Figure 16: Using An Eye Pattern To Check Modulator Polarity - Tektronix OI1125 Instruction Manual

OI1125 E/O Transmitter Instruction Manual
Data crossing point
location shifts upward
with BERT adjust
enabled and turned
fully clockwise.

Figure 16: Using an eye pattern to check modulator polarity

Take Measurements. The equipment is now set up for recording the test results in
Table 17 in the Test Record.
1. Verify that the Data Crossing Point Adjust on the BERT is turned off.
2. Verify that the eye pattern is vertically centered approximately around zero
(about a 50% duty cycle).
3. Turn on the Data Crossing Point Adjust on the BERT.
4. Turn the Data Crossing Point Adjust on the BERT to the fully clockwise
position (maximum).
The crossing point of the eye pattern will shift upward if the modulator
polarity is noninverting. This is a pass condition for the test. Record the
result in Table 17 in the Test Record.
You have now completed Table 17 in the Test Record. The remainder of Table 17
lists the specification limits for the remaining tests in these performance
verification procedures. Use the limits as a reference when filling out Tables 19
through 21 in the Test Record.
Performance Verification
Data crossing point
location with BERT
adjust turned off.
43