An active load-drag system

Abstract

The application discloses an active load pulling system, which aims at overcoming the problem of increasing oscillation and high performance requirement of a power amplifier in the prior art, and comprises a circulator, a phase shifter and a combiner which are arranged together in a head-to-tail mode, wherein the circulator, the phase shifter and the combiner form a loop structure, the circulator is used for connecting a radio frequency test system, and the combiner is connected with a first signal generator.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of radio frequency test, and particularly relates to an active load pulling system. BACKGROUND

[0002] With the continuous development of wireless communication technology, the working environment of communication devices such as base stations and smart phones is increasingly complex and diverse, and the requirements for the integrated circuits inside the radio frequency front end, i.e., the radio frequency power amplifier, are also increasing. In order to successfully complete the design of microwave / millimeter wave integrated circuits, achieve higher performance and higher integration, and at the same time reduce the number of design iterations, it is necessary to accurately test various semiconductor devices such as active and passive devices and interconnection structures in the integrated circuit, and develop accurate device models on this basis to achieve successful design of microwave / millimeter wave integrated circuits.

[0003] For radio frequency testing, impedance tuning is an important component. The purpose of impedance tuning is to obtain the optimal characteristics of the output power, gain and PAE of the device under test. It is very similar to impedance matching, which is to make the device work at the optimal characteristics through harmonic source / load matching under small signal conditions, and this setting assumes that the input / output impedance is a fixed value. However, as the input power increases, the semiconductor device enters the nonlinear region, and its input / output impedance will also change. At this time, impedance tuning of the harmonic source / load is needed to find the best impedance point of the semiconductor device. As for the impedance tuning system, it can be divided into passive and active ways.

[0004] The passive impedance tuning system adopts the combination of central conductor and tuning probe, and forms the generation of arbitrary impedance by changing the relative position between the central conductor and the ground wire to change the impedance in amplitude and phase. Because the impedance tuner used is a passive structure, it is called passive / passive impedance tuning technology. Advantages: (1) fast impedance tuning; (2) high power handling capability and large power device measurement without nonlinear effects; (3) ease of use; (4) relatively low experimental cost; (5) low maintenance cost; (6) no oscillation. However, the existing passive impedance tuning system has the following defects: the mechanical structure needs to be moved constantly, which is easy to wear and tear, and the system calibration accuracy decreases rapidly after the loss (the system can achieve a reflection coefficient of less than 0.9), making it difficult to meet the accuracy requirements for precise testing; and as the core component of impedance tuning, the waveguide itself has inherent loss that increases rapidly with frequency, which limits the application of wideband.

[0005] The active impedance tuning system can also change the device end impedance by changing the echo, and such a system by active signal injection is called an active / active arbitrary impedance test system. Advantage: in theory, any size of impedance can be synthesized. The existing active impedance tuning system can be divided into two types, namely open loop and closed loop. The open loop system needs to synthesize the required impedance through algorithm iteration. For high-power devices, since their output impedance is too small, the corresponding optimal impedance needs to be synthesized by providing higher power at the load end. For this purpose, an additional high-gain high-linearity RF power amplifier is needed for testing, which results in high testing cost. The closed loop system does not need to synthesize the required impedance through algorithm iteration, but since there is a loop in the RF test system, it increases the risk of oscillation and cannot avoid the impedance iteration requirement of the RF high-power amplifier. Therefore, the above two types of impedance tuning systems have their own shortcomings. SUMMARY

[0006] In order to overcome the shortcomings and problems of the prior art, the present application provides an active load pulling system.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] An active load pulling system comprises a circulator, a phase shifter and a combiner which are arranged together in a ring, the circulator, the phase shifter and the combiner form a loop structure, the circulator is connected to an RF test system, and the combiner is connected to a first signal generator.

[0009] Preferably, the circulator comprises a first port, a second port and a third port, the RF test system is connected to the first port, the second port is connected to the phase shifter, and the third port is connected to the combiner.

[0010] Preferably, the combiner comprises a first input end, a second input end and a combiner transmitting end, the first input end is connected to the phase shifter, the second input end is connected to the first signal generator, and the combiner transmitting end is connected to the circulator.

[0011] Preferably, the phase of the phase shifter is adjustable.

[0012] Preferably, the RF test system comprises a vector network analyzer, and the vector network analyzer is used to receive the input signal and the reflected signal of the device under test.

[0013] Preferably, the vector network analyzer comprises an input test port and a reflection test port, the input test port is used to receive the input signal of the device under test, and the reflection test port is used to receive the reflected signal of the device under test.

[0014] As preferred, the radio frequency test system comprises a first coupler and a second coupler, the input test port is connected to the first coupler, and the reflection test port is connected to the reflection test port.

[0015] As preferred, the radio frequency test system further comprises a second signal generator.

[0016] As preferred, the radio frequency test system further comprises a radio frequency power amplifier, which is connected to the second signal generator.

[0017] As preferred, the radio frequency test system comprises a first biasing device and a second biasing device, and the vector network analyzer is connected between the first biasing device and the second biasing device.

[0018] The present application has the following prominent and beneficial technical effects compared with the prior art:

[0019] Compared with the traditional active open-loop impedance tuning system, the present application forms a semi-open-loop active impedance tuning structure, and the power amplifier can synthesize a larger transmission coefficient under smaller radio frequency power, effectively reducing the performance requirements of the radio frequency power amplifier in terms of gain and linearity.

[0020] Compared with the traditional active closed-loop impedance tuning system, the radio frequency test system of the present application does not need the radio frequency power amplifier to iterate the impedance, greatly reducing the risk of oscillation.

[0021] In actual measurement, it is found that under the premise of limiting the maximum power of the output signal of the radio frequency test system, the phase shifter is used to continuously change the phase of the signal, so that a larger tunable load impedance range can be obtained, and therefore the active load traction system is effectively improved in high reflection impedance tuning capability. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is one of the system framework structure schematic diagrams of the present application;

[0023] Figure 2 is the second system framework schematic diagram of the present application;

[0024] Figure 3 is the framework structure schematic diagram of the traditional open source load traction system;

[0025] Figure 4 is the Smith chart obtained by theoretical analysis of the present application and the traditional open source load traction system;

[0026] Figure 5 is the actual schematic diagram of the test platform built according to the present application;

[0027] Figure 6 is the actual schematic diagram of the phase shifter in the test platform;

[0028] Figure 7 is a physical schematic diagram of a circulator in a test platform;

[0029] Figure 8 is a physical schematic diagram of a combiner in a test platform;

[0030] Figure 9 is a Smith chart obtained by a test platform built according to the present application and a traditional open-source load-drag system;

[0031] In the figure: 1-circulator, 2-phase shifter, 3-combiner, 4-rf test system, 5-first signal generator. DETAILED DESCRIPTION

[0032] In order to facilitate the understanding of those skilled in the art, the present application is further described below in conjunction with the drawings and specific embodiments.

[0033] As shown in Figures 1 to 9 , an active load-drag system includes an rf test system, a circulator, a phase shifter, a combiner, and a first signal generator. The circulator, phase shifter, and combiner are arranged in a loop structure. The first signal generator is connected to the combiner, and the rf test system is connected to the circulator.

[0034] The first signal generator is used to output signals externally. The first signal generator is connected to the combiner, and in actual use, the signals output by the first signal generator are injected into the loop structure through the combiner.

[0035] The circulator is a unidirectional signal transmission multi-port device. The circulator includes a first port, a second port, and a third port. The signal on the first port can be transmitted to the second port, the signal on the second port can be transmitted to the third port, and the signal on the third port can be transmitted to the first port. However, signals cannot be injected from the second port to the first port, from the third port to the second port, or from the first port to the third port, and the circulator achieves isolation of reverse direction signal transmission. The rf test system is connected to the first port, and the signal output by the rf test system can be injected into the first port. The second port is connected to the phase shifter, and the signal output by the second port can be injected into the phase shifter. The third port is connected to the combiner, and the signal output by the combiner can be injected into the third port.

[0036] The circulator is a narrow-band circulator. In actual use, the narrow-band circulator can separate the fundamental wave and the harmonic wave in order to facilitate the test of the rf test system and improve the test performance of the rf test system. In this embodiment, the circulator is a D3C4080 model from DITOM.

[0037] The phase shifter is used to change the phase of the signal outputted from the second port of the circulator. The phase shifter is used to adjust the phase of the signal, and the phase shift adjustment range of the phase shifter to the signal is 0-360°. In actual use, the signal outputted from the radio frequency test system is injected into the phase shifter through the circulator, and by adjusting the phase shift of the phase shifter, the phase of the signal outputted from the radio frequency test system can be changed, so that the active load traction system can obtain a larger impedance tuning range. In this embodiment, the phase shifter is selected from the brand RF-LAMBDA phase shifter.

[0038] The combiner is used to combine several different frequency band signals inputted together and outputted. The combiner is a two-in-one-out device, including a first input end, a second input end and a combiner transmitting end. In actual use, the signal on the first input end and the signal on the second input end are combined and then transmitted outward by the combiner transmitting end. The first input end is connected to the phase shifter, and the signal outputted from the phase shifter can be injected into the first input end. The second input end is connected to the first signal generator, and the signal outputted from the first signal generator can be injected into the second input end. The combiner transmitting end is connected to the third port of the circulator, and the signal outputted from the combiner transmitting end can be injected into the third port of the circulator. In this embodiment, the model of the combiner is PD1040, and the brand is Marki microwave.

[0039] The radio frequency test system includes a second signal generator, a radio frequency power amplifier, a first biasing device, a first coupler, a device to be tested, a second coupler, a second biasing device and a vector network analyzer. The second signal generator, the radio frequency power amplifier, the first biasing device, the first coupler, the device to be tested, the second coupler, the second biasing device and the first port of the circulator are connected in sequence. The vector network analyzer is connected to the device to be tested. In this embodiment, the device to be tested can be a radio frequency semiconductor device.

[0040] The second signal generator is used to output signals outward. In actual use, the signal outputted from the second signal generator is injected into the first biasing device.

[0041] The radio frequency power amplifier is used to amplify the signal. The radio frequency power amplifier is connected to the second signal generator, and in actual use, the signal outputted from the second signal generator is injected into the radio frequency power amplifier, and the radio frequency power amplifier amplifies the signal.

[0042] The first bias converter is used to inject DC voltage into the RF test system. It connects between the power amplifier and the device under test (DUT) and is also connected to a DC power supply. The first bias converter is a three-port network device with three ports: an RF port, a DC bias port, and an RF DC port, arranged in a "T" shape. The DC bias port of the first bias converter is connected to the DC power supply to prevent signal leakage from the RF port. The RF port receives the signal injected by the RF power amplifier and blocks the DC voltage on the DC bias port. The RF DC port of the first bias converter is connected to the DUT via a first coupler, allowing measurement of the DC bias voltage and the signal output by the RF power amplifier. The second bias converter serves the same purpose and has the same structure as the first bias converter. Its DC bias port is connected to the DC power supply to receive the DC voltage. Its RF port is connected to the DUT to receive the signal emitted by the DUT. The RF DC port of the second bias converter is connected to the first port of the circulator.

[0043] A vector network analyzer is used to extract the input and reflected signals of a device under test (DUT). The vector network analyzer includes an input test port and a reflection test port; the input test port is connected to a first coupler, and the reflection test port is connected to a second coupler.

[0044] From a theoretical perspective, such as Figure 1 As shown, the signal transmitted from the RF test system to the circulator is b1, the signal transmitted from the circulator to the RF test system is a1, the signal transmitted from the circulator to the phase shifter is b2, the signal injected into the combiner by the phase shifter is b3, and the signal injected into the combiner by the first signal generator is a. g The signal transmitted from the combiner to the circulator is b3. If b1 is set to a constant, then the larger the signal a1 fed back by the circulator, the higher the reflection coefficient Γ of the device under test. L The larger the value, the stronger the performance characteristic of the device under test. The reflection coefficient Γ of the device under test... L It can be calculated using the following formula (1):

[0045]

[0046] The loop structure in this embodiment is low-loss, and the power P corresponding to a1 is... Lp for:

[0047]

[0048] In the formula, b2e jθ θ is the signal obtained after phase shifting b2 by the phase shifter, and θ is the phase shift angle of b2 by the phase shifter.

[0049] Equation (2) can be converted to equation (3) as follows:

[0050]

[0051] When the phase of a g and the phase of b2e jθ are the same, equation (3) is converted to equation (4) as follows:

[0052]

[0053] P max is the maximum value of P Lp .

[0054] a g corresponding to the maximum power P ref is:

[0055]

[0056] Since b2>a g , the test performance of the active load traction system is better than that of the traditional active load test system in the case of low-loss loop structure. The active load traction system combines the active open-loop method and the closed-loop impedance tuning method, which effectively reduces the demand for high-gain and high-linearity power amplifiers while ensuring the impedance of high-reflection coefficient. In order to verify the advantages of the active load traction system compared with the traditional open-loop impedance tuning system, a simulation comparison experiment was conducted on the electromagnetic field simulation software ADS, and the Smith chart as shown in Figure 4 was obtained. In the figure, "+" represents the impedance tuning range of the active load traction system in ADS simulation, and "o" represents the impedance tuning range of the traditional open-loop impedance tuning system in ADS simulation. Through the simulation comparison experiment, it can be known that the active load traction system effectively improves the high-reflection impedance tuning ability compared with the traditional open-loop impedance tuning system under the same setting conditions.

[0057] In order to verify the accuracy of the theoretical analysis, as shown in Figure 5 , a test platform of the active load traction system was built, and the phase shifter, circulator and combiner used in the loop structure are as shown in Figure 6 , Figure 7 and Figure 8The signal outputted from the second port of the circulator passes through the phase shifter and is changed in phase, and then is superimposed with the signal provided by the combiner and the first signal generator and returned to the RF test system, thereby changing the load impedance of the device under test. In order to obtain the superiority of the active load-pulling system over the conventional open-loop impedance tuning system, in the actual measurement, the maximum power of the signal outputted from the RF test system to the circulator is limited to 5dbm, and the phase shifter is used to change the phase of the signal (the phase is adjusted between 0-360°) and thereby change the position of the load impedance of the device under test on the Smith chart. The final test result is shown in Fig. 4. Figure 9 As shown in Fig. 4, each solid circle corresponds to a different phase of the phase shifter, and the dashed circle represents the range of the load impedance that can be reached by the conventional open-loop impedance tuning system. It can be found that, under the premise of limiting the power of the output signal of the RF test system, the active load-pulling system has a larger range of tunable load impedance.

[0058] In addition, in order to suppress the harmonics of the RF power amplifier and make it fully reflected, the load impedance of the active load-pulling system is usually set at the outermost circle of the Smith chart. Therefore, compared with the conventional open-loop load-pulling system which usually needs a signal source to provide a larger output power to synthesize the required impedance and has the possibility of causing the device under test to be burned out, the active load-pulling system only needs a small power to synthesize the target impedance by adjusting the phase of the signal with the phase shifter, thereby reducing the requirement for high linearity of the RF power amplifier.

[0059] The above embodiments are only the preferred embodiments of the present application, and do not limit the protection scope of the present application, so that: any equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. An active load-dragging system, characterized by The circulator, the phase shifter and the combiner are arranged together in series, the circulator, the phase shifter and the combiner form a loop structure, the circulator is connected with a radio frequency test system, and the combiner is connected with a first signal generator; the combiner comprises a first input end, a second input end and a combiner transmitting end, the first input end is connected with the phase shifter, the second input end is connected with the first signal generator, and the combiner transmitting end is connected with the circulator; the first signal generator is used for outputting a signal, and the signal output by the first signal generator is injected into the loop structure through the combiner.

2. An active load draw system according to claim 1, wherein, The circulator comprises a first port, a second port and a third port, the first port is connected with the radio frequency test system, the second port is connected with the phase shifter, and the third port is connected with the combiner.

3. An active load draw system according to claim 1, wherein, The phase of the phase shifter is adjustable.

4. An active load draw system according to claim 1, wherein, The radio frequency test system is further connected with the circulator, and the radio frequency test system comprises a vector network analyzer, and the vector network analyzer is used for receiving an input signal and a reflected signal of a device under test.

5. An active load draw system according to claim 4, wherein, The vector network analyzer comprises an input test port and a reflection test port, the input test port is used for receiving the input signal of the device under test, and the reflection test port is used for receiving the reflected signal of the device under test.

6. An active load drawing system according to claim 5, wherein, The radio frequency test system comprises a first coupler and a second coupler, the input test port is connected with the first coupler, and the reflection test port is connected with the second coupler.

7. An active load draw system according to claim 4, wherein, The radio frequency test system further comprises a second signal generator.

8. An active load draw system according to claim 7, wherein, The radio frequency test system further comprises a radio frequency power amplifier, and the radio frequency power amplifier is connected with the second signal generator.

9. An active load drawing system according to any one of claims 4 to 8, wherein, The radio frequency test system comprises a first biasing device and a second biasing device, and the vector network analyzer is connected between the first biasing device and the second biasing device.

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