Crystal oscillator-free realization circuit and method for USB host interface

Abstract

A crystal oscillator-free realization circuit for a USB (Universal Serial Bus) host interface comprises an output capacitorless LDO (Low Drop Out Regular), an RC (Resistor-Capacitor) oscillator connected with the output capacitorless LDO, a phase-locked ring connected with the RC oscillator, a clock self-calibrating module connected with the phase-locked ring circuit and an external clock reference, wherein the phase-locked ring circuit comprises a phase-locked ring simulation circuit, a multi-phase clock generation circuit connected with the phase-locked ring simulation circuit, a programmable loop frequency divider connected with the multi-phase clock circuit and a comparison generation circuit connected with the phases-locked ring simulation circuit; the clock self-calibration module comprises a frequency comparison unit, an arbitration circuit connected with the frequency comparison unit, a frequency division coarse tuning adding and subtracting unit connected with the arbitration unit, a frequency division fine tuning adding and subtracting unit connected with the arbitration unit and a memory unit. The invention further provides a crystal oscillator-free realization method for the USB host interface. According to the crystal oscillator-free realization method and system disclosed by the invention, the use cost of the external oscillator crystal is saved.

Description

technical field [0001] The invention relates to the design of a USB interface, in particular to a crystal oscillator-free realization circuit and method of a USB1.1 / 2.0 host interface based on an RC oscillator and a phase-locked loop. Background technique [0002] The USB protocol points out that when the USB interface is transmitting data, the USB host will send a synchronization packet to the device, and the synchronization packet can play the role of clock synchronization. Generally speaking, as a USB host that provides a synchronous clock, it needs to generate an accurate and stable system clock source. The clock source should have the following characteristics: a) accurate clock frequency; b) low-temperature drift of clock frequency; c) High power supply rejection ratio for clock frequency. In most current applications, a crystal oscillator is generally used as the input clock source to generate the system clock source. However, with the intensified price competition ...

AI Technical Summary

Problems solved by technology

However, the LC oscillator requires a larger layout area, which even exceeds the layout area of ​​the USB1.1 / 2.0 host interface itself, which is not conducive to reducing costs; on the other hand, the LC oscillator requires high power consumption. Power consumption accounts for a large proportion of the total power consumption of the USB1.1 / 2.0 host interface

[0004] The RC oscillator has the characteristics of low cost, easy implementation, and low power consumption, but the traditional RC oscillator is not suitable for the input clock source of the USB1.1 / 2.0 host interface, because its clock frequency has a non-negligible temperature drift, and the circuit Some offset factors in the clock frequency will also have an important impact on the clock frequency. In addition, the traditional RC oscillation frequency has insufficient anti-power interference ability

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