1. consider the bottom planning carefully.
The ideal underlying planning should divide different types of circuits into different regions.
2. use differential signals as much as possible.
Audio devices with differential inputs can suppress noise. The middle of the differential signal is usually not ground. Because of the application principle of differential signals, the most important point is to use the advantages of the mutual coupling of differential signals, such as magnetic flux elimination, noise immunity and so on. If the ground wire is added in the middle, the coupling effect will be destroyed.
There are two points in the wiring of differential pairs. One is that the length of the two lines should be as long as possible, and the other is that the spacing between the two lines (which is determined by differential impedance) remains unchanged, that is to say, to keep parallel. There are two parallel ways, one for the two lines in the same line layer (side-by-side), one for the two lines walking in the upper and lower adjacent two layers (over-under). In general, side-by-side has more ways to implement it.
3. isolation ground current to avoid digital current to increase analog circuit noise.
Basically, it is right to divide modules / numbers into isolation. It should be noted that the signal should not cross the line as far as possible, but also don't let the return current path of the power and signal change too much. The analog signal line cannot cross is required because the digital signal slightly faster the return current path will try to go along the line near the lower part of the source of flowing into the digital signal, if the analog signal line cross, noise generated by the return current will appear in analog circuit area.
Analog circuits use star shaped grounding. The current consumption of audio power amplifiers is very large, which may have a negative impact on their own grounding or other reference grounding.
The unused area of the circuit board is turned into ground. The ground coverage is implemented near the signal line to shunt the excess high frequency energy to the ground through capacitive coupling.
Mobile phone circuit board design improves audio performance should not:
4. 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 radio frequency band coupled to the audio circuit will be demodulated as audible noise.
5. analog audio signal wiring too long.
Too long analog audio traces may be subject to noise from digital and radio frequency circuits.
6. forget the importance of grounding loop.
The bad grounding system will cause serious distortion, noise, crosstalk and low frequency interference immunity.
7. interrupt the natural loop of digital current.
This path produces the smallest loop area, which can reduce the antenna effect and inductance effect.
8. neglected to place the bypass capacitor in the position of the power pin that may be close to the bypass.