Digital hybrid load pull system
View Patent ↗A digital high-speed hybrid load pull test system comprises a slide screw automatic passive tuner, a digital active forward injection loop in a closed loop transmission configuration, calibration and tuning algorithms. The forward active injection loop comprises at least one adjustable coupler, a digital electronic tuner and feedback power amplifier; the passive tuner comprises one or more metallic tuning probes, used to create passive reflection factors. Small signal calibration of the passive and active tuners create a global calibration data base, used to pre-tune in the area of the target impedance and final high power (nonlinear) tuning employs a in-situ signal power wave search and measurement for digital impedances around the small signal pattern. The system provides for high speed low injected power tuning with maximum reflection factor at DUT reference plane reaching unity.
1. A digital hybrid load pull tuner comprising:
a digital, closed loop active signal injection tuner, and
an electro-mechanical (passive) slide screw tuner, both said tuners using a common slotted airline (slabline) having a test port and an idle port and being divided into two sections, a first section towards the test port hosting part of the active injection tuner, and a second section towards the idle port hosting the passive slide screw tuner;
wherein
the digital, closed loop active signal injection tuner comprises:
a digital electronic tuner including N switching elements (N>4) and having a test port and an idle port, and
a circulator having three ports, port #1, port #2 and port #3, and two signal couplers incorporated in the slabline, a first adjustable signal coupler and a second signal coupler, each having an input, an output, a coupled and an isolated port, and a magnetic coupling loop inserted into the slabline, and an amplifier having an input and an output port;
and wherein
both signal couplers share the slabline,
the first adjustable signal coupler is mounted on a first mobile carriage towards the test port of the slabline, and the second signal coupler is inserted between the first adjustable signal coupler and the slide screw tuner;
and wherein
the coupled port of the first signal coupler is connected to the port #1 of the circulator, the port #2 of the circulator is connected to the test port of the digital electronic tuner, the port #3 of the circulator is connected to the input port of the amplifier, and the output port of the amplifier is connected to the coupled port of the second signal coupler.
2. The digital hybrid load pull tuner of claim 1
wherein
the electro-mechanical slide screw tuner is mounted in the second section of the slabline and comprises:
at least one, remotely controlled, mobile carriage sliding along the slabline and carrying at least one, remotely controlled, reflective tuning probe, insertable perpendicularly into the slot of the slabline.
3. The digital hybrid load pull tuner of claim 1
wherein
the first adjustable signal coupler comprises
a magnetic coupling loop attached to a vertically adjustable axis of the first mobile carriage and insertable into the slot of the slabline.
4. A small signal calibration method for the digital hybrid load pull tuner of claim 1 comprising the following steps:
a) calibrating the passive slide screw tuner, between the test port and the idle port of the slabline with the active tuner turned OFF,
wherein
a1) s-parameters between the test port and the idle port of the slabline are measured with the tuning probes withdrawn from the slabline, and saved as matrix [SP0]; s-parameters between the test port and the idle port of the slabline are measured for a multitude of horizontal XT and vertical YT positions of each individual tuning probe, all remaining probes having been withdrawn from the slabline, and saved as matrices [SP(XT, YT)];
a2) s-parameters of all tuning probes, except of the tuning probe closest to the test port, are de-embedded (cascaded with the inverse matrix [SP0] −1 ) and permutations of cascaded s-parameters of all tuning probes are calculated and saved;
b) calibrating the digital, closed loop active injection tuner, with the passive tuning probes withdrawn from the slabline, in two steps:
b1) calibrating the digital electronic tuner;
b2) calibrating the digital active injection closed loop;
wherein
b1) the digital electronic tuner is calibrated between its test the idle ports as follows:
b1.1) s-parameters are measured with all N>1 digital switches set to OFF (open) and saved as [SD0] matrix,
b1.2) each individual switch Di (1≤i≤N) is turned ON (closed), all other switches being set to OFF, and s-parameters are measured and saved in matrices [SDi];
b1.3) all s-parameter matrices [SDi], except for [SDI], are cascaded with the invers matrix [SD0] −1 and saved;
b1.4) all 2 N permutations of all s-parameter matrices in step b1.3) are generated in computer memory and saved as matrices [SDj] for (1≤j≤2 N );
b2) the digital, active injection closed loop is calibrated as follows:
b2.1) the reflection factor S11 is measured at the test port of the slabline, with an OPEN connected to port #2 of the circulator, for a multitude of NX horizontal (XC) positions of the first carriage and NY vertical (YC) positions of the vertical axis of the first carriage and saved as S11 (XC, YC);
b2.2) the NX*NY reflection factors S11 (XC, YC) of step b2.1) are multiplied with the reflection factors S11 of the 2 N s-parameter permutations of matrices [SDj] of step b1.4) and saved.