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Chapter 6: I/O Features in Cyclone IV Devices

High-Speed I/O Timing

Cyclone IV Device Handbook,

May 2013

Altera Corporation

Volume 1

before the next edge; this may lead to pattern-dependent jitter. With pre-emphasis, the

output current is momentarily boosted during switching to increase the output slew

rate. The overshoot produced by this extra switching current is different from the

overshoot caused by signal reflection. This overshoot happens only during switching,

and does not produce ringing.

The Quartus II software allows two settings for programmable pre-emphasis

control—0 and 1, in which 0 is pre-emphasis off and 1 is pre-emphasis on. The default

setting is 1. The amount of pre-emphasis needed depends on the amplification of the

high-frequency components along the transmission line. You must adjust the setting

to suit your designs, as pre-emphasis decreases the amplitude of the low-frequency

component of the output signal.

Figure 6–20 shows the differential output signal with pre-emphasis.

High-Speed I/O Timing

This section discusses the timing budget, waveforms, and specifications for

source-synchronous signaling in Cyclone IV devices. Timing for source-synchronous

signaling is based on skew between the data and clock signals.

High-speed differential data transmission requires timing parameters provided by IC

vendors and requires you to consider the board skew, cable skew, and clock jitter. This

section provides information about high-speed I/O standards timing parameters in

Cyclone IV devices.

Table 6–11 defines the parameters of the timing diagram shown in Figure 6–21.

Figure 6–20. The Output Signal with Pre-Emphasis

Positive channel (p)

Negative channel (n)

Overshoot

Undershoot

Table 6–11. High-Speed I/O Timing Definitions (Part 1 of 2)

Parameter

Symbol

Description

Transmitter channel-to-channel skew (1)

TCCS

The timing difference between the fastest and slowest output

edges, including tCO variation and clock skew. The clock is

included in the TCCS measurement.

Sampling window

The period of time during which the data must be valid in order for

you to capture it correctly. The setup and hold times determine

the ideal strobe position in the sampling window.

TSW = TSU + Thd + PLL jitter.

Time unit interval

TUI

The TUI is the data-bit timing budget allowed for skew,

propagation delays, and data sampling window.

Receiver input skew margin

RSKM

RSKM is defined by the total margin left after accounting for the

sampling window and TCCS. The RSKM equation is:

RSKM

TUI

SW TCCS

–

(

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