Coupling and retreat Ou

 

What is coupling capacitance? What is to go Ou circuit?

 

Coupling points to the process that signal transfers to the 2nd class by the first class, when making clear, be not being added commonly often is to point to communication coupling.

 

Retreating Ou is to point to pair of power source to take further filter wave step, the signal between two class passes purify the influence that power source disturbs each other. Coupling constant is to show coupling capacitance value and impedance of input of the 2nd class are worth the time constant of product correspondence.

 

Retreat Ou to have 3 objectives:

 

The purify of high frequency ripple in 1. general power source, the access that strings together the high frequency signal of multistage amplifier faze each other through power source is cut off.

 

When 2. big signal works, circuit is increased to power source demand, cause power source wave motion, through removing the power source when Ou drops big signal wave motion is opposite input class / the influence of level of tall voltage gain;

 

3. forms suspension ground or be suspension power source, the noise of coordinates an active parts of an apparatus to arise when switch high frequency switch that each part ground wire is finished in complex system or is power source will travel along power supply cord. Go the main function of Ou capacitance offers a local direct current source to give active parts of an apparatus namely, be in in order to reduce switch noise board the transmission that go up and reach noise guiding the ground.

 

Quote from Lun Dequan ” the electromagnetism of circuit board class is compatible design ” one article, this paper is mixed to noise Ou method, go the use of Ou capacitance and bypass capacitance is told well. Consult please.

 

The coupling means of interference

 

The interference signal that disturbs source generation is to pass particular coupling channel to be opposite electronic-controlled systematic happening electromagnetism disturbs action. The coupling means no more than of interference is to pass the action such as lead, space, common thread to be in electronic-controlled on the system.

 

The analysis comes down to basically have the following kinds.

 

Direct coupling: This is interference invades the directest way, also be a kind of pattern with the most general existence in the system. If disturb signal,build the interference of didymous system through lead. To means of this kind of coupling, can use filter wave to go to what the method of Ou restrains electromagnetism effectively to disturb signal passing into.

 

Communal impedance coupling: This also is pattern of familiar a kind of coupling. The electricity that often produces in two circuit has the case of collective access. Communal impedance coupling has common ground and power source impedance two kinds. Prevent this kind of coupling to should make faze source mixes Yu Ling of coupling impedance approach, desiccate to be disturbed there is communal impedance between the object.

 

Capacitance coupling: Call electric field coupling or electrostatic coupling again, it is the means of a kind of coupling of as a result of the existence of distributinging capacitance generation.

 

Electromagnetism induction coupling: Call magnetic field coupling again. It is the means of a kind of coupling as a result of induction of interior or magnetic field of outer space report, the commonly used method that prevents this kind of coupling is the parts of an apparatus to sufferring interference easily or circuit try screen.

 

Radiation coupling: The radiate of electromagnetism field also can cause interference coupling, it is interference of a kind of ruleless. This kind of interference is passed very easily in the system through power supply cord. Become additionally when signal transmission line is longer, they can radiation interference wave and receive interference wave, call spread cables effect.

 

Coupling of leakage of electricity: Coupling of alleged leakage of electricity is resistor sex coupling. This kind of interference often happens when insulation is reduced. Remember previously my viewpoint is: Go lotus root capacitance is general the size is larger, avoid noise coupling to arrive namely the meaning of other part; Bypass capacitance size is small, offer the noise circumfluence way of low impedance. Actually this kind of view also can calculate without what big mistake. But the course consulted occasionally relevant data, just discover actually Decouple is mixed Bypass from come up at all say to do not have any distinction, both OK on appellation crossing-over. Both action low common said: Use when power source.

 

Alleged noise is the wave motion of power source actually, power source wave motion comes from at two respects: The wave motion of power source itself, the tension that load changes to voltaic demand and the difference of corresponding ability brings power source system is fluctuant. And go lotus root and bypass capacitance are the noise that causes relative to laden change for. So they were not necessary twice to do divisional. And the size that actually capacitance is worth, the amount also is rational talking basis but of abide, if choose at will, may encounter below certain circumstance go lotus root capacitance (bypass) the situation that produces self-oscillation with distributinging parameter. So on real significance go lotus root and bypass are a basis for the actual condition of load and power supply system. Not was necessary to do divisional, also do not have substaintial distinction.

 

Capacitance is the cell that uses surely in board card design, the stand or fall of its character has become us to judge a of board card quality very important facet.

 

The function of ① capacitance and represent a means.

 

By two metallic pole, intermediate clip has insulation medium to form. The character of capacitance basically is to lie between straight current communicating, because this is multi-purpose at wave of the coupling between class, filter, go Ou, bypass and signature humorous. Capacitance adds a number to express with “C” in circuit, for instance C8, state in circuit number is the capacitance of 8.

 

The classification of ② capacitance.

 

Capacitance differs by medium cent is: Aeriform medium capacitance, liquid medium capacitance, capacitance of inorganic solid medium, capacitance of organic solid medium electroanalysises capacitance. By polarity cent is: Have polarity capacitance and without polarity capacitance. Can divide by the structure for: Secure capacitance, alterable capacitance, fine tuning capacitance.

 

The capacity of ③ capacitance.

 

Capacitance size indicates can the size of electric energy of keep in storage. Capacitance calls capacitive reactance to communicating the block up action of signal, capacitive reactance and the frequency that communicate signal and capacitance are concerned, capacitive reactance XC=1/2πf C (f expresses to communicate the frequency of signal, c expresses capacitance capacity) .

 

The unit of capacity of ④ capacitance and compression.

 

The main unit of capacitance is F (law) , other unit still has: Millifarad (MF) , small way (UF) , accept law (NF) , leather law (PF) . Because the size of unit F is too large, the is μF, NF, PF commonly unit that so we see. Conversion concerns: 1F ＝ 1000000μF, 1μF=1000nF=1000000pF.

 

Each capacitance has its compression value, express with V. Do not have commonly extremely of capacitance nominal compression cost has higher: 63V, 100V, 160V, 250V, 400V, 600V, 1000V. Have extremely the compression photograph of capacitance is comparative and inferior, general and nominal compression value has: 4V, 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 220V, 400V.

 

The tagging of ⑤ capacitance method and capacity error.

 

The tagging of capacitance methodological cent is: Straight mark law, color patch law and several mark law. Compare large electric capacity to bulk, use straight mark method more. If be 0.005, express 0.005uF=5nF. If be 5n, that is denotive it is 5nF.

 

Figure mark way: Represent capacity bulk with 3 digit word commonly, before two represent significance word, word of the 3rd digit is of 10 how many times square. Be like: 102 express 10x10x10 PF=1000PF, 203 express 20x10x10x10 PF. Law of Nn color patch, along capacitance down-lead direction, show different number with different color, the first, 2 kinds of annulus express capacitance, an of 0 number after the 3rd kind of color represents significance word (the unit is PF) . The numerical value that color represents is: =3 of =1 of black =0, palm, red =2, orange, yellow =4, green =5, blue =6, violet =7, grey =8, white =9.

 

Capacitance capacity error expresses with symbolic F, G, J, K, L, M, allow an error to part correspondence is ±1% , ±2% , ±5% , ±10% , ±15% , ±20% .

 

Negative pole distinguishs and measuring of ⑥ capacitance.

 

What there is a sign above capacitance is black piece for negative pole. On PCB capacitance has two semicircle locally, coloreded semicircle brings a foot correspondingly to be negative pole. The useful also accident that cite a base will distinguish negative pole long foot is, short foot is negative.

 

Do not know electric capacity when us when negative pole, can be measured with avometer. Capacitance is polar the medium between is not absolutely dielectric, its resistor also is not infinity, however a finite numerical value, be in 1000 million Europe commonly above. Capacitance is polar the resistor between is called insulation resistance or resistor of leakage of electricity. Electroanalysis only the anode of capacitance receives power source (the black list pen when resistor is blocked) , negative termination power source is lost (the red watch pen when resistor is blocked) when, electroanalysis the leakage current of capacitance gift is little (block of leakage of electricity is large) . Conversely, electroanalysis the leakage current of capacitance increases (block of leakage of electricity is reduced) . Such, we assume first some very “+” extremely, avometer chooses R*100 or R*1K is blocked, the “+” that will assume next extremely with the black list of avometer the pen connects, the red watch pen of another electrode and avometer is conterminous, write down scale of next the inactive that express a needle (watch needle relies on left block the value is great) , can numerate directly to digital avometer reading. Discharge capacitance next (two down-lead are touched) , next two exchange that express a pen, undertake metrical afresh. In be being measured twice, the position that watch needle keeps finally leans left (or block value is great) that, what black list pen receives is to electroanalysis the anode of capacitance. A few experience that Nn ⑦ capacitance uses and come 4 errors.

 

A few experience: When the polarity that cannot fix line in circuit, the proposal is used without extremely electroanalysis capacitance. Through electroanalysising the ripple electric current of capacitance cannot exceed its admissibility range. If exceeded formulary value, need to choose be able to bear or endure the capacitance of big ripple electric current. The working voltage of capacitance cannot exceed his rated voltage. Solder in what have electric capacity when, electric iron should maintain certain distance with the plastic outer covering of capacitance, cause plastic bushing rupture in order to prevent overheat. And weld time should not exceed 10 seconds, solder temperature should not exceed 260 Celsius.

 

4 errors:

 

● capacitance capacity has been jumped over greatly more.

 

A lot of people are in the in replacing, often loves to use high capacity capacitance of capacitance. Although electric capacity is larger,we know, the voltaic compensatory capability that provides for IC is stronger. And the volume that the accretion that does not say capacitance size brings greatens, raise cost while influence air flows and still come loose hot. The key depends on inductance of parasitism of the existence on capacitance, discharge loop meets capacitance produce resonance on dot of a certain frequency. In syntonic dot, the impedance of capacitance is small. The impedance of discharge loop is the accordingly smallest, the effect of complementary capabilities is best also. But when frequency exceeds syntonic drop, the impedance of discharge loop begins to increase, capacitance offers voltaic ability to begin to drop. The look value of capacitance is greater, syntonic frequency is lower, the frequency scope that capacitance can compensate electric current effectively is less also. For the angle from the ability that makes sure capacitance provides high frequency electricity, the viewpoint that capacitance has jumped over greatly more is wrong, general circuit has a referenced value in the design.

 

The capacitance of ● same size, paralell connection jumps over much small electric capacity to had been jumped over, compression value, be able to bear or endure equivalent resistor of lukewarm value, look value, ESR() a few etc is capacitance important parameter, natural to ESR it is lower better.

 

The capacity of ESR and capacitance, frequency, voltage, temperature relative. Secure moment when voltage, the size is larger, ESR is lower. In board card plan in use many small electric capacity and be being connected is a limitation with PCB space more, such some people think, jump over much shunt-wound little resistance, ESR is lower, the effect is better. Theoretic it is such, but the impedance that should receive crural solder to nod considering capacitance, use parallel connection of many small electric capacity, the effect is not certain and outstanding.

 

● ESR is lower, the effect is better.

 

Join the rise power supply circuit above us for, to input capacitance, the capacity that inputs capacitance wants a bit bigger. Relative to the requirement of the capacity, the requirement to ESR can be reduced appropriately. Because input capacitance basically is compression, it is the switch pulse that absorbs MOSFET next. To output electric capacity, the requirement of compression and capacity can be reduced appropriately a bit. The demand of ESR is a bit higher, what because here wants,assure is enough electricity current excess. But what here should notice is ESR not be lower better, low ESR capacitance can cause switch circuit oscillation. And disappear brace up circuit is complex the addition that can cause cost at the same time. In board card design, here has a referenced value commonly, this chooses parameter as component, avoid need brace up circuit and the addition that causes cost.

 

● good capacitance is being represented high quality.

 

 “ only capacitance talks ” once be in fashion for a period, a this thing make it with a few manufacturers and sedulous also media sell a site. In board card design, circuit design level is crucial. Can make with two-phase power supply with some manufacturers like introducing the product with 4 bearings steadier power supply than a few manufacturers, blindly use costly electric capacity, can not make good product certainly. Measure a product, must all-around of much angle go considering, must not the action capacitance is intended innocently exaggerated.

 

Pull on with next pulling

 

Resistance helps on:

 

1, when circuit of COMS of TTL circuit drive, if the tall n of TTL circuit output the lowermost tall n under COMS circuit (it is 3.5V commonly) , need to help resistance on the output termination of TTL at this moment, in order to raise the cost of output tall n.

 

2, OC door circuit must be added help resistance, ability is used.

 

3, the drive ability that cites a base to increase output, some sheet piece often also use on machine pin on help resistance.

 

4, go up in COMS chip, to prevent electrostatic cause damage, unused pin cannot impending, receive commonly on pull resistor generation to reduce input impedance, provide access of discharge carry on one’s shoulder.

 

5, the pin of chip is added pull resistor to raise output n, the noise allowance that increases chip to input signal thereby enhances interference rejection ability.

 

6, those who increase bus line fight electromagnetism to disturb ability. The electromagnetism of impending more recipient outside disturbs pin.

 

7, long term the resistor in transmitting does not match to cause reflection wave interference easily, adding fluctuation to help resistance is resistor match, effective inhibition reflexes an interference.

 

The choice principle that resistor block value drags on includes:

 

1, consider from the ability of fill electric current of managing power comsumption and chip ought to enough big; Resistance is great, electric current is small.

 

2, from ensure enough drive electricity considers ought to enough small; Resistance is little, electric current is big.

 

3, to high speed circuit, pass to go up greatly help resistance likelihood edge flatten delay. Integrated consideration

 

Above at 3 o’clock, arrive in 1k normally between 10k choose. To next pulling resistor also has similar reason

 

Pull resistor and the input character that play the choice that helps resistance to should combine switch to be in charge of character and inferior circuit to have set to going up, main need considers the following factors:

 

1. The balance of drive ability and power comsumption. Above pulls resistor to be exemple, popularly says, resistance is helped on smaller, drive capability is stronger, but power comsumption is bigger, the design is to should notice both between balanced.

 

2. The drive demand of inferior circuit. Same above pulls resistor to be exemple, when outputting tall n, switch canal disconnects, resistor is pulled to should choose to provide enough electricity with can be down class circuit appropriately on.

 

3. The set of n of on any account. The doorsill n of the n of on any account of different circuit can have different, resistor should appropriate set can output correct n with ensuring. Above pulls resistor to be exemple, when outputting low n, switch canal guides, resistor and switch canal are pulled to guide electrify block cent presses a value to should ensure on it is under 0 n doorsill.

 

4. Frequency character. Above pulls resistor to be exemple, the input capacitance between the capacitance between resistor and course of cause of switch canal leakage and inferior circuit is pulled to be able to form RC defer on, resistance is greater, defer is bigger. The circuit of Lv of set take an examination that resistance helps on is in the demand of this respect.

 

The principle of the set that resistor plays below and go up helping resistance is same.

 

Condition of a tall block is when OC door outputs tall n, electric current is pulled to want on its by on pull resistor to offer, set an input to carry every port to not be more than 100uA, set electric current of output mouth drive to make an appointment with 500uA, standard job voltage is 5V, the door of n of on any account that inputs a mouth is restricted to be 0.8V(to be low n) under this value; Door of 2V(tall n is restricted to be worth) .

 

Choose on when helping resistance:

 

500uA X 8.4K= 4.2 chooses end of the output when be more than 8.4K to be able to fall namely pull to 0.8V the following, this is value of the smallest block, again small pull no less than coming. If electric current of output mouth drive is bigger, criterion block value can be reduced, when assuring next pulling can under 0.8V can.

 

When outputting tall n, the leakage current of oversight pipe, two inputs mouth needs 200uA

 

200uA X15K=3V go up namely pull resistor pressing to fall for 3V, output mouth can achieve 2V, this block value is value of the largest block, do not pull 2V greatly again. Choose 10K to be able to be used. Of COMS door can consult 74HC series

 

The leakage current of the pipe when the design cannot oversight, electric current of border of IO a cause for gossip also is different below different n, afore-mentioned it is a principle merely, a word is wraparound for: When outputting tall n, should feed full the input mouth from the back, output low n does not feed output mouth maintained (otherwise the input mouth that redundant electric current fed cascade, door of prep above low n is restricted to be worth fluky)