The influence of mobile phone motherboard PCB design on sound quality
For PCB layout engineers, today's mobile phones pose the ultimate challenge. Modern mobile phones include almost all subsystems found in portable devices, such as a variety of RF modules (including cellular and short-range wireless transmission); Audio and video subsystem; Dedicated application processor and I/O layout to meet more and more application requirements, and each subsystem has conflicting requirements.
To integrate so many complex subsystems in such a small space, we should consider all kinds of realities. In addition to the possible interference between RF subsystems, the mutual interference and EMI problems between different subsystems, which may be caused by their own operation or wiring, all test the professional ability 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 there are conflicts between subsystems, the performance will inevitably decline.
Today, despite the increasing audio functionality in mobile phones, much attention is still focused on the RF subsystem in circuit board design, and the audio circuit is often the least concerned. However, audio quality, especially the characteristics of high fax audio quality, has become one of the key points that affect whether a high-end mobile phone can be quickly accepted by the market. This article provides some suggestions to help ensure that a well laid out circuit board is implemented without sacrificing audio quality.
1 Recommended practice
*Carefully consider the layout planning. The ideal layout planning should divide different types of circuits into different areas to minimize interference.
*Use differential signals whenever possible. Audio components with differential inputs can suppress noise.
*Isolate the grounding current to prevent the digital current from increasing the noise of the analog circuit.
*The analog circuit uses star grounding. The current consumption of audio power amplifiers is usually large, which may have a negative effect on their own grounding or other reference grounding.
*Turn all unused areas on the circuit board into ground plane. Perform ground floor near the signal trace, and the unwanted high-frequency energy in the signal line can be coupled to the ground through capacitance.
2. Unsupported practices
*Use hybrid circuits on the circuit board. Although the RF area of mobile phones is generally considered to be analog, the noise coupled to the audio circuit from the RF area may be demodulated into audible noise.
*The analog audio signal wiring on the circuit board is too long. Too long analog audio traces may absorb noise from digital and RF circuits.
*Forget the importance of grounding loop. A poorly grounded system is likely to suffer from serious distortion, noise, crosstalk, and low RF immunity.
*Interrupt the natural circuit of digital current. This path has the smallest loop area, which can minimize the influence of antenna and induction.
PCB manufacturers, PCB designers and PCBA manufacturers will explain the impact of PCB design on the sound quality of mobile phone motherboards.