[introduction]In going 10 years, mobile and wireless data grows quickly, make operation business all the more needs technology of new frequency Duan Hexin pressingly, in order to satisfy an user the demand to wireless data capacity. This kind of demand promoted the development of wireless technology not only, also increased to increasing model radio frequency (the demand of RF) filter technology, reduce systematic interference in order to help, enlarge RF to cover range, enhance receiver performance, promote concomitant character.

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In going 10 years, mobile and wireless data grows quickly, make operation business all the more needs technology of new frequency Duan Hexin pressingly, in order to satisfy an user the demand to wireless data capacity. This kind of demand promoted the development of wireless technology not only, also increased to increasing model radio frequency (the demand of RF) filter technology, reduce systematic interference in order to help, enlarge RF to cover range, enhance receiver performance, promote concomitant character.

The working principle of a filter of RF of content general introduction, and all sorts of technology version that use in the application nowadays. Introduce a few basic truth about filter above all, and the profit that they bring.

About the ABC of RF filter

Will understand these significant filter technical terms and concept first.

? Damply: The amplitude loss that signal produces after passing RF filter, normally with decibel (DB) is measured for the unit. When citing beyond filter bandpass limits, it also is called to restrain.

? Cut off: Filter responds the corresponding point when reducing 3dB.

? Insert loss: The signal power loss in the target bandpass of filter.

? Segregation: signal each other are separated, arise in order to prevent between them needless alternant. For example, you may be kept apart send signal and receive signal, in case their generation is alternant.

? Bandpass: Signal is passed, but the area that does not have attenuation almost.

? Q factor: The abbreviation of quality factor, it is to point to in every oscillation cycle, the rate between memory energy and loss energy. Those who be used at measuring syntonic circuit is alternative.

? Ripple: The difference of loss is inserted in bandpass.

? Alternative: Specific to filter is passed or be being restrained frequency (opposite at central frequency) of ability measure. It is to show in the center with filter frequency differs commonly optionally the loss that the node place that assigns frequency produces.

? Block belt: Restrain outside the area that filter reachs place to need (the decibel number that wants by place shows) when answered frequency paragraph.

Graph 1: Typical RF filter is answered

The spare frequency part in filter purify signal, maintain requires frequency bandwidth at the same time. Graph 2 show 4 kinds of basic filter to means receives or check signal in order to differ:

? Low connect filter: Allow to be passed under all frequency of a certain frequency, prevent all and other frequency (and connect high opposite)
? Connect filter high: Allow prep above all frequency of a certain frequency are passed, prevent all and other frequency (and low opposite)
? Take a filter: Allow interpose to be passed at all frequency between two frequency, prevent all and other frequency (and belt block is opposite)

? Frequency paragraph restrain filter (also call take block or defect wave filter) : Stop take to heart all frequency between two frequency, allow all and other frequency to pass (and belt opposite)

Graph 2: Basic RF filter and answer

The comparison of filter technology

What the basis applies is different, the structure of filter is different also. The difference with RF filter the commonnest technology depends on dimension, cost and function. The structure of filter is the main factor that causes these difference. It is give typical examples of structure of filter of a few RF below:

? Acoustics filter: A kind of filter, can satisfy low frequency and tall frequency (be as high as 9GHz) , can satisfy below a little special situation be as high as 12GHz frequency. Its volume is minor, offer admirable function and cost combination, in order to satisfy complex filter requirement. Acoustics filter is business applies with RF microwave (for example mobile phone, WiFi and GPS of global location system) in the commonnest filter structure.

? Cavity filter: One kind is used in the filter in infrastructure application only. It can achieve good performance below reasonable cost, but volume is larger than acoustics filter.

? Schism type inductance – capacitance (LC) filter: Cost of a kind of construction is low, the filter with function and moderate volume. LC component the form with printing a structure is occasionally compositive go up in substrate, call parts of an apparatus of compositive type passive (IPD) . LC filter also can pass schism type watch to stick parts of an apparatus (SMD) component comes true.

? Filter of monomer type pottery and porcelain: A kind of cost and function all prep above is multilayer the filter of filter of pottery and porcelain. Its volume is larger also, do not suit to be used at shift application.

? Multilayer filter of pottery and porcelain: The one filter of low cost in the paragraph, function and LC filter comparative. Its take up area normally relatively reasonable, but ply is bigger, make its cannot be used at some application.

? Filter can be designed use at satisfying a variety of requirements. Although they use identical basic circuit configuration, but when be being used at satisfying different level by the design when circuit, circuit value can differ somewhat. For instance, satisfy the ripple inside the belt when need, transfer to boil finally with the rapiddest rate fall, restrain outside top band when waiting for a standard, can cause different circuit value.

Type of understanding pressing report is acoustics filter

To a lot of application nowadays, the filter technology of first selection is filter of the type that suppress report. These RF filter are bulk the solution with cabinet, efficient economy, use in a lot of commerce, military affairs and science application.

Piezoelectric effect is a kind of reversible physics phenomenon. Crystal material is in electricity is produced when mechanical stress, vice versa. Should bring to bear on when electric field or voltage, crystal can have the drawing of little scope. Press the electric energy of mechanical stress translate into that electric data will bring to bear on, also can stress of machinery of electric energy translate into.

Two kinds of acoustics filter are offerred on market, it is exterior sound wave respectively (SAW) and body sound wave (BAW) .

If the graph is shown 3 times, SAW and BAW filter can divide it is two kinds: Ladder type and bar format. Ladder type filter has very tall inhibition around bandpass, but function is controlled outside the belt very poor. Bar format filter is offerred restrain outside nice area, inferior inhibition is offerred around bandpass. And ladder type – the mixture configuration of bar format is being restrained and bandpass is restrained implementation is eclectic between function.

Graph 3: SAW and BAW configure a design

SAW filter

SAW filter application is wide, very mature. It is transverse transmit high frequency wave. If the graph is shown 4 times, use in acerbity lithium of quartz, Tantalum (LiTaO3) or niobium acerbity lithium (the crisscross metal fork that founds on the substrate suppressing report such as LiNbO3) points to type transducer (IDT) , report input signal changeover is sound wave. SAW filter rate is slow, a lot of wavelengh of IDT are crossed in can be being used at getting used to dinky parts of an apparatus.

Graph 4: Basic SAW RF filter

A crucial dominant position of SAW depends on, it can optimize the standard filter application that is used at 600-1900MHz. The low 5G frequency that it can satisfy 600MHz not only paragraph, and in 1, 5, 8, frequency of 13 low mobile phones paragraph and GPS frequency paragraph fall to also show scene, and economy is efficient.

To achieve 1900MHz above, we are used statified SAW technology, for example technology of small loss resonator (LRT) , filmy SAW (TF-SAW) , exceed SAW or performance is extremely high (the SAW of IHP) . These technologies make multilayer SAW can achieve 2.7GHz, can use Yu Zhonggao frequency paragraph application. When prep above 2.7GHz, drop of SAW filter optionally. But, when the effectiveness of SAW filter ends, BAW filter (this chapter can undertake introductory later) begin to produce effect.

Temperature compensates SAW

In innovation of technology of a lot of SAW, a kind of temperature compensates SAW (TC-SAW) . TC-SAW uses vulcanize countervail layer to avoid to heat up drift, if pursue,5 are shown. Because have taller temperature stability, its function wants excel standard SAW.

Compare with the traditional filter that is based on SAW and diplexer photograph, TC-SAW parts of an apparatus is compositive go up in acerbity lithium of single crystal niobium, and IDT electrode embedded 2 oxidation silicon (in SiO2) layer, raised TCF and quality factor.

Graph 5: SAW and TC-SAW are compared

Want to use temperature coefficient on SAW, need points to fork type transducer (IDT) and change keeps apart any environmental temperature to come. Want to realize this kind of segregation, need uses SiO2 layer to cover SAW construction, still need additional nitrogen to change silicon layer occasionally, if pursue 5 on the right side of be shown.

TC-SAW improves filter performance, in order to answer the frequency with LTE and strict 5G paragraph allocate, and go up link and facilities of high power user (the carrier wave of HPUE) is aggregate (CA) . These improvement include lower insertion stability of the character side loss, steeper skirt, temperature, taller power source wear, wider bandwidth frequency range, taller degree of linearity, smaller size and compositive. To realize these character, need uses higher Q factor and lesser frequency temperature coefficient (TCF) .

Multilayer SAW

In traditional SAW substrate structure, surface of sound wave edge travels, a few wavelengh are achieved below electrode, mode of radiate of body sound wave is to appear in the depth of substrate. This meeting causes leak of body sound wave, make Q factor, TCF and coupling are reduced.

One of methods that reduce this kind of leak are to found new multilayer structure or be found TC-SAW change model, if pursue,6 are shown. Increase this extra SiO2 layer to be able to provide a significant benefit below in the layer that suppress report and functional layer surface: Introduce the SAW that travels in the surface the layer that suppress report and functional layer. This meeting is acoustics energy limitation near the surface, improve TCF and Q factor thereby.

Graph 6: Multilayer the comparison of SAW and SAW

There is the SAW filter of a few kinds of types on market. They are called SAW, TC-SAW and multilayer SAW, also be called to guide type SAW, LRT-SAW, TF-SAW, Ultra-SAW and IHP-SAW. They belong to SAW sort, one increases between substrate and functional layer, for example SiO2, if pursue,6 are shown. In this book, we call this kind of type SAW.

Multilayer the function of SAW wants filter of SAW of prep above standard. In some frequency paragraph in, multilayer the function of SAW can rival BAW filter, next we can discuss this.

Multilayer the material suppressing report that goes up in order to distributing in isolator is SAW technology foundation. Be in multilayer in SAW, vulcanize countervail mechanism comes from substrate directly, is not to come from electrode surface.

Next watches compared the different characteristic of technologies of all sorts of filter of acoustics SAW RF.

BAW filter

BAW can be used at replacing SAW. BAW filter supports 1.4 to 9GHz frequency limits.

Besides the structure, the main distinction of BAW and SAW depends on filter going back on his word to press electric data with what use. BAW filter uses much brilliant nitrogen to melt aluminium, have taller coupling coefficient and taller velocity of wave.

The acoustics energy density of BAW filter is very high, and its structure can catch sound wave well, because this can realize extremely small loss. In addition, compare the filter kind with the other right measure that uses below microwave frequency, factor of their realizable Q is higher. Can come true to restrain and insert loss performance outstandingly so, edge is being connected in crucial area also is such.

BAW filter offers lower insertion loss, conduce to the battery service life in lengthening smartphone application. BAW still is applied to go up the space is very short application between link and link of be issued to lower levels, and in the photograph adjacent frequency that arranges cheek by jowl paragraph in very tall to attenuation requirement application.

Differ with SAW filter, the sound wave in BAW filter is perpendicular transmission. If the graph is shown 7 times, crystal regards resonator use quartz as substrate. Quartz the metallic method of two side arouses coping and bottom sound wave, sound wave rebounds after all from coping ministry surface, form standing wave. The quality of the ply of flat and electrode decided the frequency of resonance happening. In BAW filter effective tall frequency falls, the layer that suppress report must have a few micron only thick, this asks resonator structure is with carrier wave substrate is a bottom, use film form sediment accumulating and accurate treatment are formed.

Graph 7: Basic BAW RF filter

In the filter of this kind of type, arrive to prevent sound wave to escape in substrate, the layer that meeting pile stiffness and density change alternately will found Prague acoustics reflector. Compose builds the parts of an apparatus that go out to be called to originally carry resonator (SMR) BAW, if pursue,7 are shown. Prague reflector is formed by multilayer and alternant material, the refractive index of these material each are not identical.

There basically is the BAW filter of two kinds of types on market, if the graph shows 8 times: Solid carries resonator (SMR) BAW and resonator of sound wave of body of much brilliant film (FBAR) .

Graph 8: Of BAW filter technology sectional quite

From the point of technical angle, the biggest distinction depends on substrate, and the cavity between substrate and rock-bottom electrode. The basis issues a list, the temperature compensation performance that can see pile layer BAW is optimal.

Some companies can use his brand name to point to acting FBAR or BAW technology, but they vest in BAW or FBAR these two kinds of technologies. For example, XBAW is another kind of FBAR, exceeding BAW is another kind of BAW. XBAR is technology of BAW of a kind of Jian Bo, have the character of a transverse coupling; But, this technology still is in phase of research and development, have not put into production…

Length of be confined to, the wonderful content such as coefficient of factor of the temperature coefficient of more concerned filter, Q, coupling will be in ” technology of exploration RF filter (below) ” continue to discuss, must advertent our push civil oh ~

The article reprints from: Qorvo semiconductor

 

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