PROASIC3E datasheet(14/37 Pages) ACTEL

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I/O Structures in IGLOOe and ProASIC3E Devices

v1.4

B-LVDS/M-LVDS

Bus LVDS (B-LVDS) refers to bus interface circuits based on LVDS technology. Multipoint LVDS

(M-LVDS) specifications extend the 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 B-LVDS

and M-LVDS to accommodate the loading. The driver requires 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

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 9. The input and output buffer delays are available in the LVDS

sections in the datasheet.

Example: For a bus consisting of 20 equidistant loads, the terminations given in EQ 1 provide the

required differential voltage, in worst case industrial operating conditions, at the farthest receiver:

RS =60 Ω, RT = 70 Ω, given ZO = 50 Ω (2") and Zstub = 50 Ω (~1.5").

EQ 1

Figure 9 • A B-LVDS/M-LVDS Multipoint Application Using LVDS I/O Buffers

...

BIBUF_LVDS

Receiver

Zstub

Transceiver

Receiver

Transceiver

Driver

Zstub Zstub

Zstub

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