Modern mobile phones contain almost all subsystems found in portable devices, such as various radio frequency modules (including cellular, short-range wireless transmission); audio and video subsystems; dedicated application processors, and The I/O layout increases as more and more applications demand, and each subsystem has conflicting requirements.
To integrate so many complex subsystems in such a small space, the reality to be considered is also all-encompassing. In addition to the possible interference between the same RF subsystems, the different subsystems may operate by themselves or be caused by wiring. The mutual interference, EMI problems, etc., all test the professional ability of mobile phone PCB engineers.
A well-designed board must maximize the performance of every component mounted on it and avoid interference between different systems. Because if there is a conflict between the subsystems, the result will inevitably lead to performance degradation.
Today, despite the ever-increasing audio functionality in mobile phones, much attention remains on the RF subsystem in circuit board design, with audio circuits often receiving the least attention. However, audio quality, especially with high-fidelity sound quality, has become one of the key points affecting the rapid market acceptance of a high-end mobile phone. This article provides some suggestions to help ensure a well laid out board without sacrificing audio quality.
Recommended practice
*Carefully consider layout planning. An ideal floorplan should divide the different types of circuits into different areas to minimize interference. The picture above shows a good layout plan.
*Use differential signals whenever possible. Audio components with differential inputs can suppress noise.
*Isolate ground current to prevent digital current from adding noise to analog circuits.
*Analog circuits use star ground. Audio power amplifiers typically draw large amounts of current, which can adversely affect their own ground or other reference grounds.
* Turn all unused areas on the board into ground planes. By performing a ground flood near the signal trace, unwanted high frequency energy in the signal line can be capacitively coupled to ground.
Not recommended practice
* Use a hybrid circuit on the board. Although the RF region of a cell phone is generally considered analog, noise coupled into the audio circuit from the RF region can be demodulated into audible noise.
*The analog audio signal wiring on the circuit board is too long. Analog audio traces that are too long can absorb noise from digital and RF circuits.
*Forget the importance of ground loops. Poorly grounded systems are likely to suffer from severe distortion, noise, crosstalk, and low RF immunity.
*Break the natural loop of digital current. This path has the smallest loop area and minimizes the effects of antennas and induction.
