5

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Multi-Point Configuration

Although LVDS, as defined in the RS644 standard, does

not have the dynamic current drive to support a multi-point

bus system, there is a high drive LVDS available which has

a higher drive compared to the 3.5 mA drive of standard

LVDS. Fairchild Semiconductor works on a committee that

is addressing a new specification for high drive LVDS, or

M-LVDS (Multi-point Low Voltage Differential Signaling).

In a multi-point system, the driver can be located at any

point along the bus. For this reason, much like the multi-

drop center driven bus previously discussed, a termination

resistor is required at each end of the bus. This also means

that the driver sees the two resistors in parallel and must

supply twice the current to the bus. The 11 mA dynamic

drive is provided on the high drive version of LVDS to

address a multi-point configuration. Figure 9 gives a typical

example of a multi-point system.

FIGURE 9. Multi-Point Configuration

Conclusion

Demands for throughputs are growing exponentially and

are now exceeding several gigabits per second. Transmis-

sion of data across long media lengths demands high

speed, low noise solutions. System designers are also

always conscious of achieving high throughput while still

conserving power. LVDS, with its low swing, differential,

current driver solution, will continue to solve throughput

requirements for future generations of systems.

Fairchild does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and

Fairchild reserves the right at any time without notice to change said circuitry and specifications.

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FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT

DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD

SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or systems

which, (a) are intended for surgical implant into the

body, or (b) support or sustain life, and (c) whose failure

to perform when properly used in accordance with

instructions for use provided in the labeling, can be rea-

sonably expected to result in a significant injury to the

user.

2. A critical component in any component of a life support

device or system whose failure to perform can be rea-

sonably expected to cause the failure of the life support

device or system, or to affect its safety or effectiveness.

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