Merge branch 'master' of github.com:m5stack/m5-docs

docs/en/unit/pdm.md

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 ## Description
 
-**PDM mini Unit** is a digital MEMS silicon-based microphone based on PDM (Pulse Density Modulation). The microphone has high signal-to-noise ratio, high sensitivity, low power consumption, anti-radio frequency interference, smooth frequency response and other characteristics. It automatically switches the microphone state according to the clock frequency (power down/activate/sleep)and can be widely used for audio data collection on wearable devices and smart digital devices.
+**PDM mini Unit** is a digital MEMS silicon-based microphone based on PDM (Pulse Density Modulation) signal. The microphone has high signal-to-noise ratio, high sensitivity, low power consumption, anti-radio frequency interference, smooth frequency response and other characteristics. It automatically switches the microphone state according to the clock frequency (power down/activate/sleep)and can be widely used for audio data collection on wearable devices and smart digital devices.
 
 ## Product Features
 

docs/en/unit/tvoc.md

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 ## Applications
 
 - Air quality monitoring
-- Formaldehyde detection
 - eCO2 concentration
 
 ## Specification

docs/zh_CN/unit/pdm.md

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 ## 描述
 
-**PDM mini Unit** 是一款基于PDM(脉冲密度调制)的数字式MEMS硅基麦克风，该麦克风具有高信噪比，高灵敏度，功耗低，抗射频干扰，频率响应平滑等特性，根据时钟频率自动切换麦克风状态(断电/激活/休眠)，可广泛用于可穿戴设备、智能数码设备的音频数据采集。
+**PDM mini Unit** 是一款基于PDM(脉冲密度调制)信号的数字式MEMS硅基麦克风，该麦克风具有高信噪比，高灵敏度，功耗低，抗射频干扰，频率响应平滑等特性，根据时钟频率自动切换麦克风状态(断电/激活/休眠)，可广泛用于可穿戴设备、智能数码设备的音频数据采集。
 
 ## 产品特性
 

docs/zh_CN/unit/tvoc.md

@@ -26,8 +26,7 @@
 ## 应用
 
 - 空气质量监测
-- 甲醛检测
-- eCO2浓度
+- eCO2浓度检测
 
 ## 规格参数