“In actual use, the feedback microphone or speaker has different degrees of rustling, which is caused by noise in the audio output signal analyzed by the voice module circuit. After circuit analysis, system software analysis and simulation verification analysis of the voice module, it is confirmed that the voice module has a design defect, and the voltage margin of the clock frequency is insufficient at high frequency, which leads to the disorder of the audio signal and the “rustle” of the speaker.
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In actual use, the feedback microphone or speaker has different degrees of rustling, which is caused by noise in the audio output signal analyzed by the voice module circuit. After circuit analysis, system software analysis and simulation verification analysis of the voice module, it is confirmed that the voice module has a design defect, and the voltage margin of the clock frequency is insufficient at high frequency, which leads to the disorder of the audio signal and the “rustle” of the speaker. Through the software design of the voice module to reduce the clock frequency and improve the detection method, the reliability of the overall use of the voice module is improved.
introduction
There are various control platforms in the human-computer interaction mode, and its function is mainly to realize the communication between humans and machines. The devices that realize human-computer interaction in air conditioners in household appliances are mainly remote controllers, handheld devices, touch screens and other devices. With the continuous development of computer technology, people’s needs are constantly increasing, and the functions that need to be controlled are getting stronger and stronger. , such as playing a popular song, the current weather state, telling a joke, the current date, etc., the operation instructions required for synchronization are also increasing, the traditional operation mode can no longer meet the needs of modern development, and the voice interaction mode stands out, it can identify people The language realizes the operation of various functions of the air conditioner, and provides feedback on the equipment output of the operation results. The highly integrated voice module combined with the functional characteristics of human-computer interaction has become the preferred choice for air conditioner products. Due to the complexity of its own hardware and software, the abnormality will affect the normal feedback of input and output signals, and will affect the user’s experience of using the air conditioner. Therefore, the problem of the reliability of the voice interaction platform needs to be studied and solved urgently.
1 Analysis of the cause and failure mechanism of the audio output noise of the voice module
In the production process of air conditioners, the introduction and use of the voice module of manufacturer A resulted in many complaints and accidents during the actual production and user use. It was reported that the voice broadcast of the air conditioner failed and abnormal voice control occurred. The failed voice module was powered on and the test fault recurred. There is a rustling sound in the speaker broadcast, as shown in Figure 1, the voice module PCBA.
Figure 1 Voice module PCBA
The rustling sound of the voice module is mainly caused by the abnormal output of the audio signal. The possible reasons for the analysis include the failure of the audio output circuit device, abnormal failures such as welding, or abnormal software, resulting in the rustling of the output audio signal.
1.1 Appearance and welding inspection of voice module
Use a magnifying glass to observe the faulty voice module without damage to components and abnormal welding, X-RAY scanning did not find abnormal welding, and no assembly problems were found in the visual inspection, as shown in Figure 2.
Figure 2 Visual inspection (left), X-RAY scan (middle, right)
1.2 Power-on test electrical performance parameters
For the power-on test of the failed voice module, the rustling sound of the fault recurs during the voice interaction test, and the voltage and current values of the key performance parameters of the voice module are within the normal range, as shown in Figure 3.
1) Current parameters: the actual test value of the current when the whole machine is running is 264 mA, which meets the requirements in the range of 170~270 mA;
2) Power supply voltage parameters: The actual test value of the 5 V power supply voltage is 5.22 V, which meets the required range of 4.6~5.5 V;
3) MIC voltage parameters: The actual test value of the MIC voltage is 3.32 V, which meets the required range of 1.7~3.6 V.
Figure 3 Power-on test of the voice module
1.3 Key port parameter test
Test the PN value of the speaker, communication and microphone ports of the faulty product and compare it with the normal product. The test results are consistent, and no abnormality is found, as shown in Table 1.
Table 1 PN value of each port parameter test 
1.4 Anti-interference test
For the external electromagnetic signal interference test verification, no abnormality was found through the verification without a magnetic ring and near a strong electric field (as shown in Figure 4).
1) The voice module can work normally without the addition of the magnetic ring, and there is no broadcast abnormality in the test for 30 minutes.
2) The whole machine is assembled and used the voice module, and the power line is placed in the attachment of the main board, and the whole machine does not add a magnetic ring to verify that the voice function is normal, and no sound failure occurs within 30 minutes of the test.
Figure 4 Power-on verification of the voice module installed in the whole machine (strong wires are placed on the left, and no magnetic ring is added to the right machine)
1.5 Waveform Test
1) Speaker waveform test
The abnormal speaker waveform output is abnormal, the amplitude is too large, and the peak-to-peak value is clutter of 8.2 V. The normal waveform is an orderly sine wave with an amplitude between 3.16 and 3.3 V, as shown in Figure 5 (the left picture is the abnormal product waveform). , the picture on the right is the normal waveform):
Figure 5 Speaker waveform output test
2) Chip DAC waveform test
Under normal working conditions, the output waveform of the chip DAC is normal, as shown in Figure 6.
Figure 6 Normal chip DAC output waveform
When the speaker appears “rustling”, the output waveform of the chip DAC has been abnormal, and obvious noise can be seen, which is consistent with the waveform output of the abnormal speaker, as shown in Figure 7.
Figure 7 Abnormal chip DAC output waveform
3) The chip DAC is integrated in the MCU main control, and it is analyzed that the failure factor of rustling sound broadcast by the speaker of the voice module is related to the MCU main control chip, as shown in Figure 8.
Figure 8 Voice module architecture
1.6 Voice Module Logic Voltage Test
Test the Logic voltage of the MCU main control chip of the voice module. It is found that the corresponding VDD_LOG voltage in the PCBA is abnormal compared with the normal product, and the abnormal rustling sound is generally low.
Figure 9 Circuit diagram where VDD_LOG is located
After testing the VDD_LOG voltage, the after-sale faulty voltage is 0.946 V, and the qualified voltage is 1.105 V. Through the voltage test comparison, it is found that the qualified VDD_LOG voltage is about 1.1 V, and the faulty product VDD_LOG voltage is below 1.0 V.
2. Simulation and reproduction of noise failure simulation experiment of voice module
2.1 Configure the Logic voltage on the PCBA of the faulty product, and perform a frequency reduction test:
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