Chapter 7: High-Speed Differential Interfaces in the Cyclone III Device Family
7–11
High-Speed I/O Standards Support
Figure 7–6 shows a RSDS, mini-LVDS, or PPDS interface with two singled-ended
output buffers and external resistors.
(1)
Figure 7–6. RSDS, Mini-LVDS, or PPDS Interface with External Resistor Network on the Top and Bottom I/O Banks
Cyclone III Device Family
Emulated RSDS,
Mini-LVDS, or PPDS
Transmitter
Resistor Network
RSDS, Mini-LVDS,
or PPDS Receiver
RS
50 Ω
50 Ω
RP
100 Ω
RS
Note to Figure 7–6:
(1) RS= 120 Ω; RP= 170 Ω
A resistor network is required to attenuate the output voltage swing to meet RSDS,
mini-LVDS, and PPDS specifications when using emulated transmitters. You can
modify the resistor network values to reduce power or improve the noise margin.
The resistor values chosen must satisfy Equation 7–1.
Equation 7–1.
RP
------
RS ×
2
------------------- = 50 Ω
RP
RS + ------
2
1
Altera recommends that you perform simulations using Cyclone III device family IBIS
models to validate that custom resistor values meet the RSDS, mini-LVDS, or PPDS
requirements.
You can use a single external resistor instead of using three resistors in the resistor
network for an RSDS interface, as shown in Figure 7–7. The external single-resistor
solution reduces the external resistor count while still achieving the required
signaling level for RSDS. However, the performance of the single-resistor solution is
lower than the performance with the three-resistor network.
December 2011 Altera Corporation
Cyclone III Device Handbook
Volume 1
ALTERA [ ALTERA CORPORATION ]
