Electronic Design - Improve mobile phone audio performance PCB design

For PCB layout engineers, mobile phones pose the ultimate challenge. Modern mobile phones contain almost all subsystems found in portable devices, and each subsystem has conflicting requirements. A well-designed circuit board must maximize the performance of each device connected to it and avoid interference between multiple systems. The inconsistent requirements of the various subsystems will inevitably lead to performance degradation.

Although the audio functionality in mobile phones continues to increase, audio circuits often receive the least attention during the circuit board design process. Some suggestions are given below to help ensure a well-layout circuit board without sacrificing audio quality.

should

-Carefully consider the underlying planning. The ideal bottom plan should divide different types of circuits into different areas.

-Use differential signals as much as possible. Audio devices with differential inputs can suppress noise. It is generally not possible to add a ground wire in the middle of the differential signal. Because the most important point of the application principle of differential signals is to use the benefits of mutual coupling between differential signals, such as magnetic flux elimination and noise immunity. If you add a ground wire in the middle, it will destroy the coupling effect. There are two points to pay attention to in the layout of the differential pair. One is that the length of the two wires should be as long as possible, and the other is that the distance between the two wires (the distance is determined by the differential impedance) must be kept constant, that is, to keep parallel. There are two parallel ways, one is that the two wires run on the same side-by-side, and the other is that the two wires run on two adjacent layers above and below (over-under). Generally, the former has more side-by-side implementations.

-Isolate the ground current to avoid the digital current from increasing the noise of the analog circuit. Basically, it is right to divide and isolate the analog/digital ground. It should be noted that the signal trace should not cross the divided place as much as possible, and the return current path of the power supply and signal should not change too much. The requirement that the digital-analog signal traces cannot cross is because the return current path of the digital signal with a faster speed will flow back to the source of the digital signal along the ground near the bottom of the trace as much as possible. If the digital-analog signal traces cross, the current will be returned. The generated noise will appear in the analog circuit area.

-The analog circuit uses star grounding. The current consumption of audio power amplifiers is generally very large, which may have an adverse effect on their own grounding or other reference grounds.

· Turn all unused areas on the PCB circuit board into a ground plane. Realize grounding coverage near the signal traces to shunt the excess high-frequency energy in the signal lines to the ground through capacitive coupling.

Shouldn't

-Use a hybrid circuit on the board. Although the radio frequency area of a mobile phone is generally considered to be analog, the noise coupled from the radio frequency area into the audio circuit will be demodulated into audible noise.

-The analog audio signal wiring is too long. Analog audio traces that are too long may be interfered by noise from digital and RF circuits.

-Forget the importance of ground loops. Poorly grounded systems will have serious distortion, noise, crosstalk, and low RF PCB immunity.

-Interrupt the natural loop of digital current. This path produces the smallest loop area, which can reduce antenna influence and inductance effects.

-Neglect to place the bypass capacitor as close as possible to the power supply pin to be bypassed.