Keysight x-series User Reference Manual page 158

4 Input/Output Functions
Input/Output
The Agilent 113x Series active probes can be used for both single ended and differential measurements. In
either case a single connection is made for each channel (on either the I or Q input). The input is
automatically configured to 50 Ω single ended and the probe power is supplied through the Infinimax
interface. The probe can be configured for a variety of input coupling and low frequency rejection modes. In
addition, a wide range of offset voltages and probe attenuation accessories are supported at the probe
interface. The active probe has the advantage that it does not significantly load the circuit under test, even
with unity gain probing.
With passive 1 MΩ probes, the probe will introduce a capacitive load on the circuit, unless higher
attenuation is used at the probe interface. Higher attenuation reduces the signal level and degrades the
signal-to-noise-ratio of the measurement. Passive probes are available with a variety of attenuation
values for a moderate cost. Most Agilent passive probes can be automatically identified by the system,
setting the input impedance setting required as well as the nominal attenuation. For single ended
measurements a single probe is used for each channel. Other passive probes can be used, with the
attenuation and impedance settings configured manually.
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.
158 EMI Receiver Mode Reference