ProASIC3 DC and Switching Characteristics
v1.1
2 - 57
Timing Characteristics
BLVDS/M-LVDS
Bus LVDS (BLVDS) and Multipoint LVDS (M-LVDS) specifications extend the existing LVDS standard
to high-performance multipoint bus applications. Multidrop and multipoint bus configurations
may contain any combination of drivers, receivers, and transceivers. Actel LVDS drivers provide the
higher drive current required by BLVDS and M-LVDS to accommodate the loading. The drivers
require series terminations for better signal quality and to control voltage swing. Termination is
also required at both ends of the bus since the driver can be located anywhere on the bus. These
configurations can be implemented using the TRIBUF_LVDS and BIBUF_LVDS macros along with
appropriate terminations. Multipoint designs using Actel LVDS macros can achieve up to 200 MHz
with a maximum of 20 loads. A sample application is given in
Figure 2-12. The input and output
buffer delays are available in the LVDS section in
Table 2-79.
Example: For a bus consisting of 20 equidistant loads, the following terminations provide the
required differential voltage, in worst-case Industrial operating conditions, at the farthest receiver:
RS =60 Ω and RT =70 Ω, given Z0 =50 Ω (2") and Zstub =50 Ω (~1.5").
Table 2-78 AC Waveforms, Measuring Points, and Capacitive Loads
Input LOW (V)
Input HIGH (V)
Measuring Point* (V)
1.075
1.325
Cross point
Table 2-79 LVDS
Commercial-Case Conditions: TJ = 70°C, Worst-Case VCC = 1.425 V, Worst-Case VCCI = 2.3 V
Speed Grade
tDOUT
tDP
tDIN
tPY
Units
–F
0.79
2.20
0.05
1.92
ns
Std.
0.66
1.83
0.04
1.60
ns
–1
0.56
1.56
0.04
1.36
ns
–2
0.49
1.37
0.03
1.20
ns
Note: For specific junction temperature and voltage supply levels, refer to Table 2-6 on page 2-6 for derating values.
Figure 2-12 BLVDS/M-LVDS Multipoint Application Using LVDS I/O Buffers
...
R
T
R
T
BIBUF_LVDS
R
+
-
T
+
-
R
+
-
T
+
-
D
+
-
EN
Receiver
Transceiver
Receiver
Transceiver
Driver
R
S
R
S
R
S
R
S
R
S
R
S
R
S
R
S
R
S
R
S
Z
stub
Z
stub
Z
stub
Z
stub
Z
stub
Z
stub
Z
stub
Z
stub
Z
0
Z
0
Z
0
Z
0
Z
0
Z
0
Z
0
Z
0
Z
0
Z
0
Z
0
Z
0