Mobile phone series: Understand the difference between American standard and Chinese standard headphone jack in one article

Early 3.5mm headphones only had three PINs: GND, left and right channels. This headphone interface is simple and widely used. It is often found on audio interfaces of large devices such as computers. However, this interface has an obvious disadvantage: there is no MIC and you cannot record or make phone calls.

A MIC interface can be added separately on a computer, but on a highly integrated mobile device such as a mobile phone, adding a MIC interface separately takes up a lot of space and is obviously not a cost-effective solution. Therefore, a headphone interface with an integrated MIC has appeared.

At that time, each manufacturer was free to express itself, and a variety of headphone interfaces appeared. The headphone interfaces of different manufacturers were incompatible with each other, which brought a lot of trouble to consumers. The world has suffered from the complexity of headphone interfaces for a long time.

Therefore, a unified standard headphone interface is urgently needed.

Later, OMTP (national standard) and CTIA (American standard) appeared. The only difference between the two in the link is MIC and GND.

At that time, the famous Nokia followed OMTP. China also chose OMTP. However, Nokia, which was at its peak, soon fell from the altar and was surpassed by Apple. Apple chose the CTIA American standard. Because of this, many students at that time found that Android and Apple headphones were incompatible .

The advancement of technology has always served the needs of users. In order to solve the compatibility issues between national standards and American standards, audio switches began to enter people's field of vision. Current mobile phones usually have audio switches added. The path principle is shown in the figure below, blue and green curves.

When the earphones are plugged in, the pin order can be determined by detecting the impedance of MIC and GND. The audio switch will automatically switch the MIC and GND paths . No matter what standard of earphones are used or how they are plugged in, the two can be compatible.