docs(audio): add adc mic hardware design reference

Author: loop233

docs/_static/audio/adc_mic_hardware_ref_design.png

@@ -15,6 +15,19 @@ Features
 Reference Circuit
 ------------------
 
+The external reference circuit is shown below. Customers can choose between transimpedance amplifier or inverting/non-inverting amplifier circuits to amplify the MIC input signal. For more design reference information about front-end MIC amplifiers, please refer to `Single-Supply, Electret Microphone Pre-Amplifier Reference Design <https://www.ti.com/lit/ug/tidu765/tidu765.pdf>`__.
+
+Notes:
+- Bias: The ADC side needs midpoint bias (such as Vref/2), and AC coupling on the op-amp output side to avoid DC saturation of the ADC.
+- Power supply: It is recommended to use LDO for MIC power supply regulation to avoid power supply fluctuations affecting ADC sampling. If external LDO is not used, please add separate RC filtering on the power supply side.
+- It is recommended to select MIC with sensitivity greater than -46dB to avoid ADC sampling errors due to insufficient MIC sensitivity. Adjust the amplification factor according to the microphone sensitivity.
+
+.. figure:: ../../_static/audio/adc_mic_hardware_ref_design.png
+    :align: center
+    :alt: ADC mic hardware reference design
+
+    ADC mic hardware reference design
+
 External Configuration for ADC Continuous
 ------------------------------------------
 

docs/en/audio/adc_mic.rst

@@ -15,6 +15,17 @@ ADC 麦克风
 参考电路
 ----------
 
+外部参考电路如下，客户可以选择跨阻放大器或者同相/反相放大电路对 MIC 输入信号进行放大。关于前端 MIC 放大器的更多设计参考信息，请参考 `Single-Supply, Electret Microphone Pre-Amplifier Reference Design <https://www.ti.com/lit/ug/tidu765/tidu765.pdf>`__。
+注意：
+- 偏置：ADC 端要有中点偏置（如 Vref/2），并在运放输出侧 AC 耦合，避免直流顶死 ADC。 
+- 电源：MIC 供电最好使用 LDO 进行稳压，避免电源波动影响 ADC 采样。如果不使用外部 LDO，请在电源侧进行单独的 RC 滤波。
+- 推荐选择灵敏度大于 -46dB 的 MIC，避免 MIC 灵敏度不足导致 ADC 采样误差。并根据麦克风的灵敏度调整放大倍数。
+
+.. figure:: ../../_static/audio/adc_mic_hardware_ref_design.png
+    :align: center
+    :alt: ADC mic hardware reference design
+
+    ADC mic hardware reference design
 
 外部配置 ADC Continuous
 --------------------------