Actel Fusion Mixed-Signal FPGAs
Pr el iminar y v1 .7
2- 203
Differential I/O Characteristics
Configuration of the I/O modules as a differential pair is handled by the 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 these standards.
LVDS
Low-Voltage Differential Signal (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 2-126. 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.
Figure 2-126 LVDS Circuit Diagram and Board-Level Implementation
Table 2-165 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
Input HIGH Voltage
1.25
1.425
1.6
V
IOL
3
Input LOW Voltage
0.65
0.91
1.16
mA
IOH
3
Output HIGH Voltage
0.65
0.91
1.16
mA
VI
Input Voltage
0
2.925
V
IIL
4
Input LOW Voltage
10
μA
IIH
4
Output HIGH Voltage
10
μA
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
ZO = 50
Ω
ZO = 50
Ω
165
Ω
165
Ω
+
–
P
N
P
N
INBUF_LVDS
OUTBUF_LVDS
FPGA
Bourns Part Number: CAT16-LV4F12