Agilent Technologies N9010A, Руководство пользователя

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104 Chapter 14
Baseband I/Q Inputs (Option BBA) Measurement Concepts
Selecting Input Probes for Baseband Measurements
Selecting Input Probes for Baseband
Measurements
The selection of baseband measurement probe(s) and measurement
method is primarily dependent on the location of the measurement
point in the circuit. The probe must sample voltages without imposing
an inappropriate load on the circuit.
The system supports a variety of 1 M
Ω
impedance input passive probes
as well as the Agilent 1153A active differential probe using the
InfiniMax probe interface.
The Agilent 1153A active probe 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 type measurement 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 M
Ω
probes, the probe will introduce a capacitive load on
the circuit, unless a higher attenuation is used at the probe interface.
Higher attenuation helps isolate the probe, however, it 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. Many Agilent passive probes can be automatically
identified by the system, setting the input impedance 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, after
manually setting the attenuation and probe impedance configurations.
For full differential measurements, the system supports probes on each
of the four inputs. The attenuation for each of the probes should be the
same for good common mode rejection and channel match.