Stratix II and Stratix II GX I/O Standards Support
Figure 4–13. Differential SSTL-18 Class II Termination
VTT = 0.9 V
VTT = 0.9 V
VTT = 0.9 V
VTT = 0.9 V
Differential
Transmitter
Differential
Receiver
50 Ω
25 Ω
50 Ω
50 Ω
50 Ω
Z
= 50 Ω
0
25 Ω
Z
= 50 Ω
0
1.8-V Differential HSTL Class I and 1.8-V Differential HSTL Class II
The 1.8-V differential HSTL specification is the same as the 1.8-V
single-ended HSTL specification. It is used for applications designed to
operate in the 0.0- to 1.8-V HSTL logic switching range such as QDR
memory clock interfaces. Stratix II and Stratix II GX devices support both
input and output levels operation. Figures 4–14 and 4–15 show details on
1.8-V differential HSTL termination.
Stratix II and Stratix II GX devices support 1.8-V differential HSTL I/O
standards in pseudo-differential mode, which is implemented by using
two 1.8-V HSTL single-ended buffers.
The Quartus II software only supports pseudo-differential standards on
the INCLK, FBINand EXTCLKports of enhanced PLL, as well as on DQS
pins when DQS megafunction (ALTDQS, Bidirectional Data Strobe) is
used. Two single-ended output buffers are automatically programmed to
have opposite polarity so as to implement a pseudo-differential output. A
proper VREF voltage is required for the two single-ended input buffers to
implement a pseudo-differential input. In this case, only the positive
polarity input is used in the speed path while the negative input is not
connected internally. In other words, only the non-inverted pin is
required to be specified in your design, while the Quartus II software
automatically generates the inverted pin for you.
Although the Quartus II software does not support 1.8-V
pseudo-differential HSTL I/O standards on left/right I/O banks, you can
implement these standards at these banks. You need to create two pins in
the designs and configure the pins with single-ended 1.8-V HSTL
standards. However, this is limited only to pins that support the
differential pin-pair I/O function and is dependent on the single-ended
1.8-V HSTL standards support at these banks.
4–14
Stratix II Device Handbook, Volume 2
Altera Corporation
January 2008
ALTERA [ ALTERA CORPORATION ]
