Tektronix 071-0590-00 user manual Input Terminations for CLOCK, DATA, and REF Data

Reference

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.

GB1400 User Manual 3-25