ProASIC3 DC and Switching Characteristics
2-66
Revision 13
B-LVDS/M-LVDS
Bus LVDS (B-LVDS) 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. Microsemi LVDS drivers provide the higher drive
current required by B-LVDS 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 Microsemi 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
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 and
RT =70 , given Z0 =50 (2") and Zstub =50 (~1.5").
LVPECL
Low-Voltage Positive Emitter-Coupled Logic (LVPECL) is another differential I/O standard. It requires
that one data bit be carried through two signal lines. Like LVDS, 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 2-13. The
building blocks of the LVPECL 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 LVDS implementation because the output standard
specifications are different.
Figure 2-12 B-LVDS/M-LVDS Multipoint Application Using LVDS I/O Buffers
...
RT
BIBUF_LVDS
R
+
-
T
+
-
R
+
-
T
+
-
D
+
-
EN
Receiver
Transceiver
Receiver
Transceiver
Driver
RS RS
Zstub
Z0
Figure 2-13 LVPECL Circuit Diagram and Board-Level Implementation
187 W
100
Z0 = 50
100
100
+
–
P
N
P
N
INBUF_LVPECL
OUTBUF_LVPECL
FPGA
Bourns Part Number: CAT16-PC4F12