Electronic device for reducing audio noise caused from unbalanced ground and mobile communication device thereof

1. An electronic apparatus for reducing audio noise caused from unbalanced ground, the electronic apparatus comprising:

a first circuit board comprising:

a first audio source, utilized for providing a first mode audio input; and

a first reference grounding end, utilized as a reference ground of the first circuit board;

a second circuit board comprising:

a second audio source, utilized for providing a second mode audio input; and

a second reference grounding end, utilized as a reference ground of the second circuit board;

a flexible board cable, utilized for coupling the first audio source of the first circuit board to the second circuit board;

a grounding wiring, utilized for coupling the first reference grounding end of the first circuit board to the second circuit board;

a selection unit, disposed on the second circuit board, having a first input end, a second input end, a third input end, a fourth input end, a first output end, and a second output end, wherein the first input end, the second input end, the third input end, and the fourth input end are respectively utilized for receiving the first audio source, the second audio source, the first reference grounding end, and the second reference grounding end, the selection unit selects one from the first audio source and the second audio source to output and selects one from the first reference grounding end and the second reference grounding end to output; and

a receiver, disposed on the second circuit board, having an input end coupled to the first output end of the selection unit and controlled by the selection unit to be coupled to the first audio source or to the second audio source, and a grounding end coupled to the second output end of the selection unit and controlled by the selection unit to be coupled to the first reference grounding end or to the second reference grounding end;

wherein when the first mode audio input is inputted, the selection unit selects to output the first audio source to the first output end and to be coupled to the input end of the receiver, and the selection unit selects to output the first reference grounding end to the second output end and to be coupled to the grounding end of the receiver;

wherein when the second mode audio input is inputted, the selection unit selects to output the second audio source to the first output end and to be coupled to the input end of the receiver, and the selection unit selects to output the second reference grounding end to the second output end and to be coupled to the grounding end of the receiver.

2. The electronic apparatus of claim 1 , wherein the electronic apparatus is a multimode mobile phone.

3. The electronic apparatus of claim 1 further comprising:

a third audio source, disposed on the second circuit board, for providing a third mode audio input.

4. The electronic apparatus of claim 3 , wherein the first mode, the second mode, and the third mode are each a global system for mobile communication (GSM), a personal handy-phone system (PHS), a code division multiple access (CDMA) system, a wideband CDMA system, or a wireless fidelity (Wi-Fi) system.

5. The electronic apparatus of claim 3 , wherein:

the selection unit further comprises a fifth input end utilized for receiving the third audio source, the selection unit selects one from the first audio source, the second audio source, and the third audio source to output to the first output end and selects one from the first grounding end and the second grounding end to output to the second output end; and

the input end of the receiver is coupled to the first output end of the selection unit and is controlled by the selection unit to be coupled to the first audio source, to the second audio source, or to the third audio source, and the grounding end of the receiver is coupled to the second output end of the selection unit and is controlled by the selection unit to be coupled to the first reference grounding end or to the second reference grounding end.

6. The electronic apparatus of claim 5 , wherein:

when the first mode audio input is inputted, the selection unit selects to output the first audio source to the first output end and to be coupled to the input end of the receiver, and the selection unit selects to output the first reference grounding end to the second output end and to be coupled to the grounding end of the receiver;

when the second mode audio input is inputted, the selection unit selects to output the second audio source to the first output end and to be coupled to the input end of the receiver, and the selection unit selects to output the second reference grounding end to the second output end and to be coupled to the grounding end of the receiver; and

when the third mode audio input is inputted, the selection unit selects to output the third audio source to the first output end and to be coupled to the input end of the receiver, and the selection unit selects to output the second reference grounding end to the second output end and to be coupled to the grounding end of the receiver.

7. The electronic apparatus of claim 1 further comprising:

a fourth audio source, disposed on the first circuit board, for providing a fourth mode audio input.

8. The electronic apparatus of claim 7 , wherein the first mode, the second mode, and the fourth mode are each a GSM system, a PHS system, a CDMA system, a wideband CDMA system, or a Wi-Fi system.

9. The electronic apparatus of claim 7 , wherein:

the flexible board cable is further utilized for coupling the fourth audio source of the first circuit board to the second circuit board;

the selection unit further comprises a sixth input end four receiving the fourth audio source, the selection unit selects one from the first audio source, the second audio source, and the fourth audio source to output to the first output end and selects one from the first reference grounding end and the second reference grounding end to output to the second output end; and

the input end of the receiver is coupled to the first output end of the selection unit and is controlled by the selection unit to be coupled to the first audio source, to the second audio source, or to the fourth audio source, and a grounding end of the receiver is coupled to the second output end of the selection unit and is controlled by the selection unit to be coupled to the first reference grounding end or to the second reference grounding end.

10. The electronic apparatus of claim 9 , wherein:

when the first mode audio input is inputted, the selection unit selects to output the first audio source to the first output end and to be coupled to the input end of the receiver, and the selection unit selects to output the first reference grounding end to the second output end and to be coupled to the grounding end of the receiver;

when the second mode audio input is inputted, the selection unit selects to output the second audio source to the first output end and to be coupled to the input end of the receiver, and the selection unit selects to output the second reference grounding end to the second output end and to be coupled to the grounding end of the receiver; and

when the fourth mode audio input is inputted, the selection unit selects to output the fourth audio source to the first output end and to be coupled to the input end of the receiver, and the selection unit selects to output the first reference grounding end to the second output end and to be coupled to the grounding end of the receiver.

11. The electronic apparatus of claim 1 , wherein the grounding wiring directly couples the first reference grounding end of the first circuit board to the second circuit board through a welding.

12. The electronic apparatus of claim 1 , wherein the selection unit comprises at least one switch or a multiplexer.

13. The electronic apparatus of claim 1 , wherein the receiver is a single-end audio input device.