ProASIC3 DC and Switching Characteristics
2- 56
v1.1
Differential I/O Characteristics
Physical Implementation
Configuration of the I/O modules as a differential pair is handled by Actel Designer software when
the user instantiates a differential I/O macro in the design.
Differential I/Os can also be used in conjunction with the embedded Input Register (InReg), Output
Register (OutReg), Enable Register (EnReg), and Double Data Rate (DDR). However, there is no
support for bidirectional I/Os or tristates with the LVPECL standards.
LVDS
Low-Voltage Differential Signaling (ANSI/TIA/EIA-644) is a high-speed, differential I/O standard. It
requires that one data bit be carried through two signal lines, so two pins are needed. It also
requires external resistor termination.
The full implementation of the LVDS transmitter and receiver is shown in an example in
Figure 2-11. The building blocks of the LVDS transmitter-receiver are one transmitter macro, one
receiver macro, three board resistors at the transmitter end, and one resistor at the receiver end.
The values for the three driver resistors are different from those used in the LVPECL
implementation because the output standard specifications are different.
Along with LVDS I/O, ProASIC3 also supports Bus LVDS structure and Multipoint LVDS (M-LVDS)
configuration (up to 40 nodes).
Figure 2-11 LVDS Circuit Diagram and Board-Level Implementation
Table 2-77 Minimum and Maximum DC Input and Output Levels
DC Parameter
Description
Min.
Typ.
Max.
Units
VCCI
Supply Voltage
2.375
2.5
2.625
V
VOL
Output LOW Voltage
0.9
1.075
1.25
V
VOH
Output HIGH Voltage
1.25
1.425
1.6
V
VI
Input Voltage
0
–
2.925
V
VODIFF
Differential Output Voltage
250
350
450
mV
VOCM
Output Common-Mode Voltage
1.125
1.25
1.375
V
VICM
Input Common-Mode Voltage
0.05
1.25
2.35
V
VIDIFF
Input Differential Voltage
100
350
–
mV
Notes:
1. ± 5%
2. Differential input voltage = ±350 mV
140
Ω
100
Ω
Z0 = 50 Ω
165
Ω
165
Ω
+
–
P
N
P
N
INBUF_LVDS
OUTBUF_LVDS
FPGA
Bourns Part Number: CAT16-LV4F12