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Reference
GB1400 User Manual 3-25
AUTO SEARCH parameter. Therefore, you should normally turn off AUTO
SEARCH if you want to fix delay at a specific value.
Input Termination
The input termination can be independently selected for the CLOCK, DATA, and
REF DATA inputs. Note that the termination selected for CLOCK and DATA
also applies to the CLOCK-BAR and DATA-BAR inputs. Available input
terminations are shown in table below.
Table 3-7. Input Terminations for CLOCK, DATA, and REF DATA
Label Termination
GND 50 Ohms to ground.
- 2 V 50 Ohms to -2 VDC.
AC
50 Ohms, via 0.01 µF capacitor, to ground.
Procedure for Selecting Input Termination
1. Select the DATA, CLOCK, or REF DATA inputs using the F2 and F3 keys.
2. Press the TERM key. Verify that its LED turns on.
3. Press the input up/down keys while observing the selected termination in the
display. Available terminations are: GND, -2V, and AC.
The displayed termination becomes effective immediately. In other words,
termination is changed each time you press the up or down key.
Low-Frequency Effects of AC Termination on Single-ended
Operation
Because the single-ended AC termination is AC-coupled to ground, input
impedance will deviate from the nominal 50 Ohm value at low frequencies. As a
practical matter, for any PRBS pattern analyzed by the GB1400, frequency
effects will not be noticed until the peak energy frequency is less than about 10
MHz, which for PRBS patterns will occur only when bit rate is less than about 20
Mb/s. However, for WORD patterns with long strings of contiguous zeros,
effects may be noticed at higher bit rates.
Note that when the AC termination is used with differential operation, the input
termination is not "AC-coupled". Therefore, the above low-frequency limit on
use of the AC termination does not apply when operating the CLOCK or DATA
inputs in the differential mode. Specifically, when the Analyzer clock or data
inputs are set up for differential operation, the AC termination may be used over
the entire bit rate operating range of the Analyzer.