EVAL-ADN2525-NT_15 Datasheet, PDF (4/8 Pages) Analog Devices – Optical Evaluation Kit for the ADN2525

EVAL-ADN2525-NT/ADN2525-OP
QUICK START FOR OPTICAL EVALUATION
should be investigated. Less significant differences can
1. If using evaluation kit EVAL-ADN2525-NT, solder a TOSA
to the evaluation board, following soldering guidelines in
the TOSA data sheet.
2. If required, change the ALS jumper settings to obtain the
desired configuration, using Table 3.
3. Connect the evaluation board to an oscilloscope, pattern
generator, and power supplies as shown in Figure 1. A
suitable pattern generator is the Anritsu MP1763B and a
suitable oscilloscope is the Agilent 86100B with 86105C
optical plug-in. Use coaxial cables for DATAP and DATAN
of the type recommended in the General Description
section.
4. Run any applicable user calibrations on the oscilloscope
optical input.
5. Turn on the power supply (3.3 V) connected to J4. Check
that the current drawn from the 3.3 V power supply is
within the limits of the ISUPPLY specifications in the
ADN2525 data sheet.
6. Increase the voltage applied to J2 starting from 0 V until
the desired optical average power is obtained.
7. Increase the voltage applied to J1 starting from 0 V until
the desired extinction ratio is obtained.
8. To prevent damage to the TOSA, it is advisable to gradually
adjust the BSET and MSET voltages back to 0 V before
turning off the power supplies.
Using the EVAL-ADN2525-OP Evaluation Kit
sometimes be attributed to one or more of the following:
a. Dirt in the fiber connectors, optical attenuators,
or oscilloscope optical input can cause errors in
average power.
b. Optical coupling can be quite variable at the TOSA
because there is no latching mechanism for the fiber
connector. By ensuring that the connector is fully
inserted and rotating, the connector can eliminate
small discrepancies in real average power.
c. Calibration differences between the oscilloscope in the
test setup and the oscilloscope used to measure the
sample optical eye diagram can cause small
discrepancies in measured average power.
6. Confirm that the extinction ratio is close to the value
reported in the sample optical eye diagram. If the value is
significantly different, this indicates that there is a problem
with the test setup, evaluation board, or TOSA and this
should be investigated. Because the extinction ratio is a
sensitive measurement, small discrepancies can be
attributed to using different oscilloscope or optical plug-in
models or even different optical plug-ins of the same model.
7. Select the same eye mask and mask Y-alignment method as
used in the sample optical eye diagram.
8. Select the same number of waveforms for the eye diagram
capture as used in the sample optical eye diagram.
9. Confirm that the average mask margin is close to the value
reported in the sample optical eye diagram. If the value is
When using the EVAL-ADN2525-OP evaluation kit, it is
recommended that the kit be initially set up to reproduce the
sample optical eye diagram that is included with the kit. This
confirms that the test setup is configured correctly to produce a
high quality optical eye diagram. The following steps should be
followed to reproduce the sample optical eye diagram:
1. Set up the board following the recommendations in the
Quick Start for Optical Evaluation section.
2. Adjust the data rate and pattern to the settings used in the
sample optical eye diagram and select the appropriate
optical filter and wavelength on the oscilloscope.
3. Adjust the BSET and MSET voltages to the settings used in
the sample optical eye diagram.
4. Confirm that the VCC supply current (ICC) and the
IBMON voltage at TP1 are close to the values reported in
the sample optical eye diagram. If either of the values is
significantly different, this indicates that there is a problem
with the test setup, evaluation board, or TOSA, and this
should be investigated.
5. Confirm that the real average power is close to the value
reported in the sample optical eye diagram. The real
average power is the average power as measured by the test
equipment plus the measured attenuation of any optical
attenuators in the optical signal path. If the value is
significantly different, this indicates that there is a problem
with the test setup, evaluation board, or TOSA, and this
significantly different, this indicates that there is a problem
with the test setup, evaluation board, or TOSA and this
should be investigated. Differences can be attributed to one
or more of the following:
a. A poor quality differential electrical eye diagram at
the output of the coaxial cables from the pattern
generator results in a poor optical eye diagram.
Measuring the electrical eye diagram on these signals
confirms or eliminates this possibility. Delay skew
>2 ps between the DATAP and DATAN signals is one
example of a degraded input signal that leads to a
degraded optical eye diagram.
b. Small discrepancies can be attributed to using
different oscilloscope or optical plug-in models or
even different optical plug-ins of the same model.
Different optical plug-in models have different
bandwidths, noise, and time-base jitter and this can
affect eye mask margin. Different optical plug-ins of
the same model can have different frequency
responses in the optical filter that is within the
allowed tolerance and this can affect eye mask margin.
c. If an optical attenuator is required to keep the eye
diagram within the oscilloscope range, an attenuation
value should be chosen that keeps the optical signal in
the upper end of the oscilloscope range. Otherwise,
the effect of oscilloscope noise on the eye mask
margin is increased.
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