4–12
Altera Corporation
Stratix Device Handbook, Volume 2
June 2006
Stratix & Stratix GX I/O Standards
standard and supplements the SSTL-2 standard for differential clocks.
The differential SSTL-2 standard specifies an input voltage range of
–0.3 V
≤VI ≤VCCIO + 0.3 V. The differential SSTL-2 standard does not
require an input reference voltage differential. See
Figure 4–13 for details
on differential SSTL-2 termination. Stratix and Stratix GX devices support
output clock levels for differential SSTL-2 Class II operation. The output
clock is implemented using two single-ended output buffers which are
programmed to have opposite polarity.
Figure 4–13. Differential SSTL-2 Class II Termination
LVDS - ANSI/TIA/EIA Standard ANSI/TIA/EIA-644
The LVDS I/O standard is a differential high-speed, low-voltage swing,
low-power, general-purpose I/O interface standard requiring a 3.3-V
VCCIO. This standard is used in applications requiring high-bandwidth
data transfer, backplane drivers, and clock distribution. The
ANSI/TIA/EIA-644 standard specifies LVDS transmitters and receivers
capable of operating at recommended maximum data signaling rates of
655 Mbps. However, devices can operate at slower speeds if needed, and
there is a theoretical maximum of 1.923 Gbps. Stratix and Stratix GX
devices meet the ANSI/TIA/EIA-644 standard.
Due to the low voltage swing of the LVDS I/O standard, the
electromagnetic interference (EMI) effects are much smaller than CMOS,
TTL, and PECL. This low EMI makes LVDS ideal for applications with
low EMI requirements or noise immunity requirements. The LVDS
standard does not require an input reference voltage, however, it does
require a 100
Ω termination resistor between the two signals at the input
buffer. Stratix and Stratix GX devices include an optional differential
LVDS termination resistor within the device using differential on-chip
termination. Stratix and Stratix GX devices support both input and
output levels.
Differential
Transmitter
Differential
Receiver
Z0 = 50 Ω
50
Ω
50
Ω
Z0 = 50 Ω
VTT = 1.25 V
50
Ω
50
Ω
VTT = 1.25 V
25
Ω
25
Ω