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Resolution direction of power amplifier bottom noise

Time:2023-03-11 Views:1393

 Generation of bottom noise

Generally, the bottom noise of mass produced chips is the normal value, hundreds of micro-amplitude, but in actual use, there will be various kinds of bottom noise. First, judge how the bottom noise is generated. There are three types of bottom noise:

1、 Chip‘s own bottom noise: Generally speaking, the chip‘s own bottom noise in mass production is normal.

2、 The bottom noise of the sound source, due to the poor processing of the board, causes the sound source itself to carry interference signals, which are transmitted to the power amplifier and output by the power amplifier, resulting in the bottom noise. (More common)

3、 The bottom noise caused by power supply or GND, dirty power supply or fixed frequency jitter can also cause the bottom noise, which usually occurs in DC-DC. (More common), GND interference can also cause background noise

 Determine the generation of bottom noise

1、 Judge the bottom noise of the chip itself: shorten the output of the power amplifier to GND. If the bottom noise is normal, it is likely that the sound source has the bottom noise.

2、 Sound source bottom noise: use the oscilloscope to test the sound source signal, and you can see whether there is too much noise, and then connect the earphone to the sound source, and listen whether the sound source has bottom noise.

3、 Bottom noise caused by power supply or GND: use an oscilloscope to test whether the power supply is clean and whether there is a fixed frequency string in the power supply. There is a requirement for the oscilloscope bandwidth. If the GND is not clean, it will string into two places. The power ground inside the chip will cause the power supply inside the chip to be dirty, resulting in the bottom noise. In addition, if it is a single-ended input power amplifier, it will enter the reference point of the amplifier inside the chip through the BYPASS capacitor. If the reference point has interference, it will generate the bottom noise.

 Solution direction of bottom noise

Sound source bottom noise: find the reason from the sound source. If the master control has differential output, use differential output to eliminate interference. If there is no difference, check whether the frequency device is too close to the analog signal, etc.

Power supply and GND bottom noise: start with power supply interference, add capacitance and π type filter circuit to eliminate interference or change the frequency beyond the audio range. If GND has interference with single-ended input, BYPASS capacitance should be increased from BYPASS, or a small resistance test should be conducted in series, and then the chip audio circuit should be separated from the ground of other signals separately.

The magnetic bead can also be used according to the actual situation. The parallel connection of resistance and capacitance should not be too large to isolate low-frequency interference. The resistance should not be too large. Generally, it is at ohm level. Too large resistance may cause jamming.

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