JP2004301562A - Active load pull measuring method and active load pull measuring circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress an equivalent load reflection coefficient, namely, a frequency characteristic generated at the setting time of an equivalent load impedance, and to evaluate a wide-band load characteristic. <P>SOLUTION: This active load pull measuring method for evaluating the load characteristic of an active element such as an FET used for a high-frequency power amplifier for a radio communicator has (1) a function for flattening an amplitude frequency characteristic in an evaluation band by equalizers installed on an input signal route and a reflected wave injection route, and (2) a function for uniformizing the electric length between the routes by delay lines installed on the input signal route and the reflected wave injection route, and flattening the phase frequency characteristic in the evaluation band. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an active load-pull measuring method, and more particularly, to an active load-pull measuring method and an active load-pull measuring circuit for evaluating load characteristics of an active element such as an FET used in a high-frequency power amplifier for a wireless communication device.
[0002]
[Prior art]
A load-pull measurement method is known as a method for evaluating load characteristics of an active element such as an FET used in a high-frequency power amplifier (see Patent Document 1).
FIG. 6 is a diagram showing a basic configuration of the load-pull measurement method. This measuring method includes a signal source for outputting a signal for measurement, an active element to be measured such as a field effect transistor for inputting an output signal of the signal source, and a load impedance (Z) connected to an output terminal of the active element for measurement. _L ) is used. The load-pull measurement method evaluates load characteristics by measuring a load reflection coefficient (Γ _L ) of an active device to be measured, that is, a performance index such as output power, gain, and efficiency with respect to load impedance, using such a measurement system. This is a measurement method that enables The load characteristics obtained by the load-pull measurement method can be used as effective information for determining an output matching circuit when designing an amplifier using active elements.
[0003]
[Patent Document 1]
JP-A-56-157876 [0004]
However, in the load-pull measurement method, it is necessary to provide a variable mechanism for adjusting the load impedance in order to vary the load reflection coefficient. As this variable mechanism, a pattern adjustment for adjusting the pattern of the microstrip line, a mechanical tuner, or the like is used. However, such a variable mechanism of the load reflection coefficient requires time for setting on the adjustment mechanism, which hinders simplification and quick measurement.
[0005]
FIG. 7 is a diagram illustrating an active load pull measurement method that can solve the above-described problem. In the active load-pull measurement method, in order to solve the problem of the load-pull measurement method, a part of the input signal to the active device to be measured is branched and injected into the output of the active device to be measured as a reflected wave, which is equivalent. A load impedance (equivalent load reflection coefficient), that is, a load impedance (equivalent load reflection coefficient) can be realized.
In addition to the input signal path V1 from the signal source 1 to the active element 3 to be measured, a distributor 2 is provided at the output of the signal source 1 to branch a part of the input signal of the active element 3 to be measured. A reflected wave injection path V2 to be supplied as a reflected wave via a circulator 6 having a terminator 7 is formed on the output side of the active element 3 to be measured via the variable phase shifter 9.
[0006]
Since the equivalent load reflection coefficient is the ratio of the complex amplitude of the output wave from the active element to the injected reflected wave, the network analyzer (analyzer) is connected to the output side of the active element 3 via the coupler 4 as shown in FIG. ) 5 is provided for monitoring and measurement (calculation).
A configuration is adopted in which performance indexes such as output power, gain, and efficiency are measured for the equivalent load impedance set by the variable attenuator 8 and the variable phase shifter 9 to obtain information for evaluating load characteristics.
[0007]
With the above configuration, the variation of the equivalent load reflection coefficient in the active load-pull measurement method can be realized by adjusting the amplitude and phase of the reflected wave using the variable attenuator 8 and the variable phase shifter 9. Since it is possible to change the pattern more easily than a strip line pattern adjustment or a mechanical tuner, there is an advantage that measurement can be simplified and speeded up.
[0008]
[Problems to be solved by the invention]
However, in the conventional active load-pull measurement method, the reflected wave branched from the input signal is injected into the output of the active element and the reflection coefficient is varied, so that the frequency characteristics of the amplitude and phase of the input signal path and the reflected wave injection path are changed. Accordingly, a frequency characteristic is generated in the equivalent load reflection coefficient, that is, the equivalent load impedance, so that it is difficult to evaluate the load characteristics in a wide band. This is for the following reason.
[0009]
The signal before the branch of the reflected wave _V 0 ₌ | _V 0 | When exp (-jθ _0), the complex amplitude _{V t} after passage of the measured active element,
V _t = V ₀ · V ₁
= | V ₀ | exp (−jθ ₀ ) · | V ₁ | exp (−jθ ₁ )
= | V ₀ || V ₁ | exp (−j (θ ₀ + θ ₁ )) (Equation 1)
It becomes.
Here, V ₁ (= | V ₁ | exp (−jθ ₁ )) is an amplitude generated in an input signal path (a branch point branched as a reflected wave—an input of the active element to be measured—an output of the active element to be measured); It is based on the phase fluctuation and corresponds to the characteristics of the connection cable, the active element to be measured, and the like.
[0010]
The complex amplitude of the reflected wave injected into the active element to be measured is
_{V r} = V 0 · V ₂
= | V ₀ | exp (−jθ ₀ ) · | V ₂ | exp (−jθ ₂ )
= | V ₀ || V ₂ | exp (−j (θ ₀ + θ ₂ )) (Equation 2)
It becomes.
Here, V ₂ (= | V ₂ | exp (-jθ ₂ )) is a reflected wave injection path (a branch point branched as a reflected wave to an impedance adjusting attenuator, a phase shifter to an output of the active element to be measured). This is based on the generated amplitude and phase fluctuations, and corresponds to characteristics of a connection cable, a variable attenuator, a variable phase shifter, an isolator, and the like.
[0011]
Since the equivalent load reflection coefficient _{Ｌ L} ′ due to reflected wave injection is the ratio between V _t and V _r ,
_{Γ L '= V r / V} t
= | V ₀ || V ₁ | exp (−j (θ ₀ + θ ₁ )) / | V ₀ || V ₂ | exp (−j (θ ₀ + θ ₂ ))
= | V ₁ | / | V ₂ | exp (−j (θ ₁ −θ ₂ )) (Equation 3)
It becomes.
[0012]
Therefore, as can be seen from (Equation 3), the cause of the frequency characteristic of the equivalent load reflection coefficient Γ _L ′ (phase _{Ｌ L} ′) is:
(I) frequency characteristics of | V ₁ |
(Ii) frequency characteristics of | V ₂ |
(Iii) frequency characteristics of (θ ₁ −θ ₂ ),
It is in.
[0013]
As described above, in the conventional active load-pull measurement method, from the viewpoint of evaluation of load characteristics at a point frequency, the above (i) to (iii) are not taken into consideration, and the equivalent load reflection coefficient is determined by injection of a reflected wave. When set, there is a drawback that a frequency characteristic occurs and it is difficult to measure in a wide band.
[0014]
SUMMARY OF THE INVENTION An object of the present invention is to provide an active load-pull measurement method for evaluating load characteristics of an active element, which suppresses frequency characteristics generated when an equivalent load reflection coefficient, that is, an equivalent load impedance is set, and evaluates a wide-band load characteristic. Is to make it possible.
An object of the present invention is to provide an active load-pull measurement method for evaluating the load characteristics of an FET used in a high-frequency power amplifier for a radio communication device, and to set an equivalent load reflection coefficient, that is, a frequency characteristic generated when an equivalent load impedance is set. And to enable evaluation of load characteristics over a wide band.
[0015]
[Means for Solving the Problems]
In the active load-pull measuring method and the active load-pull measuring circuit of the present invention, in order to enable evaluation of a wide-band load characteristic,
(1) A function to flatten the amplitude frequency characteristics of the evaluation band by the equalizer installed in the input signal path and the reflected wave injection path,
{Circle around (2)} A function of aligning the electrical length between the paths and flattening the phase-frequency characteristics of the evaluation band by using the delay lines installed in the input signal path and the reflected wave injection path,
Having.
By having the above functions, the problems (i) to (iii) of the conventional active load pull measurement method and measurement circuit can be solved, the frequency characteristics of the equivalent load reflection coefficient are suppressed, and the load characteristics in a wide band are reduced. Enables the evaluation of (See Fig. 3)
[0016]
Specifically, the active load-pull measurement circuit of the present invention is an active load-pull measurement circuit that evaluates the load characteristics of an active device under test, and an input signal path for inputting a measurement signal to the input side of the active device under test. A reflected wave injection path for branching the measurement signal and injecting the reflected signal as a reflected wave on the output side of the active element to be measured, and an amplitude frequency of an evaluation band in one or both of the input signal path and the reflected wave injection path. An equalizer and a delay line for flattening characteristics and phase frequency characteristics are provided. The reflected wave injection path includes a variable attenuator and a variable phase shifter.
[0017]
Further, the active load-pull measurement circuit includes an analyzer for evaluating a load characteristic at an output of the active element to be measured, and a circulator having a terminator connected to the analyzer, and the reflected wave injection path. Is characterized in that a reflected wave is injected into the output side of the active device to be measured via the circulator.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the basic configuration of the active load-pull measuring method and the active load-pull measuring circuit of the present invention and an embodiment of the present invention will be described.
(Description of configuration)
FIG. 1 is a diagram showing a basic configuration of an active load pull measurement system according to the present invention. The input signal path (V 1) receives the signal source 1, the distributor 2 that inputs the output Vo of the signal source 1, the equalizer EQL 11, the delay line 12 that receives the output of the equalizer EQL 11, and the output of the delay line 12. The reflected wave injection path (V2) includes a variable attenuator 8 that receives a branch output from the distributor 2 and a variable phase shifter 9 that receives an output of the variable attenuator 8. , An equalizer EQL13 for receiving the output of the variable phase shifter 9, a delay line 14 for receiving the output of the equalizer EQL13, and a circulator for receiving the output of the delay line 14. It is provided on the output side, is connected via a coupler 4 connected to a network analyzer (analyzer) 5, has a terminator 7, Composed of the circulator 6 and having a directional coupling function of injecting a reflected wave to the child 3.
[0019]
The active load-pull measurement system shown in FIG. 1 has a function of flattening the amplitude frequency characteristics of the evaluation band by the equalizers 11 and 13 provided in the input signal path (V1) and the reflected wave injection path (V2). In addition, the delay lines 12 and 14 provided in the input signal path (V1) and the reflected wave injection path (V2) have the function of aligning the electrical length between the paths and flattening the phase frequency characteristics of the evaluation band. .
[0020]
(Description of operation)
The characteristics obtained by the configuration of the present embodiment will be described below by comparison with the related art. First, a measurement example using a conventional active load pull measurement system will be described.
FIG. 2 is a diagram illustrating a measurement example using a conventional active load pull measurement system. In this measurement example, since the evaluation of the load characteristics at the point frequency is considered, the amplitude frequency characteristics of the input signal path (V1), the amplitude frequency characteristics of the reflected wave injection path, and the phase difference frequency characteristics between the paths are considered. Absent. The input signal path (V1) has a physical length of 1 m, an electrical length of 3.3 ns, | V1 | = 0 dB at 1 GHz, θ1 = 1187 °, | V1 | = 1 dB at 1.1 GHz, θ1 = 1307. °. The reflected wave injection path (V2) has a physical length of 2 m, an electrical length of 6.7 ns, | V2 | = 0 dB at 1 GHz, θ2 = 2408 °, | V2 | = 0.5 dB at 1.1 GHz, θ2 = 2654 °.
[0021]
In this example, at 1 GHz and 100 MHz band,
-Amplitude frequency characteristics of input signal path: 1 dBpp (pp: peak to peak)
-Amplitude frequency characteristic of reflected wave injection path: 0.5 dBpp
-Phase difference frequency characteristic between paths: 126 ° pp
It is.
[0022]
FIG. 3 shows the frequency characteristics when the equivalent load reflection coefficient is set to the open points (| Γ _L ′ | = 1, ∠Γ _L ′ = 0 °) at 1 GHz by the conventional measurement system shown in FIG. It is a figure showing a calculation result. As shown in FIG. 3, according to the present measurement system, a frequency characteristic of 0.056 occurs in | Γ _L ′ | and a frequency characteristic of 126 ° occurs in ∠Γ _L ′, and it is difficult to evaluate a wide-band load characteristic. Can be confirmed.
[0023]
FIG. 4 is a diagram showing a measurement system of a specific embodiment of the active load pull measurement method and the active load pull measurement circuit of the present invention. Due to the equalizer and the delay line, the input signal path (V1) has a physical length of 2 m, an electrical length of 6.7 ns, | V1 | = 0 dB and θ1 = 2408 ° at 1 GHz, and | V1 | = 0 dB at 1.1 GHz. , Θ1 = 2654 °. The reflected wave injection path (V2) has a physical length of 2 m, an electrical length of 6.7 ns, | V2 | = 0 dB and θ2 = 2408 ° at 1 GHz, and | V2 | = 0 dB and θ2 = 1.1 GHz. Set to 2654 °.
[0024]
By the equalizer and the delay line installed in each path, the above setting enables the amplitude frequency characteristic of the input signal path to be 0 dBpp.
-Amplitude frequency characteristic of reflected wave injection path: 0 dBpp
-Phase difference frequency characteristic between paths: 0 ° pp
Can be improved.
[0025]
FIG. 5 is a diagram showing calculation results of frequency characteristics when an equivalent load reflection coefficient is set at an open point at 1 GHz. | Γ _L '| of the frequency characteristic is 0, ∠Γ _L' frequency characteristic of 0 ° are improved pp, it can be confirmed that it is possible to set the no equivalent load reflection coefficient frequency characteristic.
[0026]
In the embodiment described above, the configuration example in which the equalizer and the delay line are connected to both the input signal path and the reflected wave injection path has been described. However, according to the characteristics of the signal path, only one of them is connected, or the equalizer or By connecting one or both of the delay lines to one or both of them, it can be configured to improve the amplitude frequency characteristics and phase difference frequency characteristics, and can be configured to improve the accuracy of wideband load characteristic evaluation. It is.
[0027]
【The invention's effect】
According to the present invention, in an active load-pull measurement method, a method of suppressing an amplitude frequency deviation and a phase frequency deviation of a signal path causing a frequency characteristic of an equivalent load reflection coefficient by an equalizer and a delay line installed in a measurement system. Thus, the frequency characteristic of the equivalent load reflection coefficient is suppressed, and the performance index such as output power, gain, and efficiency is measured, so that it is possible to realize a wide-band load characteristic evaluation.
[Brief description of the drawings]
FIG. 1 is a diagram showing one embodiment of an active load pull measurement method of the present invention.
FIG. 2 is a diagram showing a specific example of a conventional active load pull measurement method.
FIG. 3 is a diagram showing a calculation result of an equivalent load reflection coefficient of a specific example of the conventional active load pull measurement method.
FIG. 4 is a diagram showing a specific example of a measurement method (system) according to an embodiment of the present invention.
FIG. 5 is a diagram showing a calculation result of an equivalent load reflection coefficient according to an embodiment of the present invention.
FIG. 6 is a diagram illustrating a conventional load-pull measurement method.
FIG. 7 is a diagram illustrating a conventional active load pull measurement method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Signal source 2 Distributor 3 Active element to be measured 4 Coupler 5 Network analyzer 6 Circulator 7 Terminator 8 Variable attenuator 9 Variable phase shifter 11, 13 Equalizer 12, 14 Delay line

Claims (5)

In the active load pull measurement method for evaluating the load characteristics of the active element to be measured,
An active load pull, wherein an equalizer is provided in an input signal path of the active element to be measured and an equalizer is provided in a reflected wave injection path of the active element to be measured, so that an amplitude frequency characteristic of an evaluation band is flat. Measurement method. 2. The active load-pull measurement according to claim 1, wherein delay lines are installed in the input signal path and the reflected wave injection path, electric lengths between the paths are made uniform, and a phase frequency characteristic of an evaluation band is made flat. Law. In an active load-pull measurement circuit for evaluating the load characteristics of an active element to be measured,
An input signal path for inputting a measurement signal to the input side of the active element to be measured, and a reflected wave injection path for branching the measurement signal to the output side of the active element to be measured and injecting the reflected signal as a reflected wave, An active load-pull measuring circuit, comprising: an equalizer and a delay line for flattening the amplitude frequency characteristic and the phase frequency characteristic of the evaluation band in one or both of the input signal path and the reflected wave injection path. 4. The active load pull measurement circuit according to claim 3, wherein the reflected wave injection path includes a variable attenuator and a variable phase shifter. The output of the active device to be measured includes an analyzer for evaluating a load characteristic, and a circulator having a terminator connected to the analyzer.The reflected wave injection path is connected to the active device to be measured via the circulator. 5. The active load pull measurement circuit according to claim 3, wherein a reflected wave is injected into an output side of the element.

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