Micrel, Inc.

SY89473U

May 2007

10

M9999-052207-B

LVPECL Output Interface Applications

LVPECL has a high input impedance, a very low

output impedance (open emitter), and a small signal

swing which results in low EMI. LVPECL is ideal for

driving

50Ω-

and-100Ω-controlled

impedance

transmission lines. There are several techniques for

terminating the LVPECL output including: Parallel

Termination-Thevenin

Equivalent,

Parallel

Termination

(3-resistor),

and

AC-coupled

Termination. Unused output pairs may be left

floating. However, single-ended outputs must be

terminated, or balanced.

Note:

1.

For +2.5V systems, R1 = 250Ω, R2 = 62.5Ω.

Figure 4a. Parallel Termination-Thevenin Equivalent

Note:

1.

Power-saving alternative to Thevenin termination.

2.

Place termination resistors as close to destination inputs as

possible.

3.

4.

For 2.5V systems, Rb = 19Ω.

Figure 4b. Parallel Termination (3-Resistor)

Related Product and Support Information

Part Number

Function

Data Sheet Link

SY89474U

Precision LVDS 2:1 Multiplexer with

1:2 Fanout and Internal Termination

www.micrel.com/product-info/products/sy89474u.shtml

SY89475U

Precision CML 2:1 Multiplexer with

1:2 Fanout and Internal Termination

www.micrel.com/product-info/products/sy89475u.shtml

HBW

Solutions

New Products and Applications

www.micrel.com/product-info/products/solutions.shtml