User Manual 3153
Using The Instrument 3-51
Using the SCLK
Dividers
Channels 2 and 3 have Sample Clock dividers. The main usage of these
dividers is in synchronized mode, when channel 1 provides the master
clock and channel 2 and 3 divide this clock using their sample clock
dividers. Note that the sample clock divider can accept integer values
only from 1 through 64k.
The dividers are active at all times. Upon power up, the SCLK dividers
are set to 1. Changing the dividing ratio from 1 to another number
modifies the sample clock from the value of the active sample clock to
the sample clock divided by the clock divider value. For example, if
channel 2’s active sample clock is 10 MSa/s and the clock divider is set
to 5, the resultant sample clock frequency will be 2 MSa/s.
Sample clock dividers affect the channel’s sample clock regardless of
whether the sample clock source is internal, external or coupled from the
master channel.
Use the following command to program the sample clock divider:
FREQuency:RASTer:DIVider <integer>
Note that only integer numbers ranging from 1 through 64k can be used
as sample clock dividers. If a floating point number is specified as a
parameter then an error will occur.
The query:
FREQuency:RASTer:DIVider?
queries the sample clock divider and returns an integer number.
Adjusting Phase
Between Channels
Channel synchronization controls the start phase such that all channels
start generating waveforms at the same instance, regardless of
waveform shape and frequency settings.
In general, the initial start phase offset is around 0
°
. However, due to
variations in propagation delays, there is an unavoidable (but minimal)
skew between the channels. The initial skew between channels is
specified in Appendix A.
There are no internal provisions to correct skew between channels.
However, phase skew can be corrected by adjusting the length of cable
connected to the output connectors. One meter of 50
Ω
coax cable
amounts to about 2 ns of delay time. Use this general guideline to adjust
the skew for your system. For example, if channel 2 lags channel 3 by
1.2 ns, delay the output of channel 3 by 1.2 ns. The output cable for
channel 3 should be made roughly 0.6 meters longer than that of
channel 1 to compensate for this skew.
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