User`s guide

Chapter 11 207
Peripheral Devices
N5102A Digital Signal Interface Module
Clock Source
The clock signal for the N5102A module is provided in one of three ways through the following
selections:
• Internal: generated internally in the interface module (requires an external reference)
•External: generated externally through the Ext Clock In connector
•Device: generated externally through the Device Interface connector
The clock source is selected using the N5102A module UI on the signal generator, as shown in
Figure 11- 2.
Figure 11-2 Clock Source Selection
When you select a clock source, you must let the N5102A module know the frequency of the clock
signal using the
Clock Rate softkey. In the internal clock source mode, use this softkey to set the
internal clock rate. For device and external clock sources, this softkey must reflect the frequency of
the applied clock signal.
When the clock source is Internal, a frequency reference must be applied to the Freq Ref connector.
The frequency of this applied signal needs to be specified using the
Reference Frequency softkey, unless
the current setting matches that of the applied signal.
The selected clock source provides the interface module output clock signal at the Clock Out and the
Device Interface connectors.
Common Frequency Reference
The clocking flexibility of the digital signal interface module allows the setting of arbitrary clock rates
for the device under test. In general, the clock rate inside the PSG will be different from the interface
module clock rate, so the interface module performs a rate conversion. An important aspect of this
conversion is to have accurate clock rate information to avoid losing data. The module relies on
relative clock accuracy, instead of absolute accuracy, that must be ensured by using a single
frequency reference for all clock rates involved in the test setup. This can be implemented in various
ways (see the five drawings in Figure 11- 3 on page 209), but whatever way it is implemented, the
External and Device selection:
Set to match the clock rate
of the applied clock signal
Internal selection: Set the
internal clock rate
Internal clock source
selection: Set the frequency
of the applied reference
signal.