Active impedance tuner for base-band load pull
View Patent ↗A base-band (kHz to MHz range) very low frequency active impedance tuner allows controlling the reflection factor at a multitude of frequencies in the base-band for systematic evaluation of the effect of bias networks on nonlinear quantities of a RF transistor, like EVM and ACPR. It comprises an electronically controlled active heterodyne feedback loop, frequency mixing, filtering and a remotely controlled digital electronic tuner. The digital electronic tuning feedback module operates at standard octave band GHz range, which allows controlling impedances over several decades in the base-band frequency range.
1. An active load pull tuner, having a test port, comprises:
a base band low frequency section, and
a high frequency section, linked with the base band section using an up- and a down-conversion module, both said modules being driven by a common local oscillator, and
a digital electronic tuning module, residing in the high frequency section, and inserted between the up- and down-conversion modules;
wherein
a coupling module, comprising a power combiner/divider, links a port of a DUT with the active load pull tuner by collecting base band frequency signal from the port of the DUT, injecting it into the up-conversion module, receiving it from the down-conversion module amplified using an amplifier, and re-injecting it into the port of the DUT.
2. The active load pull tuner of claim 1 ,
wherein
the digital electronic tuning module comprises:
a circulator having ports 1, 2 and 3, and
a digital electronic impedance tuner;
and wherein
port 1 of the circulator is connected with the up-conversion module,
port 2 of the circulator is connected with the digital electronic tuner, and
port 3 of the circulator is connected with the down-conversion module.
3. The active load pull tuner of claim 1 ,
wherein
the power combiner/divider has a common port and two input/output (I/O) ports, an I/O port 1 and an I/O port 2,
and wherein
the common port is linked with the test port, which is connected with the DUT port,
the I/O port 1 is connected with the up-conversion module,
the I/O port 2 is connected with an output port of the amplifier,
and wherein
an input port of the amplifier is connected with the down-conversion module.
4. The active load pull tuner of claim 1 ,
wherein
the up-conversion module comprises a first image rejection mixer (IRM 1 ) and the down-conversion module comprises a second image rejection mixer (IRM 2 ).
5. The active load pull tuner of claim 4 ,
wherein
each image rejection mixer includes a high frequency (RF) port, a local oscillator (LO) port and an intermediate (low) frequency (IF) port,
and wherein
the IF port of the IRM 1 is connected with the I/O port 1 of the power combiner/divider,
the LO ports of the IRM 1 and the IRM 2 are connected with the local oscillator, and
the RF port of the IRM 1 is connected to port 1 of the circulator and the RF port of the IRM 2 is connected to port 3 of the circulator.
6. The active load pull tuner of claim 5 ,
wherein
a low pass filter is inserted between the IF port of the IRM 2 and the input port of the amplifier.
7. A calibration method for the active load pull tuner of claim 1 at a multitude of M≥100 states of the digital electronic tuner and a multitude N>1 of frequencies F i with 1≤i≤N, comprising the following steps:
a) connect a RF&DC port of a bias network to a first port of a slide screw tuner and terminate a RF port of the bias network with Zo;
b) connect a DC port of the bias network with the test port of the active load pull tuner;
c) connect a second port of the slide screw tuner to a pre-calibrated vector network analyzer (VNA);
d) in a control loop of j states, with j=1, 2, 3 . . . M, of the digital electronic tuner, execute nested frequency sweeps of the N frequencies F i , measure a total of M×N reflection factors Γ(j, F i ) as a function of the M states of the digital electronic tuner and the N frequencies and save in a tuner calibration file.