Ground wire also has impedance, when electric current has shed ground wire, can produce tension, this is noise voltage, and one of interference sources that noise voltage is influence system stability, not desirable. So, wanting the premise that reduces ground wire noise is the impedance that reduces ground wire.

 

Well-known, ground wire is the access that electric current returns a source. As the wide application of circuit of large scale integration and high frequency circuit, the ground wire design of low impedance appears in circuit particularly important. Here lists a few kinds of commonly used ground connection methods simply:

 

Sheet nods ground connection

 

Sheet nods ground connection, just as its name implies, receive all return in circuit namely onefold, on same referenced potential point. Following plan institute are shown.

 

 

Spot ground contact can divide sheet to establish ties for “ ground connection ” and ” of ground connection of “ paralell connection two kinds of means. The way that series connection sheet chooses ground connection is simple, but the account that is put in collective ground wire, cause presence impedance of communal ground wire, if establish ties right now,those who be together is power differs very big circuit, so mutual interference is very serious. Shunt-wound sheet nods the means of ground connection to be able to prevent the ingredient of coupling of communal ground wire, but every part circuit needs to make ground wire to ground connection dot, the ground wire of need is overmuch, not practical.

 

So, when applying actually, can use series connection and shunt-wound compound means of only place ground contact. When drawing PCB board, put the circuit that disturbs not easily each other, the circuit mutual incidental interference puts different layer, accept the ground parallel connection of different layer again the ground. Following plan institute are shown.

 

 

Only place ground contact is inside high frequency circuit, because ground wire is long, the impedance of ground wire is the ingredient that cannot prevent forever, so not applicable, how does that do? ” of ground contact of “ much spot introduces again below.

 

Many bits of ground connection

 

Work when circuit when frequency is taller, imagine high frequency signal is when transmission of edge touchdown line, the point that reachs affects circumjacent circuit to be able to have how serious, accordingly all circuit are about nearby receives the ground to go up, ground wire requirement is the shortest, many bits of ground connection arose.

 

Many bits of ground connection, its purpose is to reduce the impedance of ground wire, be in high frequency (below the condition with certain F) in circuit, want to reduce impedance, basically consider from two respects, it is to reduce ground wire resistance, 2 it is to reduce ground wire inductance.

 

1, reduce resistance of ground wire conductor, from inside the relation formula of resistor and cross section we know, want to increase ground wire to guide the cross section that connect is accumulated. But in high frequency environment, the hasten skin effect that is put in a kind of high frequency electric current (also call collect skin effect) , high frequency electric current can be passed in conductor surface, so pure the cross section that increases ground wire conductor is accumulated often effect is not big. Can consider to be in conductor surface is silver-gilt, because silver-colored conductivity is otherer electric material is outstanding, can reduce conductor resistance so.

 

2, reduce the inductance of ground wire, best method increases the acreage of ground wire namely.

 

When applying actually, ground wire is short, ground area is large, it is better that the effect of interference rejection is met.

 

When writing here, somebody can ask the likelihood, how be just high frequency circuit? The literature that referenced Yang Jishen teachs " electromagnetism is compatible EMC technology " have mention “ low frequency circuit calculates under 1MHZ normally, can use sheet to nod ground connection, 10MHZ above calculates high frequency circuit, can use the means ” of many bits of ground connection, when 1MHZ and 10MHZ, if the longest ground wire does not exceed the 1/20 of wavelengh, can only place ground contact, otherwise many bits of ground connection.

 

If there is high frequency signal already in circuit, have low frequency signal again, how to do? Mixture ground connection can be a good choice!

 

Mixture ground connection

 

If plan institute is shown.

 

 

Will analyse through the graph.

 

The first kind of structure in pursueing on, assume the job is in low frequency circuit, according to capacitive reactance Zc = 1/2πfc knowable, capacitive reactance is very big below low frequency environment, and below high frequency environment very small. So ground wire is disconnecting when low frequency, in be close to when high frequency interference guide. Receive a standard so the disturbing influence of road of annulus of ground wire of OK and significant avoidance.

 

The 2nd kind of structure in pursueing on, assume the job is in high frequency circuit, according to inductance Zl = 2πfl knowable, inductance is very small below low frequency environment, and below high frequency environment very big. So ground wire is similar when low frequency guide connect, be in getting is to disconnect when high frequency interference. Receive a standard so the influence of electric current of road of annulus of ground of OK and significant avoidance.

 

Overview, in applying actually, it is OK that circuit uses appropriate ground connection means according to working environment significant avoidance disturbs signal, achieve the best result of circuit.