PCB and signal transmission system

1. A printed circuit board (PCB), comprising:

a connection module,

at least two signal layers, and

at least two reference layers, wherein:

the at least two signal layers and the at least two reference layers are spaced apart;

the connection module comprises a first connection terminal and a second connection terminal;

the first connection terminal is connected to at least one first signal layer in the at least two signal layers, and is connectable to an external optical interface;

the second connection terminal is connected to at least one second signal layer in the at least two signal layers, and is connectable to an external electrical interface; and

each of the at least two reference layers is provided with a through-hole, and for each of the at least two reference layers, there is an overlapping region between a projection region of an orthogonal projection of the connection module onto the reference layer and a hole region of the through-hole arranged on the reference layer.

2. The PCB according to claim 1 , wherein for each of the at least two reference layers, the overlapping region between the projection region of the orthogonal projection of the connection module onto the reference layer and the hole region of the through-hole arranged on the reference layer meets a condition that:

the projection region of the orthogonal projection of the connection module onto the reference layer partially overlaps with the hole region of the through-hole arranged on the reference layer.

3. The PCB according to claim 1 , wherein for each of the at least two reference layers, the overlapping region between the projection region of the orthogonal projection of the connection module onto the reference layer and the hole region of the through-hole arranged on the reference layer meets a condition that:

the hole region of the through-hole arranged on the reference layer covers the projection region of the orthogonal projection of the connection module onto the reference layer.

4. The PCB according to claim 1 , wherein for each of the at least two reference layers, the overlapping region between the projection region of the orthogonal projection of the connection module onto the reference layer and the hole region of the through-hole arranged on the reference layer meets a condition that:

the projection region of the orthogonal projection of the connection module onto the reference layer exactly overlaps with the hole region of the through-hole arranged on the reference layer.

5. The PCB according to claim 1 , further comprising a power source layer, wherein:

the at least one first signal layer and a first reference layer in the at least two reference layers are located at a first side of the power source layer, wherein the first reference layer corresponds to the at least one first signal layer; and

the at least one second signal layer and a second reference layer in the at least two reference layers are located at a second side of the power source layer, wherein the second reference layer corresponds to the at least one second signal layer.

6. The PCB according to claim 5 , wherein:

the number of the at least one first signal layer is same as the number of the at least one first reference layer, and the at least one first signal layer and the at least one first reference layer are alternately arranged;

the number of the at least one second signal layer is same as the number of the at least one second reference layer, and the at least one second signal layer and the at least one second reference layer are alternately arranged; and

at each of the first side and the second side of the power source layer, one of the at least two reference layers is adjacent to the power source layer.

7. A signal transmission system, comprising:

an expansion interface, and

a printed circuit board PCB, wherein:

the expansion interface comprises one of an optical interface and an electrical interface;

the PCB comprises a connection module, at least two signal layers, and at least two reference layers;

the at least two signal layers and the at least two reference layers are spaced apart;

the connection module comprises a first connection terminal and a second connection terminal;

the first connection terminal is connected to at least one first signal layer in the at least two signal layers, and the first connection terminal is connectable to the optical interface in a case that the expansion interface comprises the optical interface;

the second connection terminal is connected to at least one second signal layer in the at least two signal layers, and the second connection terminal is connectable to the electrical interface in a case that the expansion interface comprises the electrical interface; and

each of the at least two reference layers is provided with a through-hole, and for each of the at least two reference layers, there is an overlapping region between a projection region of an orthogonal projection of the connection module onto the reference layer and a hole region of the through-hole arranged on the reference layer.

8. The signal transmission system according to claim 7 , wherein:

in a case that the expansion interface comprises the optical interface,

a GND-removed region is provided on an outer shell of the optical interface, and the GND-removed region exactly overlaps with the projection region.

9. The signal transmission system according to claim 7 , wherein:

in a case that the expansion interface comprises the electrical interface,

the signal transmission system further comprises a network port transformer, and the network port transformer is connected to the connection module and the electrical interface.

10. The signal transmission system according to claim 7 , wherein:

in a case that the expansion interface comprises the optical interface, the optical interface is connected to the first connection terminal; and

in a case that the expansion interface comprises the electrical interface, the electrical interface is connected to the second connection terminal.

11. The signal transmission system according to claim 7 , wherein for each of the at least two reference layers, the overlapping region between the projection region of the orthogonal projection of the connection module onto the reference layer and the hole region of the through-hole arranged on the reference layer meets a condition that:

the projection region of the orthogonal projection of the connection module onto the reference layer partially overlaps with the hole region of the through-hole arranged on the reference layer.

12. The signal transmission system according to claim 7 , wherein for each of the at least two reference layers, the overlapping region between the projection region of the orthogonal projection of the connection module onto the reference layer and the hole region of the through-hole arranged on the reference layer meets a condition that:

the hole region of the through-hole arranged on the reference layer covers the projection region of the orthogonal projection of the connection module onto the reference layer.

13. The signal transmission system according to claim 7 , wherein for each of the at least two reference layers, the overlapping region between the projection region of the orthogonal projection of the connection module onto the reference layer and the hole region of the through-hole arranged on the reference layer meets a condition that:

the projection region of the orthogonal projection of the connection module onto the reference layer exactly overlaps with the hole region of the through-hole arranged on the reference layer.

14. The signal transmission system according to claim 7 , wherein

the PCB further comprises a power source layer;

the at least one first signal layer and a first reference layer in the at least two reference layers are located at a first side of the power source layer, wherein the first reference layer corresponds to the at least one first signal layer; and

the at least one second signal layer and a second reference layer in the at least two reference layers are located at a second side of the power source layer, wherein the second reference layer corresponds to the at least one second signal layer.

15. The signal transmission system according to claim 14 , wherein:

the number of the at least one first signal layer is same as the number of the at least one first reference layer, and the at least one first signal layer and the at least one first reference layer are alternately arranged;

the number of the at least one second signal layer is same as the number of the at least one second reference layer, and the at least one second signal layer and the at least one second reference layer are alternately arranged; and

at each of the first side and the second side of the power source layer, one of the at least two reference layers is adjacent to the power source layer.