Crystal-free USB device clock calibration method and calibration circuit

Abstract

The invention relates to a crystal-free USB device clock calibration method and a calibration circuit, used for implementing the following steps: identifying and sampling an SOF packet on a USB bus, verifying the sampled SOF packet data, and outputting verification signals; counting the verification signals, comparing with a preset count value according to the counting result, and configuring a PLL parameter according to the comparison result; and clock-calibrating the RC oscillator of the USB internal clock and the PLL phase locked loop according to the PLL parameter. The invention has the beneficial effects that the information of the remainder part is retained, and the multi-phase sampling of the USB serial differential signal is carried out by using the fractional frequency dividing idea, so that the level characteristic of the USB serial differential signal can be accurately determined; all the information of the SOF packet is verified to ensure the reliability of SOF detection; the detection result will be more accurate; and in particular, the accuracy of the SOF packet detection of the invention is not affected by the internal clock bias to be calibrated.

Description

technical field [0001] The invention relates to a clock calibration method and a calibration circuit of a USB device without a crystal oscillator, belonging to the field of electricity. Background technique [0002] Due to its high versatility, strong scalability, simple interface, and convenient application, the USB interface has become one of the necessary standard interfaces for electronic equipment, and has been widely used in information communication and data transmission. The USB protocol has strict regulations on the rate of the interface signal. In the low-speed state, the data rate of the USB interface is 1.5MHz±1.5%, which is used in keyboards, mice, etc.; in the full-speed state, the data rate of the USB interface is 12MHz±0.25%, used in audio electronic equipment, etc., in the high-speed state Under the circumstances, the data rate of the USB interface is 480MHz±0.05%, which is applied to video-related electronic equipment. Therefore, in order to ensure the st...

AI Technical Summary

Problems solved by technology

However, in the complex environment of circuit work, there are various interferences on the signal on the USB bus, and the signal on the USB will be destroyed at a transient moment, resulting in the probability of misidentification or loss of SOF packets.

In addition, due to the instability of the internal oscillator clock frequency before calibration, there will be a large deviation in the sampling clock frequency, which will further increase the probability of identifying SOF packet errors

Images