Specifications

Innovative
Applications
Testing differential
amplifiers under
real operating
conditions
(Option 460)
Differential amplifier measurement challenges
• Conventional two-port VNAs with baluns do not provide
common-mode, differential to common-mode,
and common to differential-mode responses
• Baluns are inherently band-limited devices,
which forces multiple test setups for broad
frequency coverage
• Phase errors of baluns provide inaccurate
differential responses
• Modern four-port VNAs provide mixed-mode
S-parameter measurements with single-
ended stimulus, but differential amplifiers
may respond differently when in compression
during real operating environments
PNA-X integrated true-mode stimulus
application (iTMSA) provides:
• Mixed-mode S-parameters of differential
amplifiers driven by true differential and
common-mode signals
• Mismatch correction at the DUT input to minimize
phase errors between two sources
• Input-only drive mode that prevents damage on
amplifiers caused by stimulus on the output port
• In-fixture arbitrary phase offset and phase-offset
sweeps to optimize input matching network for
maximum amplifier gain
2
1
4
3
Differential
(180 out-of-phase)
Common
(in-phase)
Using the PNA-X’s two internal sources,
iTMSA drives the differential amplifier
under real world conditions, providing
accurate mixed-mode S-parameters
in all operating environments.
Mixed-mode S-parameters.
Without mismatch correction, the delivered signals to the DUT
will not be truly differential due to reflection from the DUT input
and the subsequent re-reflection from the sources. The reflected
signals overlay the original signals, causing phase and ampli-
tude imbalance. This effect can be corrected with mismatch
correction.
iTMSA compensates for mismatch errors by measuring the
raw matches of the VNA and DUT, and precisely adjusting the
amplitude and phase of the two signals at the reference plane
to achieve ideal true-mode signals.
Phase error
Amplitude error
DUT
mismatch
Source
mismatch
Phase after mismatch correction
Phase without mismatch correction
Frequency (Hz)
Phase Error (Deg)
24