For PCB layout engineers, today's mobile phone presents the ultimate challenge. Modern mobile phones include almost all sub-systems that can be found in portable devices, such as a variety of radio frequency modules (including cellular, short-range wireless transmission); audio, video subsystems; dedicated application processors, More and more applications to increase the I / O layout, and each subsystem has conflicting requirements.

In such a small space to integrate so many complex subsystems, the reality to be considered is also all-encompassing, in addition to the same interference between the RF subsystem, the various subsystems may be self-operation or by the wiring Of mutual interference, EMI problems, etc., are testing the professional capacity of mobile phone PCB engineers.

A well-designed circuit board must be able to maximize the performance of each component mounted on it and avoid interference between different systems. Because if the conflict between the subsystems of the situation, the result will inevitably lead to performance degradation.

Today, despite the increasing functionality of audio in mobile phones, much attention has been focused on radio frequency subsystems in circuit board designs, where audio circuits are often least concerned. However, the audio quality, especially with high-quality sound characteristics, has become a high-end mobile phone can quickly accept one of the key points for the market. This article provides some suggestions to help ensure that a circuit board with good layout without sacrificing audio quality is achieved.

1 recommended practice

* Consider the layout plan carefully. Ideal layout planning Different types of circuits should be divided into different areas to minimize interference.

* Use differential signals whenever possible. An audio component with a differential input can suppress noise.

* Isolate the ground current to avoid the digital current to increase the noise of the analog circuit.

* Analog circuit using star ground. The current consumption of the audio power amplifier is usually very large, which may have an adverse effect on their own ground or other reference ground.

* Turn unused area on the board into a ground plane. A ground flood is performed near the signal trace, and unwanted high frequency energy in the signal line can be connected to the ground via capacitive coupling.

2 not recommended practice

* Use a hybrid circuit on the board. Although the radio frequency area of ​​the handset is generally considered to be analog, the noise from the RF band coupled to the audio circuit may be demodulated into audible noise.

* The analog audio signal on the board is too long. Too long analog audio stitches may absorb noise from digital and RF circuits.

* Forget the importance of grounding loops. Poorly grounded systems are likely to experience severe distortion, noise, crosstalk, and low RF immunity.

* Interrupt the digital current of the natural circuit. The path of the path of the smallest, the antenna and the impact of the sensor can be reduced to a minimum.

The handset circuit board design affects audio performance
Figure (text): * In the layout of the mobile phone circuit board, you should carefully consider the layout plan, the ideal situation is to different types of circuits in different areas to avoid interference.