs.

The application note further describes using the TXV Voltage Translators and Level Shifters versus competitor, for systems with strict timing requirements; such as Reduced Gigabit Media Independent (RGMII) applications.

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1 Introduction

RGMII as an example of a high-bandwidth data bus protocol typically communicates with very stringent timing considerations, interfaced between Ethernet Modules such as Media Access Control devices (MAC) / Microcontroller unit (MCU) and Ethernet Physical Layers (PHYs) as shown in Figure 1-2, with aggregate bandwidth as high as 1000Mbps.

RGMII as a communication protocol can be found in many applications that sends data over Ethernet, widely used in industrial, telecommunication and automotive sectors. Figure 1-1 illustrates typical example for transferring data over Ethernet using RGMII. Once all video and audio data are processed, the video and audio data are sent from the MAC or MCU to the PHY where they are serialized and sent over Ethernet.

TXV level shifters are used to bridge voltage mismatch, enabling communication, and further supporting the required timing considerations in RGMII applications.

Figure 1-1 Automotive Example for Data Over Ethernet Using RGMII

Table 3-5 highlights RGMII timing considerations. For more information, see Supporting Time and Skew Sensitive Interfaces with TI's TXV Level-Shifter Portfolio, application brief.

Table 1-1 RGMII 2.0 Timing Budget

Parameter	Min	Typical	Max	Units
Output Skew	-500	0	500	ps
Duty Cycle	45	50	55	%
Data Rate (Gigabit operation)		125		MHz
Rise / Fall time (20-80%)			750	ps

Figure 1-2 TXV0108 Typical Application