Micrel
TXRX_982_R1 Evaluation Board
Laser Response Tuning
Performance
Figure 2 shows an optical eye diagram obtained with
a Fabry Perrot laser driven differentially.
Overshoot/Undershoot
The damping resistors R8 and R24 installed in series
with laser are 20ꢀ. 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.
(2.5Gbps), PRBS 223–1, ER = 9.5
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 ꢀ.
TIME (67ps/div.)
Figure 2. Optical Eye Diagram
5
September 2004
M9999-092304
hbwhelp@micrel.com or (408) 955-1690
MICREL [ MICREL SEMICONDUCTOR ]
