Micrel

TXRX_982_R1 Evaluation Board

September 2004

M9999-092304

5

Laser Response Tuning

Overshoot/Undershoot

The damping resistors R8 and R24 installed in series

with laser are 20 . This value might be tuned to a

higher value to minimize or suppress any overshoot

or undershoot on the optical signal out of the laser,

but keep in mind that higher value damping resistors

will lead to higher rise/fall time.

Laser's Package Inductance Compensation

A compensation network comprised of C9/R26 or

C9/R31 can be used to compensate for the laser

package inductance. R26 and R31 share the same

pad on the board, so only one at a time can be

installed. The values shown on the schematic are

used for the symbol only. C9 should be a few pF and

R26/R31 around 50

.

Performance

Figure 2 shows an optical eye diagram obtained with

a Fabry Perrot laser driven differentially.

TIME (67ps/div.)

Figure 2. Optical Eye Diagram