CN203119882U - Path balancing in radio frequency distributor - Google Patents

Abstract

The utility model discloses path balancing in a radio frequency distributor. The distributor used for radio frequency (RF) signals comprises a plurality of electrical paths, a plurality of amplifiers and a plurality of attenuators, wherein the electrical paths are configured to send the RF signals to a plurality of output ports from an input port; the amplifiers are arranged in the corresponding electrical paths and configured to send signals in a first direction from the input port to the plurality of the output ports and to provide reverse isolation in a second direction opposite to the first direction; and the attenuators are arranged in the corresponding electrical paths and configured to attenuate a variable quantity for signals of each of the electrical paths.

Description

Path balance in the radio frequency assignment device

Technical field

The utility model relates to the path balance (path balancing) in the radio frequency assignment device (radio frequency distributor).

Background technology

Radio frequency (RF) distributor sends to a plurality of output ports with the RF signal simultaneously from an input port.The RF distributor for example can be used in the device test system RF test signal is sent to a plurality of equipment under tests (DUT) from testing apparatus.

The RF distributor of common type is Wilkinson (Wilkinson) distributor, and it uses passive multiport splitter (splitter) to distribute RF.The Wilkinson distributor receives the RF signal usually and uses the splitter that is formed by passive block the RF signal to be divided into a plurality of power paths that lead to different output ports at the input port place.Splitter can realize the RF signal being divided into the power path of arbitrary number in multistage mode.For example, No. 8 splitters can comprise: include the first order of single two-way splitter, this single two-way splitter will be divided into two power paths from the RF signal of input port; The second level that comprises two two-way splitters, these two two-way splitters are divided into four power paths with two power paths of the first order; And the third level that comprises four two-way splitters, these four two-way splitters are divided into partial four power paths eight power paths that lead to eight output ports.

The performance of RF distributor depends on two parameters that are called port amplitude balance (port amplitudebalance) and port isolation (port isolation) at least in part.The port amplitude balance refers to that the RF distributor sends to input rf signal with identical amplitude or probability the tendentiousness of its each output port.Simultaneously, port isolation refers to that the RF distributor prevents that the signal of an output port from disturbing the ability of the signal of another output port.For example, if signal is reflected at an output port, then such interference may take place, thereby causes the distortion at another output port place.

Can disturb two obstacles of port amplitude balance and port isolation to comprise non-perfect path termination (termination) and intrinsic path difference.Non-perfect path termination refers to the faulty impedance matching of element that termination is led to the power path of output port.Such element for example can comprise load, fixture (fixture) or the cable of the non-perfect coupling at each output port place.In typical case, output port may require 50 ohm load, but the practical impedance of its load may have variation slightly, thereby causes signal reflex and other undesirable behavior.

Simultaneously, intrinsic path difference refers to lead to the difference of electrical characteristics of the power path of different output ports.These differences for example can result from fabrication tolerance, such as the little standard deviation of the passive resistance in the different power paths.These differences can cause different quantity of power to be provided for each output port.

The frequency of RF distributor or associated component or amplitude dependence may further make the problem of non-perfect path termination and intrinsic path difference complicated.For example, the power path in the RF distributor depends on that the frequency of RF signal or amplitude may have different path termination characteristics, so they may experience imperfect path termination in various degree under different circumstances.Similarly, the passive block in the power path may have frequency or amplitude dependency characteristic, thereby causes the different intrinsic path difference under different circumstances.

Legacy system or assembly fully do not overcome the above problems.Therefore, need to obtain that better path amplitude balance and path isolate through improved RF distributor.

Summary of the invention

In a representative embodiment, a kind of distributor for the RF signal comprises: a plurality of power paths are configured to the RF signal is sent to a plurality of output ports from input port; A plurality of amplifiers, being disposed in the corresponding power path and being configured to send signal at the first direction from input port to a plurality of output ports provides reverse isolation in the second direction opposite with first direction simultaneously; A plurality of attenuators are disposed in the corresponding power path and are configured to the amount that the signal attenuation in each power path is variable; And controller, be configured to change attenuation in response to triggering input.

In another representative embodiment, a kind of method of the Rf of operation distributor comprises: the signal in the RF scope is sent to a plurality of output ports from input port by corresponding power path; Utilize corresponding amplifier to amplify this signal in each power path, each amplifier is configured to send this signal at the first direction from input port to a plurality of output ports, provides reverse isolation in the second direction opposite with first direction simultaneously; And utilizing decay this signal in each power path of corresponding attenuator, each attenuator is configured to provide the variable attenuation amount to this signal, and controller, is configured to change attenuation in response to triggering input.

Description of drawings

To from following detailed description, understand described embodiment best when read in conjunction with the accompanying drawings.Under suitable and practicable situation, similar label refers to similar element.

Fig. 1 is the diagram according to the device test system of a representative embodiment.

Fig. 2 is the diagram according to the RF distributor of a representative embodiment.

Fig. 3 A and Fig. 3 B are the diagrams according to No. 8 splitters that are used for the RF distributor of a representative embodiment.

Fig. 4 is the diagram according to the RF distributor of another representative embodiment.

Fig. 5 is the diagram according to the RF distributor of another representative embodiment.

Fig. 6 is the diagram according to No. 8 splitters that are used for the RF distributor of a representative embodiment.

Fig. 7 is the diagram according to the RF distributor with transmit path and RX path of a representative embodiment.

Fig. 8 is the diagram of signal route assembly of RF distributor that is used for having transmit path and RX path according to a representative embodiment.

Fig. 9 is the diagram according to the device test system of a representative embodiment.

Figure 10 is the flow chart according to the method that is used for operation RF distributor of a representative embodiment.

Embodiment

In the following detailed description, for explanation and non-limiting purpose, set forth the representative embodiment for open detail, in order to the thorough understanding to this instruction is provided.Yet, benefit from those skilled in the art of the present disclosure with clear, deviate from detail disclosed herein according to other embodiment of this instruction still within the scope of the claims.In addition, may omit the description of well known device and method, so that not fuzzy description to example embodiment.These method and apparatus drop in the scope of this instruction significantly.

Term used herein is only for the purpose of describing specific embodiment, and not to be intended to be restrictive.Defined term not only have such as in the technical field of this instruction often institute understand and accept the scientific and technical implication of definition term.As using in specification and claim, term " ", " one " and " described " comprise single reference object and a plurality of reference object, unless context otherwise clearly indicates.Therefore, for example, " equipment " comprises an equipment and a plurality of equipment.

As using in specification and claim, and except its general implication, term " basic " or " basically " mean within acceptable restriction or degree.

Described embodiment is broadly directed to RF distributor and related operating method.In certain embodiments, the RF distributor comprises a plurality of power paths that are configured to send to a plurality of output ports from input port the RF signal.A plurality of amplifiers are disposed in the respective electrical path and are configured to and send the RF signal at the first direction from input port to a plurality of output ports, provide reverse isolation in the second direction opposite with first direction simultaneously.In addition, a plurality of attenuators are disposed in the respective electrical path and the RF signal that is configured in each power path provides variable attenuation.

The reverse isolation that is provided by amplifier can prevent that the load variations at output port place is counted as the load variations of amplifier upstream.In addition, the variable attenuation that is provided by attenuator can reduce the amplitude of each bar power path and the difference of frequency response, and for example, these differences may be owing to the inherent difference between port, cable, fixture, the resistance element etc. produces.Therefore, even reverse isolation exists various forms of non-perfect path terminations and intrinsic path difference different time that port amplitude balance and port isolation through improving also can be provided in conjunction with the use of variable attenuation.

In certain embodiments, variable attenuation is to provide according to the predefined paths measurement that each power path is carried out.These predefined paths for example measure can by regulate each attenuator with high relatively resolution increment (for example, 1/4 decibel or littler) and under varying level the electrical characteristics in measuring circuit footpath carry out.In addition, also can catch these at different frequency and measure, so that attenuator can be conditioned in the mode that depends on frequency.Therefore, such predefined paths is measured the amplitude loss of depending on frequency that can indicate every power path.Predefined paths is measured and can be stored in the path loss table and accessed in the operating period of RF distributor.Other path loss table also can be generated and be used to remove the changes in amplitude that depends on frequency or the static margin that are produced by concrete cable, fixture or further feature to be changed.

These and other embodiment compares with traditional RF distributor can provide some advantages.For example, they can eliminate the changes in amplitude between the output port, and these changes in amplitude are all in this way because imperfect port load and depend on that the decay of frequency causes.In addition, they can compensate External cable and fixture loss with dynamical fashion.These and other advantage for example can be brought more accurate or more reliable measurement in test and measuring system.

Fig. 1 is the diagram according to the device test system of representative embodiment.This system represents can use according to representative embodiment a kind of example situation of RF distributor.

With reference to figure 1, device test system 100 comprises testing apparatus 105 and RF distributor 110.Testing apparatus 105 for example can comprise and is configured to encourage network analyzer or the RF signal source of one or more DUT to measure its electrical characteristics.Testing apparatus 105 comprises a plurality of I/O (I/O) port one 15, display 120 and the control panel 125 that is configured to external device communication.One of I/O port one 15 is connected to RF distributor 110 test signal is sent to one or more DUT.

RF distributor 110 comprises input port 130 and a plurality of output port 135.Input port 130 is connected to testing apparatus 105 with the acceptance test signal.RF distributor 105 receives input signal and input signal is distributed to each output port 135 by input port 130.Output port 135 can be connected to a plurality of DUT that test by testing apparatus 105.These DUT for example can be cell phones.Use with a plurality of output ports of test signal allows a plurality of DUT simulated and measurement concurrently, and this can greatly improve the efficient of test operation.Under typical circumstances, the calibration of DUT receiver may be operation the most consuming time in the test operation, therefore for example compares with use a plurality of receivers in tester, and these parallel work-flows can produce higher throughput income.

Although not shown in Figure 1, RF distributor 110 can also comprise the output port that is configured to output signal is transferred to testing apparatus 105.Such output signal for example can be the response to input signal from DUT.This additional output ports can be connected to output port 135 so that two-way (that is full duplex) communication to be provided between testing apparatus 105 and DUT.

Fig. 2 is the diagram according to the RF distributor of a representative embodiment.

With reference to figure 2, RF distributor 200 comprises input port 205, No. 8 splitters 215 and a plurality of output port 230.Input port 205 receives input signal from all testing apparatuss as shown in Figure 1, and it sends to No. 8 splitters 215 with input signal.No. 8 splitters 215 are assigned to input signal in 8 power paths that lead to corresponding output port 230.

Indicated as the four-headed arrow among Fig. 2, RF distributor 200 can also comprise for the assembly that two-way communication is provided between testing apparatus and DUT.This two-way communication can provide by for example using directional coupler to replenish reverse communication path to No. 8 splitters 215, as described about each following example.Can also carry out directional couple at input 205 places, although between this implementation and other implementation, there is compromise usually.

Fig. 3 A and Fig. 3 B are the diagrams according to No. 8 splitters that are used for the RF distributor of a representative embodiment.This No. 8 splitter for example can be used as the core of No. 8 splitters 215 as shown in Figure 2.

With reference to figure 3A, No. 8 splitters 300 comprise the first order 305, the second level 310 and the third level 315 of cascade arrangement.The first order 305 comprises single broadband splitter (for example, resistive 6dB splitter), and this broadband splitter has the directed amplifier that is positioned at its each output place.Generally, because directed Amplifier Gain, these assemblies have formed active splitter.Similarly, the second level 310 is included in two resistive splitters that its output place has directed amplifier, and the third level 315 is included in four resistive splitters that its each output place has directed amplifier.

The RF input signal is provided for the input of the first order 305, and active splitter, the second level and the third level of this input signal process first order 305, and to produce 8 RF output signals, these 8 RF output signals are isolated from each other well owing to directed amplifier.Although Fig. 3 has illustrated resistive splitter in every grade, these can be replaced by the splitter of other type.In addition, among No. 8 splitters 300 of Fig. 3 A or each embodiment that its variant can be used to be described below the RF signal is separated.For example, Fig. 3 B shows a variant that only comprises No. 8 splitters 300 of directed amplifier at the third level 315 places.In the example of Fig. 3 B, the resistive splitter shown in Fig. 3 A is replaced by the Wilkinson splitter.

Fig. 4 is the diagram according to the RF splitter of another representative embodiment.Except Fig. 4 showed the decay of the power path corresponding with output port 230, Fig. 4 and Fig. 2 were similar.

With reference to figure 4, the same with the example of Fig. 2, RF distributor 400 comprises input port 205, No. 8 splitters 215 and a plurality of output port 230.RF distributor 400 also comprises a plurality of static decay devices 405 of each power path corresponding with output port 230 that be configured to decay.From output port 230 as seen, static decay device 405 has reduced to be present in the influence that the load matched at output port 230 places changes.

Fig. 5 is the diagram according to the RF distributor of another representative embodiment.Except the RF distributor of Fig. 5 comprised the variable attenuator that is arranged in the power path corresponding with output port 230, Fig. 5 and Fig. 4 were similar.

With reference to figure 5, the same with the example of Fig. 2, RF distributor 500 comprises input port 205, No. 8 splitters 215 and output port 230.RF distributor 500 also comprises a plurality of static decay devices 510 and a plurality of variable attenuator 505 that is arranged in the corresponding power path of output port 230, and the controller 515 that is configured to control the attenuation that each variable attenuator 505 provides.

Controller 515 control variable attenuators 505 are to apply variable attenuation to each power path.This variable attenuation generally is used to provide the port amplitude balance to output port 230.Although variable attenuator 505 is shown to have-default value of 3dB, and they can also get various substitution value to depend on situation.In addition, in certain embodiments, variable attenuator 505 can be conditioned to obtain high-caliber port balance with fine-resolution (for example, 1/4dB or littler increment).

In certain embodiments, the adjusting of being undertaken by controller 515 is determined according to the predetermined value of determining by calibration process.For example, calibration process can be in the electrical characteristics directly of measuring circuit under the different condition to determine required adjusting.These adjustings can be stored in the table (for example, path loss table) then as one group of predetermined value.In certain embodiments, these values are determined by following operation: apply calibrating signal and with little increment (for example to input port 205 under different frequency, 1/4) regulates each variable attenuator 505, depend on the behavior of frequency and determine that they are to the influence of the overall port amplitude balance of RF distributor 500 to determine them.

Controller 515 comprises the known treatment equipment that uses software, firmware, hard-wired logic or its combination, for example processor or CPU (CPU), application-specific integrated circuit (ASIC) (ASIC), field programmable gate array (FPGA) or its combination.When using processor or CPU, but the memory (not shown) is included executive software/firmware and/or the executable code that makes it possible to carry out various functions for storage.Memory can be non-volatile read-only memory (ROM) and the volatile random access memory (RAM) of arbitrary number, type and combination, and can store various types of information, such as computer program and the software algorithm that can be carried out by processor or CPU.Memory can comprise the tangible computer-readable recording medium of arbitrary number, type and combination, for example disk drive, EPROM (EPROM), Electrically Erasable Read Only Memory (EEPROM), CD, DVD, USB (USB) driver etc.

Memory can comprise the tangible computer-readable recording medium of arbitrary number, type and combination, for example disk drive, EPROM (EPROM), Electrically Erasable Read Only Memory (EEPROM), CD, DVD, USB (USB) driver etc.

As mentioned above, controller comprises FPGA.FPGA for example can comprise the state machine that different trigger events are responded, and different trigger events for example are to apply different frequency or from user's expression order or certain automation mechanism to input port 205.In response to trigger event or order, state machine can dynamically change the hardware configuration of RF distributor 500, for example, and to apply different path correcting attenuations to variable attenuator 505.

Fig. 6 is the diagram according to the RF distributor of another representative embodiment.Provide the active buffering except the embodiment of Fig. 6 is provided as variable attenuator 505, the embodiment of Fig. 6 is similar to Fig. 5.

With reference to figure 6, the same with the example of Fig. 5, RF distributor 600 comprises input port 205, No. 8 splitters 215, output port 230, static decay device 510 and variable attenuator 505.In addition, RF distributor 600 also comprises a plurality of directed amplifier 605 that is arranged in the power path corresponding with output port 230.Directed amplifier 605 provides port isolation for variable attenuator 505 provides active buffering and them can also be utilized for output port 230.This port isolation can reduce the influence of load change, signal reflex and other electrical activity at output port 230 places.This also can tackle the change in electrical characteristics that may be produced by different fixing device, cable or other assembly at output port 230 places.Directed amplifier 605 is positioned at the upstream of variable attenuator 505, to determine the constant load on No. 8 splitters 215.The other directed amplifier 610 that is positioned at variable attenuator 505 downstreams provides stable load impedance to output port 230.The variable attenuator of real world arranges in difference usually has different couplings down, therefore utilizes amplifier to cushion them and will help output impedance to keep constant.

Fig. 7 is the diagram according to the RF distributor with transmission and RX path of a representative embodiment.

With reference to figure 7, RF distributor 700 comprises transmit path, and this transmit path comprises the feature identical with RF distributor 600 between input port 205 and output port 230.RF distributor 700 also comprises RX path, and RX path comprises a plurality of transmission line directional couplers 705, switch tree 710 and output port 715.Alternatively, switch tree 710 for example can be replaced by single 8 way switch.

Transmission line directional coupler 705 is disposed between output port 230 and the switch tree 710 to allow that the RF signal is sent to testing apparatus from a plurality of DUT.Switch tree 710 comprises a plurality of switches that can be used to signal is sent to from arbitrary output port 230 output port 715.In other words, switch tree 710 is used as the port selection tree for the RX path of RF distributor 700.

During the typical operation of RF distributor 700, input port 205 is from as shown in Figure 1 testing apparatus acceptance test signal.Test signal is sent to output port 230 by the feature of the RF distributor 600 represented by the black surround among Fig. 7.Test signal is applied to DUT via output port 230, and DUT produces response signal based on test signal.Response signal is sent to output port 715 via transmission line directional coupler 705 and switch tree 710 from output port 230 then.

Fig. 8 is the diagram according to the signal route assembly of the RF distributor with transmission and RX path of a representative embodiment.This signal route assembly can be used to the two-way communication between auxiliary test unit and the DUT.Similarly, a plurality of signal route assemblies can be used to the two-way communication between auxiliary test unit and a plurality of DUT.

With reference to figure 8, the transmit path that signal route assembly 800 comprises between transmit port Tx and the DUT, and the RX path between receiving port Rx and the DUT.Transmit path is from testing apparatus acceptance test signal and at transmitted test signal on the first direction of DUT.Simultaneously, RX path receives response signal and is transmitting response signal towards the second direction of testing apparatus from DUT.Signal route assembly 800 comprises directional coupler, and it allows to communicate by letter with DUT simultaneously basically on both in first and second directions.

Transmit path comprises variable attenuator 805, directed amplifier 810, directional coupler 815 and calibration switch 820.Variable attenuator 805 variable adjustment are providing the port amplitude balance in the RF distributor, and directed amplifier 810 can be used to provide reverse isolation in transmit path.In addition, variable attenuator 805 noise that can be used to decay and for example in the active splitter chain shown in Fig. 3 A and Fig. 3 B, generate.Directional coupler 815 allows to communicate simultaneously basically in transmit path and RX path.

During the calibration process at transmit path, calibration switch 820 is routed to detector diode 840 with input signal from transmit port Tx.The characteristic of transmit path when variable attenuator 805 is adjusted to various levels with definite different frequency and differential declines level.Input signal when detector diode 840 is measured decay and frequency translation.Detector diode 840 is usually located near certain point of the output of RF distributor and sentences just the characteristic of determining the output signal that will be seen by DUT exactly.

RX path comprises calibration switch 820, directional coupler 815 and switch 845.During typical operation, the output signal of DUT is sent out via directional coupler 815 passes through RX path.As indicated above, can with send input signal by transmit path and side by side transmit these signals.During the calibration process at RX path, calibration switch 820 is routed to switch 845 with signal from DUT.

Attenuator in the signal route assembly 800 and on off state can be controlled by the state machine in the FPGA.This allows to come state changed via single triggering input to control separately.In addition, in the system that comprises a plurality of signal route assemblies, in all systems as shown in Figure 9, it can be used to the state in a plurality of signal route assemblies is changed the control carry out basically simultaneously.In addition, in these embodiments, port amplitude balance (or attenuator balance) algorithm can use the path loss data that had before recorded to consider any imperfect attenuation step of variable attenuator.

Fig. 9 is the diagram according to the device test system of a representative embodiment.How the various features that this embodiment illustrates such as the signal route assembly of Fig. 8 can test with actuating equipment with further feature is combined.

With reference to figure 9, device test system 900 comprises testing apparatus 105, No. 8 splitters 300, a plurality of signal route assembly 905 and switch tree 910.Each signal route assembly 905 can be implemented similarly with the signal route assembly 800 of Fig. 8.Therefore, these assemblies can allow to carry out the two-way communication of while basically between testing apparatus 105 and a plurality of DUT.Switch tree 910 allows to select one of eight ports, and comprises in addition outer field switch allowing the signal transmission by buffer or the amplifier except switch tree 910, and the switch tree 710 of itself and Fig. 7 is similar.This amplifier is used as the prime amplifier from the low level signal of DUT.It was placed in the chain before other loss rising thermal noise floor earlier.

Figure 10 is the flow chart according to the method that is used for operation RF distributor of a representative embodiment.This method for example can be performed in such as Fig. 1 or device test system shown in Figure 9.In the following description, the exemplary method step is indicated by bracket (SXXX).

With reference to Figure 10, method 1000 comprises the RF signal is sent to a plurality of output ports (S1005) from the power path of input port by correspondence.For example, in the embodiment of Fig. 9, input signal can be sent to eight output ports that are connected to eight corresponding DUT from the single input port that is connected to testing apparatus 105.

This method also comprises utilizes corresponding amplifier to amplify RF signal in each power path, each amplifier is configured to send the RF signal at the first direction from input port to a plurality of output ports, provides reverse isolation (S1010) in the second direction opposite with first direction simultaneously.An example of such amplifier is directed amplifier 810 shown in Figure 8.This method also comprises utilizes decay RF signal in each power path of corresponding attenuator, and each attenuator is configured to provide variable attenuation amount (S1015) to the RF signal.The variable attenuator 805 that an example of such attenuator is Fig. 8.These attenuators can provide variable attenuator based on the predetermined value of determining by calibration process.By reverse isolation and variable attenuation are provided in combination, this method can solve port isolation and port amplitude balance problem basically simultaneously to obtain more reliable or more accurate performance.

Though disclosed herein is example embodiment, it will be understood by those skilled in the art that the many variations according to this instruction are possible and fall within the scope of the claims.Therefore, except within the scope of the claims, the utility model is unfettered.

The cross reference of related application

The application is people's such as Donald Ingram U.S. Provisional Patent Application No.61/991,950 priority based on be entitled as " Path Balancing in Radio Frequency Distributor ", the invention people that 35U.S.C. § 119 (e) requires to submit on February 15th, 2012.This U.S. Provisional Patent Application No.61/991,950 whole disclosing specifically is incorporated into this by reference.

Claims (12)

1. distributor that is used for radio frequency RF signal comprises:

A plurality of power paths are configured to the signal in the RF scope is sent to a plurality of output ports from input port;

A plurality of amplifiers, being disposed in the corresponding power path and being configured to send described signal at the first direction from described input port to described a plurality of output ports provides reverse isolation in the second direction opposite with described first direction simultaneously;

A plurality of attenuators are disposed in the corresponding power path and are configured to the variable amount of described signal attenuation in each power path; And

Controller is configured to change attenuation in response to triggering input.

2. distributor as claimed in claim 1 also comprises a plurality of splitters, is configured to described signal is assigned in described a plurality of power path.

3. distributor as claimed in claim 1, wherein, described a plurality of splitters comprise the two-way splitter of cascade, each two-way splitter its separately output place have directed amplifier.

4. distributor as claimed in claim 1 also comprises controller, the described attenuation that this controller control is provided by each attenuator.

5. distributor as claimed in claim 4, wherein, described controller comprises on-site programmable gate array FPGA.

6. distributor as claimed in claim 4, wherein, described controller comprises state machine, this state machine changes in response to the state of described triggering input control attenuator.

7. distributor as claimed in claim 4, wherein, described controller is controlled described attenuation according to the predetermined value that generates by the electrical characteristics of measuring described power path in calibration process.

8. distributor as claimed in claim 7, wherein, described predetermined value is indicated the characteristic that depends on frequency of described attenuator.

9. distributor as claimed in claim 1, wherein, the resolution that described attenuator is configured to 1/8 decibel provides decay.

10. distributor as claimed in claim 1, wherein, described signal is the test signal that is generated by network analyzer.

11. distributor as claimed in claim 1, wherein, each power path comprises directional coupler, is configured to allow carry out the two-way communication of while basically with described a plurality of output ports.

12. distributor as claimed in claim 1, wherein, each power path also comprises calibration switch, is configured to will be routed to receiving port from the signal of described input port during calibration operation.

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