AN1318 - APPLICATION NOTE

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3. OVERVIEW OF FAMILIES.

3.1 LVDS.

LVDS outputs always require a 100Ohm load between the differential output because they work like a

100Ohm current source of 3.2mA. This load also terminates the 50Ohm controlled impedance line.

LVDS technology is not dependent on a specific power supply, meaning that there is an easy migration

path to lower supply voltages, such as 3.3V or even 2.5V, while still maintaining the same performance.

Figure 2: LVDS Output Configuration

3.2 ECL.

This is the first differential high speed logic family ever introduced and one of today’s fastest digital

logics. However, the drawback of this technology is the negative voltage needed in relation to the actual

supply voltage commonly used. ECL outputs are open emitter outputs, requiring a DC path with a more

negative supply than VOL.

Figure 3: ECL Output Configuration

Z=50

Ω

Z=50

Ω

R=100

Ω

LVDS

LVDS

Zo

Zo

R3

ECL

ECL

VEE

R1

R2