PCB ground wire design_ Single point grounding_ Bobbin line bold

There are four main ways of grounding ： Single point ground 、 Multi point grounding 、 Floating and hybrid grounding .

Single point ground ： As shown in the figure on the right , Only one physical point of the system is defined as the grounding reference point , All parts of the circuit that need to be grounded are connected to this point . Single point ground is suitable for low frequency circuits , Generally, the frequency is less than 1MHz, The main reason is that the low-frequency circuit is not sensitive to ground impedance . Digital and analog 、DC-DC Power ground and signal ground are usually single point grounded , This single point grounded physical point is multi-purpose 0 Ohmic resistor or bead connected to main ground .

Multi point grounding ： After the system becomes more frequent , commonly 10MHz above , Multi point grounding is recommended . As shown on the left above , Multipoint grounding is to connect each grounding point directly to the nearest grounding plane .

１. Single point ground

There are two types of single point grounding ： One is series single point grounding , The other is parallel single point grounding .

** In series single point grounding , There is a common impedance between many circuits , Therefore, the mutual interference caused by common impedance coupling is very serious .

Interference of series single point grounding ：
A The potential at point is ：VA = ( I1 + I2 + I3 ) R1
A The potential at point is ：VB = ( I1 + I2 + I3 ) R1 + ( I2 + I3 ) R2
C The potential at point is ： VC = ( I1 + I2 + I3 ) R1 + ( I2 + I3 ) R2 + I3 R3
It can be seen from the formula that ,A、B、C The potential at each point is affected by the working current of the circuit , Varies with the ground current of each circuit . In especial C Point potential , Very unstable .

Although this grounding method has great problems , Is actually the most common , Because it's very simple . But in the hybrid system of high-power and low-power circuits , Never use , Because the ground current in the high-power circuit will affect the normal operation of the low-power circuit . in addition , The most sensitive circuit should be placed in A spot , This potential is the most stable . in addition , From the amplifier discussed above, we know , The power output stage should be placed in A spot , The preamplifier is placed in B、C spot .

The solution to this problem yes

Parallel single point grounding

however , More conductors are required for parallel single point grounding , Series connection can be adopted in practice 、 Parallel hybrid grounding .