Active load pull system
View Patent ↗A calibration and impedance synthesis (tuning) method for active load pull systems employs prior calibration and dynamic interpolation routines. Since active load pull systems differ from passive load pull systems in that the device under test (DUT) is part of the tuner, in large signal the tuner cannot be calibrated independently. The new active load pull system comprises an impedance generation algorithm based on prior calibration and dynamic in memory interpolation routines. At small signal levels the procedure is like with passive load pull tuners. At higher power, where the DUT becomes nonlinear, the calibration yields only approximate data. For load pull contour generation this is still adequate.
1. A calibration method for an active load pull system, which includes:
a device under test (DUT), a first vector signal generator (VSG #1) injecting radio frequency (RF) power P1 into an input port #1 of the DUT, a second vector signal generator (VSG #2) injecting RF power P2 into an output port #2 of the DUT, and measurement capability of the RF signal power waves entering (<a1>,<a2>) into the input and departing (<b1>,<b2>) from the output port of the DUT,
comprising the following steps:
a) a setup step:
install and bias the device under test (DUT);
define a multitude of M frequencies Fi, with 1≤i≤M,
define a minimum and a maximum input power supplied by the first VSG #1;
and,
b) a scaling step:
set a medium frequency F=F1+(FM−F1)/2;
determine a center signal phase Pc of the second VSG #2 as follows:
set the input signal power of the first VSG #1 to create a substantial |<b2>|;
set the signal power P2 of the second VSG #2 to create |<a2>|≈|<b2>|;
and,
in a phase control loop:
increase phase Φ2 of the second VSG #2 in 10-degree increments from 0 to 360 degrees, measure Γ=|<a2>|/|<b2>| and select Φc-Φ2 for maximum Γ;
set Φ2-Φc;
and,
in a scaling process:
increase the input power of the first VSG #1 from the minimum to the maximum value in approximately 10 equal increments, and, for each input power P1 setting, measure the departing signal |<b2>| and set the signal power P2 of the second VSG #2 to create entering signal |<a2>| approximately equal to |<b2>| and save a ratio A (F, P1,|<b2>|)=P2/P1;
and,
c) in a calibration pattern measurement process:
for each frequency of the multitude M of frequencies Fi:
step through the input power P1 settings of the scaling process and set P2=A(Fi)*P1,
and, for each input power P1 setting:
step through the phase Φ2 of the second VSG #2 from 0 to 360 degrees in 10-degree increments,
measure Gamma=<b2>/<a2> and save in a calibration file CF in a format (Fi, P1, P2, Φ2, Gamma).
2. A load pull measurement process performed using the active load pull system of claim 1 comprising:
select an input power P1,
select a reflection factor segment of the Smith chart for each frequency Fi;
retrieve P1, P2, Φ2 and Gamma data from the calibration file CF into dynamic computer memory (RAM);
for the selected input power P1, search through the retrieved data and determine a multitude N>1 of reflection factors Gamma included in the selected reflection factor segment and save;
and,
in a signal setting and measurements loop:
set the second VSG #2 to the P2 and Φ2 settings associated with each of the N determined reflection factors Gamma,
measure entering <a2>, departing <b2> signal power waves, and RF characteristics of the DUT;
and,
save the RF characteristics and the associated Gamma=<a2>/<b2> in a load pull file.
3. The active load pull measurement system used in the load pull measurement of claim 2 comprising:
a device under test (DUT) as part of an active load pull tuner,
and auxiliary measurement instruments,
wherein
the auxiliary measurement instruments comprise:
the two synchronized computer-controlled vector signal generators (VSG), the first VSG #1 connected to the input port #1 of the DUT, and the second VSG #2, connected to the output port #2 of the DUT,
and fixturing and DC biasing for the DUT;
and wherein
the active load pull tuner comprises:
the installed and biased DUT,
the capacity of measuring signal power waves <a> entering the DUT and <b> departing from the DUT using vector signal analyzers,
the second VSG #2,
a feedback signal power amplifier, inserted between the second VSG #2 and the output port of the DUT,
control of the vector signal generators (VSG),
calibration data.
4. The active load pull measurement system of claim 1
wherein
a driver signal amplifier is inserted between the first VSG #1 and the input port of the DUT.
5. The calibration method of claim 1 ,
wherein
the measurement capability of signal power waves <a2> entering the output port of the DUT and <b2> departing from the output port of the DUT is accomplished using a bidirectional signal coupler inserted between the output port of the DUT and the feedback signal power amplifier.
6. The measurement capability of signal power waves of claim 5 ,
wherein
the bidirectional signal coupler is connected to the vector signal analyzers.