Digital headsets and analog headsets
Analog earphones are our common 3.5mm interface earphones, including left and right channels, ground or mic, as shown on the left.
The digital earphone (pictured on the right) contains a usb sound card + DAC&&ADC+amp+ analog earphone. When the digital earphone is connected to the mobile phone (otg) or computer, the mobile phone or computer recognizes the usb device and creates the corresponding sound card, and the digital audio signal passes After the usb is transmitted to the digital earphone, the digital earphone converts and amplifies the signal through the DAC, and then the sound can be heard. This is also the principle of the usb sound card.
The typec earphone (middle picture) may be an analog earphone or a digital earphone. It is judged by whether there is a chip in the earphone. I bought a digital headset on Taobao (the product introduced is a digital headset). After I bought it, the mobile phone could not be used, and the USB device could not be recognized by the computer. Later, I discovered that it was an analog headset with a typec interface, which was a serious false propaganda.
The difference between analog and digital headsets in mobile phones
DAC: Digital to analog converter
AMP: amplifier
TRS: (Tip, Ring, sleeve), refers to the audio plug, refer to https://wenku.baidu.com/view/3e0881741a37f111f0855b34.html
Typec headset introduction
Headphone interface diagram of common typec interface solutions on the market.
Figure 5 is the bottom view of the Mi 6x. The cancelled 3.5mm headphone jack is compatible with digital and analog headphones. This type of models includes Mi note3, Huawei p20pro, Nut Hammer, etc. (digital headphones are a USB slave device).
The circuit board is designed with a headset automatic switching ic (the left and right channels of the analog headset are connected to usb+, usb-, so you need to switch the light, such as DIO3202A, the vbus level is high, the chip is switched to the usb channel, the vbus level is low, switch To the earphone channel), after the digital earphone is connected to the earphone, the typec logic chip detects the slave device, the usb on the cpu switches to the master mode, and provides 5v (vbus) to power the slave device to complete the corresponding digital signal transmission.
Compatible with the principle of analog earphones, the typec logic chip will identify different devices (digital earphones, usb devices, analog earphone audio accessories) (mic can also be used to identify the principle of earphone plugging and unplugging: after the analog earphone is connected to the earphone, because the vbus is out of power, The headphone logic ic selects the headphone channel, and the headphone mic detection pin is initialized to high. When the analog headphone is inserted, the mic is equivalent to a 1k resistance. Due to the partial pressure, the voltage of the mic pin will be pulled down, and the internal voltage on the pmic where the mic_det pin is located The comparator detects the level change and further triggers the interruption of the earphone mic, and further determines the type of earphone, so as to identify the earphone).
The mobile phone shown in Figure 6 retains a 3.5mm headphone jack. Representative models include Huawei nova2s, Xiaomi 5x, etc. The typec interface of this type of model can be connected to digital earphones, but you can listen to music on nova2s, but the earphones cannot be used when making a call. This is because the corresponding channel support is required in the call scene (related to the cpu, please refer to https:/ /www.synopsys.com/zh-cn/china/resources/dwtb/dwtb-cn-usb-audio-2017q2.html ).
Figure 6 (Retain 3.5mm interface)