About those works that radio frequency chip checks

 

Insert loss, segregation to spend, …… of switch time, harmonic which be pain spot of test of radio frequency switch?

How to check after all insert loss, segregation to spend compare with standing wave, actually very simple!

 

Switch time Switch Time

 

What is switch time?

 

Switch time (what Switch Time) or switch time point to is switch guides from “ change is a ” condition “ ends ” condition perhaps ends from “ the time that ” status change guides for “ place needs a ” position. Specific will tell is to point to receive passageway switch to command from DUT, achieve the of 90% time that full range is worth to the power in the signal on the channel that is reached by switch.

 

Graph 1: Switch time tests

 

Be aimed at the test at the lab, according to telling regular meeting the consideration uses oscillograph of tall bandwidth high speed to have a test. Checking a method is get DUT to control signal and radio frequency signal at the same time in two passageways, measure what DUT controls signal to jump change the time that edge and radio frequency signal arrive at corresponding power to be worth hour is wrong.

 

 

To oscillograph, an index that cares most is bandwidth. Bandwidth was described arrive from bougie or front of test clamping apparatus ADC, loss of input signal amplitude most hour, can adopt the frequency range of imitate front. Bandwidth is defined to be input of wave of a sine, after passing oscillograph, measure its are primitively amplitude the frequency of 70.7% , also call – 3dB dot. Below most circumstance, we suggest the bandwidth of oscillograph is the signal that be measured in of highest frequency heft 2 to 5 times, captured signal extent error the influence is reduced the smallest () of frequency of bandwidth requirement =(2~5)* .

 

Check to the test and verify of lab switch time of radio frequency switch, the time that need has DUT controls signal and signal of output of radio frequency switch to achieve corresponding power to be worth hour is wrong, accordingly to both, it is among them crucial that rise time is measured.

 

Graph 2 showed limits of a 500MHz measures gauss model rank jump answer. When rank jumping corresponding highest frequency is 4 times at instrument bandwidth (gules curve) , we see basically be oscillograph only rank answer and jumping is not input signal rank jump answer. There is quite big error in because this is having rise time,be being measured (416%) . The signal that be measured and oscillograph (maize curve) when having identical bandwidth, still can cause serious error (40% ) . We can see, be being measured the 1/3(green curve that signal frequency is oscillograph bandwidth) when, result of rise time test will be relatively accurate (only 4.4% ) . So a very good experience method is a choice one is highest frequency at least the oscillograph of the imitate bandwidth of 3 times.

 

Graph 2: 500MHz bandwidth oscillograph to differring rank jump response curve
 

NI is offerred choose to a variety of oscillograph that are as high as 5GHz bandwidth, resolution to go to 14 from 8 from 400MHz, satisfy the test task below different application. Cooperate the seesaw pattern face plate with powerful function, test of sex of implementation lab test and verify undertakes the interface is debugged friendlily, match at the same time the API that a variety of languages support, be like LabVIEW, c, python, the automation that implements fast lab checks development.

 

 

Tall bandwidth oscillograph is used to be able to undertake fast weaveform is examined in test of lab test and verify reach rise time computation, but this method produces a test in the quantity in although can satisfy test requirement, but the cost in facing a quantity to produce and the requirement that test time to go up, the oscillograph of the tall bandwidth that the price does not poor is a huge expense on systematic cost; At the same time the radio frequency output of DUT is designed in systematic jumper, besides wanting to receive incident frequency instrument, still need additional receive output oscillograph to go up, what will add a system so is complex degree. Accordingly, the test is produced in the quantity in, we can consider other design method.

 

When the area of a room when undertaking switch produces a test, we use the NI Digital Pattern that takes PPMU function to be based on the digital instrument PXIe-6570 of vector, cooperate signal of NI VST vector to send and receive appearance to undertake the system is designed. PXIe-6570 is included have spark and the deepness of Pattern sort board carry memory. Through be based on the Pattern of vector, it can go to chip process designing foregone condition. And the most important is, those who was based on the test platform of PXIe bus line to design high accuracy, small delay time is synchronous mechanism surely, such index got very good settlement to the problem that synchronism sparks between two module.

 

 

NI was offerred for PXI and PXI Express box time and synchronous solution. Newest PXI Express undertook reform to PXI platform, in reservation backward compatible while, in the light of measure I/O equipment, provided more powerful than PXI-1 synchronous function. Particular system now:

 

● PXI Express withheld the clock of 10 MHz backboard in original PXI standard, and Chan Duan PXI sparks the PXI star form that bus line and length match sparks signal.

 

● PXI Express still increased 100 MHz to differ time-sharing bell and form of poor cent star to spark on backboard, offer the buildup synchronous precision that fights noise ability and industry to precede (the defer between the module that is 250 Ps and 500 Ps respectively is poor) . NI times and synchronous module makes full use of in PXI and PXI Express box advanced time and spark technical advantage.

 

Graph 3: Be based on the time and synchronous mechanism of PXI
 

Test system is produced to be designed in the quantity, we also made full use of PXI platform sparks the tall accuracy of bus line, small delay time is characteristic. If the graph is shown 10 times, the digital instrument PXIe-6570 that is based on vector is in give out control jussive at the same time, produce an incident to spark pulse, this pulse conveys through PXI bus line VST, spark VST begins to collect radio frequency signal. In the system one by one checks the extent that sampling of radio frequency signal is worth, more attainable the sampling dot that the first extent satisfies a requirement, and begin hour as a result of what radio frequency signal collects drive the hour that passes switch namely, with contented requirement sampling dot time difference is multiplied can get switch time with sampling cycle.

 

Carry such kind the reusability of instrument of will great promotion, and do not need additional oscillograph to have a test, reduced test cost, and also reduced the time of the switch between the instrument, promotion checks efficiency.

 

Graph 4: The switch time of the digital instrument that is based on vector and VST tests

 

For harmonic travel nonlinear parts of an apparatus is caused, can bring about in output power produces higher than emiting frequency below multiple frequency. Because a lot of wireless standards had strict regulation to the radiate outside the belt, whether did so the engineer can evaluate RF through measuring harmonic or FEM violate these radiation requirements.

 

The specific means that measures harmonic power depends on normally the anticipation of RF utility. To the equipment of parts of an apparatus such as general RF, harmonic measures need to use successive wave signal to come incentive DUT, measure the power of the harmonic of generates different frequency. Additional, measure harmonic power to need special attention normally the bandwidth of signal is characteristic.

 

 

Use successive wave drive to measure harmonic to need to use signal generator and signal analyzer. To incentive signal, need uses a signal generator to make the successive wave that has place to need to output power and frequency. After the signal generator generates incentive signal, signal analyzer is in multiple output power at be being measured below the frequency of input frequency. Common harmonic is measured have harmonic and 5 harmonic 3 times, be in respectively 3 times fall with the incentive frequency of 5 times undertake metrical.
 

 

 

RF signal analyzer offerred a variety of measurement technique to measure the output power of harmonic. A blunt method is the anticipation that moves analyzer to harmonic frequency, hand-in-hand travel peak value is searched in order to find harmonic. For example, if want to measure 3 harmonic when generating 1GHz signal, criterion 3 the frequency of harmonic is 3GHz.

 

Another kind of method that measures harmonic power is use signal analyzer 0 exhibit frequency (Zero Span) mode undertakes metrical in time domain. The signal analyzer that configuration is the 0 mode that exhibit frequency undertakes a series of power are measured inside the belt effectively, show the result with the function form of time come. Here mode falls, the power that frequency differs in choosing a window can be measured on time domain, the extraction that uses the buy inside signal analyzer is average the function has consideration.

 

Besides, set bigger power input commonly in the test condition of chip of radio frequency switch, after because this needs amplifier of power of adscititious radio frequency,having the power of the signal generator enlarge, give be measured parts of an apparatus.

 

 

The test is produced in the quantity in, signal analyzer is opposite taller, because this still can use vector signal send and receive module of appearance collocation high power to come true, the biggest change answer the instrument that a place checks to use before using.

 

The signal of only news radio frequency that VST generates, the high power module of classics NI (NI 5534) enlarge, output power can amount to 38dBm, the signal after enlarge achieves the parts of an apparatus that be measured via the low wave that connect filter, the output signal filter of the parts of an apparatus that be measured is divided advocate after frequency composition, the harmonic part that remain sends NI high power module through assisting switch (NI 5534) receive method, classics attenuation evacuation enters VST.

 

Intermodulation is lack fidelity IMD

 

To understand IMD, we need to review nonlinear polyphonic signal of the system is academic. Although incentive signal meets Chan Yin to be in in every multiple of this signal frequency,produce harmonic action, but what polyphonic signal arises is nonlinear child need just is met in wider frequency range appear.

 

If the graph is shown 5 times, DUT output carries 2 rank lack fidelity child appears in input signal frequency every diploid frequency place. F2 – F1, 2f1, f1 + F2, the lack fidelity production that 2 harmonic that contain every input news with the lack fidelity product that 2f2 place produces and two inputs frequency lead addition and photograph to decrease frequency to be in.

 

Graph 5: IMD theory
 

3 rank of lack fidelity description is signal of first-order foundamental tone mixes every 2 rank the interaction between lack fidelity child. In fact, learn computation through number, can see two specific 3 rank lack fidelity below the frequency that gives to be close to fundamental frequency now. With actual application is exemple, when DUT sends modulation signal, 3 rank lack fidelity as the place that lack fidelity occurrence in the vicinity of is interested in frequency band inside the belt.

 

What IMD measures a description is foundamental tone and photograph adjacent 3 rank lack fidelity the rate with the poor power between, express with DB. A when IMD measures main feature is first-order and 3 rank lack fidelity the power between is compared depend on completely the absolute power n of every sound.

 

In the linear work area of a lot of parts of an apparatus, first-order sound and 3 rank the rate of lack fidelity child often very tall. However, as the addition of foundamental tone power input, 3 rank lack fidelity child also increases subsequently. Actually, every increase the power of foundamental tone 1 DB, lack fidelity child can increase intermodulation 3 DB.

 

Theoretic, as a result of 3 rank the can raise speed than foundamental tone power rate of power of lack fidelity child is rapidder, the signal of two kinds of types is so final on power n equal, if pursue,18 are shown. Come up from theory tell, foundamental tone and 3 rank the dot with equal power of lack fidelity child is cut breakpoint, this the dot also calls 3 rank cut to nod (TOI or IP3) .

 

 

Intermodulation is lack fidelity (IMD) nod with 3 rank cut (TOI) it is the face plate before NI-RFSA software (SFP) inside buy measures a function. When undertaking these measurement, can be the frequency setting of signal analyzer it is central frequency with two foundamental tone, can see noise of prep above this locality in order to ensure 3 rank lack fidelity child. On NI-RFSA SFP the choice detects sound, generate measure an outcome. The power difference that NI-RFSA SFP can distinguish foundamental tone automatically and 3 rank the power of lack fidelity child is poor, show correct measurement result. About the more information of analyzer of PXI RF signal, visit Ni.com/rf/test please.

 

 

Graph 6: Every increase power of foundamental tone signal 1 DB, 3 rank power of lack fidelity child increases 3 DB

Actually, IP3/TOI is the outcome that computational earning and rather than measures income. First-order child and 3 rank the power between child increases comparing is 3:1, the formula below benefit in order to can be calculated an IP3.

 

 

TOI is the main index that measures performance of radio frequency front, depend on because of IMD rate power n. The measurement of TOI combines the element of IMD function and look of absolute power n, show performance through a number.

 

 

Measure theory according to IMD, carry out this to measure signal of drive of need double sound. In great majority application, the first selection method that deploys signal of double sound drive is join RF signal generator to RF power is combined implement, if pursue,13 are shown.

 

Graph 7: IMD measures need join to be combined to power implement two signal generator

Because IMD is a kind of common measurement means, a lot of RF signal analyzer are had inside buy measures a function to measure IMD or IMD/TOI. In fact, NI-RFSA SFP can detect automatically foundamental tone and 3 rank lack fidelity child, calculate an IMD comparing.