Mobilephone circuit board design to improve audio performance should:
1. Carefully consider the underlying planning.
Ideal bottom-level planning should divide different types of circuits into different regions.
2. Use differential signals whenever possible.
Audio devices with differential input can suppress noise. Differential signals can not be grounded in the middle. Because the most important point of the application principle of differential signals is to utilize the benefits of mutual coupling between differential signals, such as magnetic flux elimination, anti-noise ability and so on. If ground wire is added in the middle, the coupling effect will be destroyed.
There are two points to be noticed in the wiring of differential pairs. One is that the length of two lines should be as long as possible, and the other is that the distance between two lines (which is determined by differential impedance) should remain constant, that is, to keep parallel. There are two parallel ways, one is to walk two lines in the same side-by-side layer, the other is to walk two lines in the upper and lower adjacent two layers (over-under). Generally, the former side-by-side is implemented in many ways.
3. Isolate grounding current to avoid digital current increasing the noise of analog circuit.
Basically, it's right to isolate analog/digital partitions. Attention should be paid to signal routing as far as possible not to cross the partitioned area, and do not let the power supply and signal return current path change too much. The requirement that the digital and analog signals can not be crossed is that the return current path of the faster digital signals will flow back to the source of the digital signals as far as possible along the ground near the bottom of the line. If the digital and analog signals are crossed, the noise generated by the return current will appear in the analog circuit area.
The analog circuit uses star grounding. Audio power amplifiers generally consume a large amount of current, which may have adverse effects on their own grounding or other reference grounding.
Turn unused areas on the circuit board into grounding surfaces. The grounding coverage is realized near the signal line to distribute the excess high frequency energy in the signal line to the earth through capacitive coupling.
Mobilephone circuit board design should not improve audio performance:
4. Use hybrid circuit on board.
Although the RF area of mobile phones is generally considered analog, the noise coupled from the RF area to the audio circuit is demodulated to audible noise.
5. Analog audio signal wiring is too long.
Too long analog audio tracks may be disturbed by noise from digital and radio frequency circuits.
6. Forget the importance of grounding circuit.
Serious distortion, noise, crosstalk and low RF immunity will occur in systems with poor grounding.
7. The natural circuit of interrupting digital current.
This path produces the smallest ring area, which can reduce the antenna and inductance effects.
8. The bypass capacitance is neglected to be placed as close as possible to the power pin of the bypass capacitor.
Method of Improving Audio Performance in Mobile Phone Circuit Board Design
2019 09/17
