Circuit and method for generating USB (universal serial bus) peripheral clock

Abstract

The invention discloses a circuit and a method for generating USB (universal serial bus) peripheral clock. The circuit comprises an internal oscillator, a controllable frequency divider, a frequency multiplier, a receiving timer and a frequency division controller, wherein the internal oscillator generates clock with fixed frequency, the controllable frequency divider carries out frequency division on the clock generated by the internal oscillator, the frequency multiplier carries out frequency multiplying on the clocked subjected to frequency division, in addition, the clock subjected to the frequency multiplying is transmitted to a USB main body structure, the receiving timer receives SOF (start-of-frame) data packets sent by a host machine according to the clock output by the frequency multiplier, in addition, the time intervals for receiving the SOF data packets are counted, the frequency division controller compares differences of the counting results of the receiving timer and the standard time intervals, and the frequency division perimeters of the controllable frequency divider are controlled and regulated according to comparison results. Through the technical scheme disclosed by the invention, under the condition without occupying lead pins of the USB main body structure, high-precision and accurate main clock is provided for the USB main body structure, and the high-speed communication of the USB main body structure is ensured.

Description

technical field [0001] The invention relates to the field of USB communication, and more particularly relates to a circuit and method for generating a USB peripheral clock. Background technique [0002] USB is the abbreviation of Universal Serial BUS in English, and the Chinese meaning is "Universal Serial Bus". Because of its fast communication speed, simple interface, and convenient application, USB has become one of the necessary standard interfaces for electronic devices such as PCs, MP4s, mobile phones, PDAs (Personal Digital Assistants, handheld computers), digital cameras, printers, and scanners. First, it has been widely used in information communication and data transmission. [0003] Conventional communication systems often require a relatively accurate clock source. Using this clock source, the main clock required for the communication system is generated through logic such as frequency division or frequency multiplication in the communication system, and the tra...

AI Technical Summary

Problems solved by technology

However, due to RC / LC oscillator process deviation or other factors, there is usually a ±20% deviation between the clock generated by the on-chip oscillator and the design target, which cannot meet the accuracy requirements of system transmission.

[0007] And because high-speed USB has higher requirements on peripheral clock accuracy than full-speed (communication speed is 12MHz) and low-speed (communication speed is 1.5MHz) devices, and the data code rate of high-speed USB peripherals is 480Mb, which is also higher than that of full-speed and low-speed USB peripherals. The device is too fast, so the clock generation circuit used for full-speed and low-speed USB peripherals is no longer suitable for high-speed USB peripherals

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