Device Design Guidelines: Agilex™ 5 FPGAs and SoCs

ID 813741
Date 4/01/2024
Public
Document Table of Contents

4.1.2.3.1. I/O Signaling Type

Table 17.  I/O Signaling Type

Number

Done?

Checklist Item

1

 

Plan the I/O signaling type based on the system requirements.

2

 

Allow the software to assign locations for the negative pin in differential pin pairs.

Agilex™ 5 devices support a wide range of industry I/O standards, including single-ended, voltage-referenced single-ended, and differential I/O standards. Follow these general guidelines when you select a signaling type.

Single-ended I/O signaling provides a simple rail-to-rail interface. Its speed is limited by the large voltage swing and noise. Single-ended I/Os do not require termination unless reflection in the system causes undesirable effects.

Voltage-referenced signaling reduces the effects of simultaneous switching outputs (SSO) from pins changing voltage levels at the same time (for example, external memory interface data and address buses). Voltage-referenced signaling also provides an improved logic transition rate with a reduced voltage swing, and minimizes noise caused by reflection with a termination requirement. However, additional termination components are required for the reference voltage source (VTT).

Differential signaling eliminates the interface performance barrier of single-ended and voltage-referenced signaling, with superior speed using an additional inverted closely coupled data pair. Differential signaling also avoids the requirement for a clean reference voltage. This is possible because of a lower swing voltage and noise immunity with a common mode noise rejection capability. Considerations for this implementation include the requirements for a dedicated PLL to generate a sampling clock, and matched trace lengths to eliminate the phase difference between an inverted and non-inverted pair.

Agilex™ 5 HSIO pins are organized in pairs to support differential standards. In your design source code, define just one pin to represent a differential pair, and make a pin assignment for this positive end of the pair. When you specify a differential I/O standard, the Quartus® Prime software automatically places the corresponding negative pin.