Impedance matchs have two kinds, one kind is to pass through change impedance force (Lumped-circuit Matching) , another kind is the wavelengh that adjusts transmission line (Transmission Line Matching) .

 

Want to match a group of circuitry, be worth bit ladener impedance above all, except the characteristic impedance with transmission line the value comes normalization, delimit numerical value on Shimisitu next.

 

PCB uploads the electronic model sketch map that loses a line

 

Change impedance force

 

Rise capacitance or inductance and laden series connection, can increase or reduce laden impedance cost, the dot on chart is met ambulate along the circle that represents real resistance. If capacitance or inductance ground connection, above all the dot on chart is met center of to in an attempt to rotates 180 degrees, just ambulate along resistance group next, rotate along the center again 180 degrees. Till resistance becomes,repeat above method 1, can turn into impedance force directly 0 finish match.

 

Impedance matchs: Say simply even if ” of “ character impedance is equal to ” of “ laden impedance.

 

Adjust transmission line

 

Order lengthen transmission line to origin by laden dot, the dot on chart can ambulate with anticlockwise direction along picture center, till walk along resistance to go up for the circle of 1, can add capacitance or inductance to adjust impedance force for 0, finish match.

 

Impedance matchs to transmit power big, will tell to a power source, its internal resistance is equal to sheet when load, output power is the greatest, right now impedance matchs. Most high-power transmits theorem, if be high frequency word, do not have reflection wave namely. To common broadband amplifier, output impedance 50Ω , power transmits the need in circuit to consider impedance to match, if signal wavelengh is more than cable length far,can be, namely cable grows negligible word, with respect to beardless consideration impedance matched. Impedance matchs is to point to when energy is transmitted, requirement load impedance wants and the diagnostic impedance of transmission line is equal, right now transmission won’t produce reflection, this shows all energy were absorbed by load. There is energy loss in transmit conversely. When wiring of high speed PCB, to prevent the reflex of signal, ask the impedance that is circuit is 50 ohm. This is about number, set coaxial cable base band commonly 50 ohm, frequency band 75 ohm, it is 100 ohm to skeining thread, just take whole just, go to the lavatory to match.

 

Impedance looks from literal as different as resistor, having word of a block only among them is identical, and do another fight a word? Say simply, impedance is resistor adds reactance, just call impedance so; A bit ground says distribution, impedance is capacitive reactance of resistor, report and electric inductance on vector and. In the world of dc, the object is called resistor to voltaic obstructive action, all material on the world have resistance, the size diversity that is resistance only just. The material with little resistance calls good conductor, the material with very great resistance calls blame conductor, and the superconductor that says in high-tech domain recently, it is the thing of practically negligible of a kind of resistance. But meet besides resistor in the domain of alternating current beyond block up electric current, capacitance and inductance also are met the flow of block up electric current, this kind of action is reactance with respect to what say, meaning resist namely voltaic action. The reactance of capacitance and inductance calls report capacitive reactance and electric inductance respectively, abbreviation capacitive reactance reachs inductance. Their unit of measurement and resistor are ohmic euqally, and the size that its are worth matters with the frequency of alternating current, frequency heals Gao Zerong is fought more small inductance heals big, frequency heals low criterion capacitive reactance heals big and inductance heals small. Capacitive reactance of this dispatches from foreign news agency and electric inductance still have the problem of phasic angle, have the relation on vector, accordingly ability can say: Impedance is resistor and reactance on vector and.

 

Impedance matchs is to show laden impedance and impedance of incentive source interior are mutual comfortable match, get most the status of a kind of job that high-power outputs. To the circuit of different character, matching a requirement is different.

 

In pure resistor circuit, when laden resistor is equal to incentive source internal resistance, output power to be the biggest, status of this kind of job is called match, call otherwise break match.

 

When when incentive source internal resistance is fought and laden impedance contains reactance component, to make load gets most high-power, laden impedance and internal resistance must be satisfied control a concern in all, namely resistor component is equal, reactance component is only numeric and equal and the symbol is contrary. This kind matchs a condition to call clutch in all match.

 

Shimisitu (Smith Chart) is a chart that is used at electric machinery and electronic engineering, basically use at the impedance of transmission line to match. A transmission line (the impedance of Transmission Line) (length of physics of Impedance) meeting therewith and change, should design an impedance to match (the circuit of Impedance Matching) , need adopts the computational program of many heavy and complicated, shimisitu’s characteristic is dispense with program of a few computation.

 

This chart is • of general of You Fei benefit Smith (Phillip Smith) invented 1939, he works in RCA company of the United States at that time. Smith ever had said, “ can use slide rule in me when, the correlation that I convey maths to go up to coming with chart means very have fun at. ”

 

Of Shimisitu depend on basically calculating type below

 

 

The reflection coefficient that the Γ in the center represents its line (Reflection Coefficient) , namely the S11 in S-parameter, ZL is to put in one laden value ‘s charge, namely ZL / Z0. In the center, ZL is the laden value of circuit; Z0 is the characteristic impedance value of transmission line, connect regular meeting to use 50Ω .

 

The circular line in chart fights the real value of force on behalf of resistor, namely resistance, the horizontal line among and mix up come loose downward the empty that the clue that give fights force on behalf of resistor is numeric, be in by capacitance or inductance namely the obstruction of high frequency generation leaving place, in the center up is plus, those who be down is negative number. Chart most the dot among (1+j0) delegate already matched (the resistor of Matched) is numeric (ZL) , the value that at the same time its reflex coefficient can be 0. The length that the brim of chart reflexes coefficient on behalf of its is 1, namely 100% reflex. The angle that reflexes coefficient in the digital delegate of graph edge (0-180 is spent) with wavelengh (by 0 to half wavelengh) .

 

Having a few chart is be worth with admittance (Admittance) will express, rotate version of afore-mentioned impedance value 180 degrees can.

 

Since after having the computer, the utilization rate of this kind of chart subsequently and below, but still commonly used will represent specific data. Say to reading the student of electromagnetism and microwave electronics to come, solving textbook problem very practical still, accordingly Shimisitu still is important education appliance up to now.

 

In paper, the result of measurement instrument also regular meeting expresses with Shimisitu.

 

One, the research that impedance matchs

 

In high-speed design, the matchs to mattered to signal quality actor of low quality of impedance. The ability that impedance matchs but art it is rich diversity in order to say, but how does ability compare rational application in particular system, need measures the factor of many respects. For example we are in in the system in the design, a lot of those who use is a source paragraph string match. Match to the need below what circumstance, use what means match, why to use this kind of means.

 

For example: Of poor cent match majority to use terminal to match; Clock uses source Duan Pi to match;

 

1.1, series connection terminal matchs

 

The academic jumping-off place that series connection terminal matchs is in signal the source carries impedance to fall under the condition of impedance of transmission line feature, be carried in the source of signal and string together between transmission line receive R of a resistor, the outputs impedance and transmission line diagnostic impedance photograph that makes the source is carried matchs, restrain the signal that carries reflection to come back from load to happen to be reflexed again.

 

The signal after series connection terminal matchs transmits have the following characteristic:

 

The A, action that matchs resistor as a result of series connection, the with its extent 50 ％ when drive signal travels travel to laden end;

B, signal is close to ＋ in the reflection coefficient of laden end 1, because this reflexes the extent of signal,be close to the 50 ％ of primitive signal extent.

Signal of C, reflex and source carry the signal overlay of transmission, the range of the signal that makes laden termination gets and primitive signal is approximate and same;

D, laden end reflexes signal to carry transmission to the source, after arriving at a source to carry, be matched resistor is absorbed;

After signal of E, reflex arrives at a source to carry, the source carries drive electric current to fall for 0, until the next time signal is transmitted.

 

Opposite paralell connection matchs for, series connection matchs not to ask signal driver has very large voltaic drive capacity.

 

The principle that chooses series connection terminal to match resistance is very simple, the outputs impedance the sum and transmission line feature impedance that asks to match resistance and driver namely is equal. The output impedance of good signal driver is 0, actual driver always has smaller output impedance, and when the n in signal produces change, output impedance may be different. For instance power source voltage is the CMOS driver of ＋ 4.5V, typical when low n output impedance is 37Ω , typical when tall n output impedance is 45Ω[4] ; TTL driver and CMOS drive are same, the n size that its output impedance to be able to follow signal changes and change. Accordingly, to TTL or CMOS circuit, have a very correct distribution block impossibly, can consider eclectically only.

 

Chain record pictures attacks signal network of the structure does not suit to use series connection terminal to match, all load must receive the terminal of transmission line. Otherwise, the weaveform that receives the load among transmission line to be accepted can resemble a plan 3.2.5 in the voltage weaveform that C nods is same. Can see, load of period of time carries signal extent to be the half of primitive signal extent. Apparent at that time signal lies errant and logistic condition, the noise tolerance of signal is very low.

 

Series connection matchs is the most commonly used terminal matchs a method. Its advantage is power comsumption small, won’t bring additional dc load to driver, also won’t introduce additional impedance between signal and ground; And need component of a resistor only.

 

1.2, shunt-wound terminal matchs

 

The academic jumping-off place that shunt-wound terminal matchs is in signal the source carries the condition with very small impedance, the diagnostic impedance photograph that inputs impedance and transmission line through increasing shunt resistance to make load is carried matchs, achieve eliminate load to carry catoptric end. Cent of type of solid reveal one’s true features is only resistance and double resistor two kinds of forms.

 

The signal after shunt-wound terminal matchs transmits have the following characteristic:

 

Signal of A, drive is approximate travel with transmission line of full range edge;

All B, reflex are matched resistor is absorbed;

The signal range that the signal extent that C, laden termination gets and source end deliver is approximate and same.

 

In effective circuit system, the input impedance of chip is very tall, for form of because this is right only resistance, the shunt resistance of laden end is worth must the diagnostic impedance close with transmission line or equal. Assume the diagnostic impedance of transmission line is 50Ω , criterion R value is 50Ω . If the tall n of signal is 5V, criterion the static electric current of signal will achieve 100mA. The drive capacity as a result of typical TTL or CMOS circuit is very small, the paralell connection of this kind of only resistance matchs means to appear in these circuit rarely.

 

The paralell connection of double resistor form matchs, also be called the terminal austral Daiwei to match, the voltaic drive capacity of the requirement is smaller than only resistance form. Because the diagnostic impedance photograph of the shunt-wound value of two resistor and transmission line matchs,this is, every resistor compares the diagnostic block the Chinese People’s Anti-Japanese Military and Political College of transmission line. Considering the drive ability of chip, the choice of two resistance must follow 3 principles:

 

The diagnostic impedance of the shunt-wound value of ⑴ , two resistor and transmission line is equal;

⑵ , with resistance of power source connective cannot too small, lest signal is electric current of the drive when low n,pass big;

⑶ , with ground connective resistance cannot too small, lest signal is electric current of the drive when tall n,pass big.

 

It is simple that shunt-wound terminal matchs an advantage easy travel; The defect of clearly is to be able to bring dc power comsumption: Of the dc power comsumption of only resistance means and signal occupy sky comparing close together and relevant; Double resistor means no matter signal is tall n or low n,have dc power comsumption. Do not apply to the expensive to power comsumption requirement system such as batteries power supply system consequently. Additional, only resistance means is as a result of drive capacity issue in system of general TTL, CMOS without application, and double resistor means needs two component, this is right of PCB board the area raised a requirement, because this is unwell and operable,spend printed circuit at high density board.

 

Still have of course: AC terminal matchs; The voltage clamp that is based on diode wait for a prescription form.

 

2, regard the transmission of signal as tube sends water to irrigate a flower

 

2.1, the layer of digital system board line (Signal Line) in, when the transmission of signal of occurrence square wave, but will the hypothesis makes tube (Hose) send water to irrigate a flower. One aspect of the matter grasps place pressurization to make its shoot a water column at the hand, another termination is in faucet. Use the force that control when the location that grasp a canal apropos, and the cannon-shot that lets water column is aspersed correctly fall in target zone time, criterion bestow suffers both fulfil a mission all joyous and smoothly, be not the small achievement of a kind of handy?

 

2.2, once exert oneself to do sth. excessive water is noted,shoot Cheng Taiyuan however, not only rise high into the air crosses a target to waste water natural resources, because of,return a likelihood even puissant and hydraulic nowhere drain, source of come-and-go of as a result rebounds those who cause tube to go up from bibcock flounce off! Not only setback of task failure be overflowing with, and careless mistake of big still disclose all over the face fabaceous fancy suiting!

 

2.3, conversely, should grasp the extruding of place cannon-shot of insufficient as a result is too close person, cannot get wanted result all the same. Going too far as bad as not going far enough all is not place desire, only everyone is happy of proper ability fit in exactly with one’s wishes.

 

2.4, afore-mentioned simple trifling matters of everyday life, can using in order to show square wave (Square Wave) signal (Signal) in multilayer board transmission line (Transmission Line, department by layer of line, medium, reach ground connection layer 3 person place is comprised jointly) in what what undertake is fast and deferent. Right now but transmission line (common person have coaxial cable Coaxial Cable, with microstrip line Microstrip Line or belt line Strip Line) regard as tube, and the pressure that the location that grasp a canal brings to bear on, be just like the “ on board face to accept end ” (Receiver) component place paralell connection arrives the resistor of Gnd is general, usable in order to adjust its terminal characteristic impedance (Characteristic Impedance) , make match the demand that accepts upright component interior.

 

3, the terminal of transmission line accuses to provide a technology (Termination)

 

3.1, by be duped “ signal ” gallops in transmission line travel and arrive at terminus, be about to enter accept component (the IC that differs like the size such as CPU or Meomery) in when the job, criterion the ” of “ characteristic impedance that place of this line itself has, must want as in-house as terminal component electron impedance to match ability travel each other, such ability does not send the mission failure is white busy. Say with term even if implement a directive correctly, reduce noise interference, avoid wrong action ” . When once each other fail,matching, surely will a few energy turns round to face towards “ sends end ” rebounds, form reflection noise then (Noise) vexed.

 

3.2, the characteristic impedance when transmission line itself (Z0) be ordered to decide by the architect when be 28ohm, criterion the resistor of the ground connection that terminal accuses to be in charge of (Zt) also must be 28ohm, such ability helps transmission line to Z0 maintain, make whole is able to stabilize the design numerical value in 28 Ohm. Also plant here only of Z0=Zt match case to fall, the transmission ability of signal can provide efficiency most, ” of integrality of its “ signal (Signal Integrity, the special technical terms that is signal character) also talent is first-class.

 

4, characteristic impedance (Characteristic Impedance)

 

4.1, when some signal square wave, in the line of transmission line assembly, with allowing high (High Level) when pressing signal to be advanced ahead, be apart from its closest referenced layer (if receive layer) in, theoretic the travel before surely the negative pressure signal that is come out by induction of place of this electric field is accompanied (be equal to pressing the recursive method Return Path with retrorse signal) , the loop of sex of such will achievable whole (Loop) system. In the travel before ” of this “ signal if fly its time for the moment is brief try to freeze, the instantaneous impedance that can imagine its are come from the place such as layer of line, medium and referenced layer to appear jointly is worth (Instantanious Impedance) , this namely ” of characteristic impedance of so called “ . Hereat ” of this “ characteristic impedance should the line with line is broad (W) , the wire is thick (T) , medium ply (H) as invariable as medium (Dk) bought a concern.

 

4.2, because the “ of high frequency signal is characteristic,impedance matchs undesirable consequence impedance ” (Z0) original term is very long, cause is common all of abbreviation for “ impedance ” . Reader ten million should take care, this and alternating current of low frequency AC (60Hz) its electrical wiring (be not transmission line) in, appears impedance is worth (Z) not identical. Digital system can manage appropriate when the Z0 of whole transmission line, and control is inside some limits (±10 ﹪ or ±5 ﹪ ) person, the transmission line with this good quality, will can make noise decreases, and misoperation also can avoid. But 4 kinds of variable when the Z0 in afore-mentioned microstrip lines (W, T, H, R) have either happen unusual, for example when line occurrence separation, will make original Z0 abrupt rise (the fact that the Z0 in seeing afore-mentioned formula and W become inverse ratio) , and cannot continue to maintain due stability even (Continuous) when, criterion the energy of its signal can produce partial advancement necessarily, and the part rebounds however catoptric is short of break. Will not avoid noise and misoperation so. The tube that irrigates a flower for example is stepped on suddenly, cause hose two end appear unusual, as it happens is accountable afore-mentioned characteristic impedance match bad problem.

 

4.3, impedance matchs undesirable cause noise of afore-mentioned partial signal energy rebound, the square wave signal that creates good before character, appear to be out of shape unusually instantly (happen to allow high namely up Overshoot, with low allow an Undershoot that be down, and the Ringing of both follow-up) . Misoperation still can be caused when the high frequency noise such as this is serious, and pulse rate heals at that time fast when noise also makes mistake easily more more more.

 

5, long term transmission impedance matchs a design

 

To high frequency signal, if the arteries and veins of clock pulse signal is wide enough long, so the reflection energy that appears on signal of this clock pulse and ringing energy, will become two by a original more perhaps, the clock pulse signal that causes a system consequently appears unusual. In addition, reflection still can make the noise tolerance of logistic parts of an apparatus becomes poor. In this system design, because radar outputs signal to be 1 KΩ impedance, go against consequently long term transmit, produce signal to reflex a phenomenon. Reflection result forms standing wave to signal of simulative sine wave, digital signal is behaved to rise the edge is mixed drop the ringing of the edge and too strong. Should rush to be able to form intense electromagnetism interference not only too, also can damage use after class the protective diode of input, even invalidation. Graph 1 show a signal to develop weaveform too. Generally speaking, too strong exceed O. 7 V should take corresponding step, in the graph 2 in, signal source impedance, laden impedance is to cause signal catoptric main reason. Because this wants, impedance commutation is 50Ω . With benefit at long term transmit. Chart of basis history close husband is knowable, capacitance or inductance and load establish ties, can increase or reduce laden impedance, and the dot that go up meets its chart ambulate along the circle that represents real resistance. If capacitance or inductance ground connection, criterion the dot on chart is met center of to in an attempt to rotates 180° . Just ambulate along resistance group next, rotate along the center again 180° . Till resistance turns into,repeat afore-mentioned methods 1, can turn into impedance force directly 0, finish so match.

 

 

5.1, systematic work principle

 

In systematic design, keep apart radar to output signal with transformer above all, follow through cent pressing next enlarge, make capacitance is kept apart, output 6 frequency to pile up finally. Graph 3 with the graph 4 give out respectively overall design block diagram and specific circuit design the system.

 

 

5.2, basis of choice of parts of an apparatus and match computation

 

The choice of A, transformer

 

Segregation transformer chooses 1: The transformer of 1. As a result of sub do not be linked together with the ground, because this is sub,assume office there is voltage between a line and ground. The characteristic of segregation transformer is primary with sub separate, make return does not produce between them, but 1: The segregation transformer of 1 is forbidden and sub ground connection. Its principle is shown 5 times like the graph.

 

 

If the v/LIT all over the ground number of sub winding and primary winding is different, criterion the size of E1 of inductive electromotive force and E2 is not same also. Should skip inside after impedance pressing falls, the measurement of voltage U1 and U2 is different also. When sub sky carries transformer, primary had flowed only advocate the voltaic In of magnetic flux, this electric current says for magnetizing current. When sub increase load, when shedding I2 of overload electric current namely, core lieutenant general produces magnetic flux, change with strive advocate magnetic flux, but when primary tension is constant, advocate magnetic flux is changeless also. Right now, primary be about to had shed two parts electric current, one part is magnetizing current I0, one part is I2 of balance electric current, so this part electric current will follow the change of I2 and change. Electric current is multiplied in order to circle number is magnetism situation. Its balance action is action of magnetism power balance essentially, transformer balanced action to come true through magnetism situation namely sub energy is delivered first. Because transformer does not consume power, and the noise of generation is negligible not plan, signal frequency is very so tall, and the input of converter of A ／ D is carried not the add noise with very big be patient of. Accordingly, choice T1—6T transformer will keep apart and converter of D of ／ of A of the class after drive.

 

The choice of converter of B, A/D

 

When choosing converter of A ／ D, basically consider its drive circuit function and follow enlarge function. For this, simplify according to what needing rate of power supply voltage, bandwidth and circuit principle, preliminary choose converter of D of AD8051 A ／ . Use voltage feedback circuit, want to make output amplitude and input amplitude changeless, can lose feedback according to voltage: Auf=U0/UI=1+9RF/R, because this passes converter of A ／ D,magnify its 2 times, but A138051 rate relatively the rate of AD818 is low, weaveform also has certain delay. Graph the 6 comparison that show an output voltage U1 that uses AD8051 parts of an apparatus and the output voltage U2 that use AD818 parts of an apparatus. Be in when frequency high frequency paragraph when lifting ceaselessly, characteristic impedance can be bordering on fixed cost gradually. The principle that the shunt-wound cost that matchs the two resistor in inputting impedance according to the terminal austral Daiwei and photograph of impedance of transmission line character match, the resistor that should match to it in the join of other one aspect of the matter of transmission line, its block is worth the characteristic impedance value that is transmission line. In the design, the impedance of transmission line is 50Ω , match resistor and part of the body after the source carries resistor 50Ω to match to press in transmission terminal so, final output value and former input are identical, but have the delay that makes an appointment with 20ns.

 

C, epilogue

 

Research is long term the key that transmission impedance matchs depends on building match model and computational impedance. Because the computational error of impedance can affect the transmission of signal greatly, below the circumstance that does not match in impedance so, will bring about signal to data is piled up by accident or be passed again. Via experimental test and verify, although of 1 ％ pass again rate, also can increase the error of radar signal pulse, cause data not accurate. Experimental test and verify what what offer is long term transmitting a recipe law is effective, it matchs medium application in impedance to testing systematic technology, and control and the referenced value with analyse diagnostic impedance to have fair.