Agilent Technologies X Series Manual page 415

Input/Output
For full differential measurements, the system supports probes on each of the four inputs. The
attenuation of the probes should be the same for good common mode rejection and channel match.
Both active and passive probes in single ended and differential configurations can be calibrated. This
calibration uses the Cal Out BNC connection and a probe connection accessory. The calibration achieves
excellent absolute gain flatness in a probed measurement. It matches both the gain and frequency
response of the I and Q channels as well as any delay skew, resulting in high accuracy in derived
measurements such as Error Vector Magnitude (EVM).
When a probe is connected a status message will be displayed. The message will indicate if calibration
data is available or not. Calibration data is saved for each type of probe (including "none") for each port
and will be reapplied whenever that type of probe is re-connected to the same port. For probes with
EEPROM identification, the calibration data will be stored based on the unique probe identifier and will
reapply data for that particular probe if it is available. The data will not follow a probe from one port to
another. For probes without EEPROM identification, the instrument cannot distinguish between different
probes of the same type and it will use the data from the last calibration for that probe type on that port.
When in differential mode, both the main and complementary probes are expected to be of the same
type.
In some situations, the I and Q channels should be configured identically. In other situations it is
convenient to control them independently. Some menus have a "Q Same as I" setting that will cause the
Q channel configuration to mirror the I channel configuration, avoiding the overhead of double data
entry when the channels should be the same.
The output port is for calibrating the I/Q input ports, although it can also be manually controlled.
There are two types of calibrations available: cable calibration and probe calibration. The cable
calibration will guide the user through connecting each input port in turn. All ports must be calibrated
together. The probe calibration is done for a specific channel (I or Q). If in Single-Ended mode, only the
main port is calibrated. When in Differential Input mode, the user is guided through calibrating both
main and complementary ports.
The front panel I/Q port LEDs indicate the current state of that port. On (green) indicates it is active, and
off (dark) indicates it is not in use. For example, the Cal Out port LED is on if and only if there is signal
coming out of that port.
The input is a context and some parameters have separate values for each context. The SCPI for these
parameters has an optional "[:RF|IQ]" node. If the specific context is omitted, the command acts on the
current input context's value. Here are the parameters that are input context sensitive:
• Center Frequency
• Trigger Source
It is important to distinguish between the I and Q input ports and the displayed I and Q data values. The I
and Q input ports feed into a digital receiver that does digital tuning and filtering. The I and Q data seen
by the user (either on the display or through SCPI) corresponds to the real ("I") and the imaginary ("Q")
output from the digital receiver. When the input path is I+jQ or I Only and the center frequency is 0 Hz
the I input ends up in as the real output from the receiver and appears as "I" data. Likewise, when the
input path is I+jQ and the center frequency is 0 Hz, the Q input ends up as the imaginary output from the
receiver and appears as "Q" data. However, when the input path is Q Only, the Q input is sent to the
receiver as Q+j0, so the receiver output has the Q input coming out on the real output, and so in Q Only,
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