Card reader is a common electronic device, widely used in identity identification, payment terminals and data transmission scenarios. Among them, the interface circuit is the key part of data exchange and communication. The main function of the interface circuit is to complete the signal conversion and transmission between the card and the main control device. Depending on the card type, the interface circuit of the card reader can support a variety of communication protocols, such as the ISO 7816 protocol (for contact IC cards), the ISO 14443 protocol (for contactless RFID cards), and NFC technology.

A typical interface circuit consists of the following components:
Signal conditioning circuit: Used to adjust signal levels to ensure electrical compatibility between the card and the card reader. For example, the signal level of the card is converted to a standard level that the master chip can handle.
Power management circuit: to provide a stable working power supply for the card, especially in the RFID card reader, the function of the antenna part to provide energy through induction is key.
Communication module: The implementation of protocol layer communication, such as serial communication (UART, SPI, I²C) or wireless communication, to ensure data integrity and reliability.
Protection circuit: including overcurrent protection, ESD (electrostatic discharge) protection, etc., to ensure the stable operation of the card reader in a complex environment.

The interface circuit of modern card readers also supports versatility and modular design, which can be compatible with multiple types of cards, while improving data transmission speed and security. These characteristics make the interface circuit a crucial technical core in the card reader.