Patent ID: 8656205

Claim:
A universal serial bus (USB) device with a clock calibration function, comprising: a first controller, arranged to generate a first operating clock according to a first reference clock; a second controller, arranged to generate a second operating clock according to a second reference clock; a calibration circuit, comprising: a first calibration unit, coupled to the first controller, arranged to generate a first control signal according to the first operating clock; and a second calibration unit, coupled to the second controller, arranged to generate a second control signal according to the second operating clock; and a selecting circuit, coupled to the first calibration unit and the second calibration unit, arranged to select a target control signal from the first control signal and the second control signal; and an embedded oscillator (EMOSC), coupled to the selecting circuit, the first controller, and the second controller, arranged to output the first reference clock to the first controller or output the second reference clock to the second controller according to the target control signal; wherein during a first phase, a first calibration is performed on the USB device via the first calibration unit in order to control the EMOSC to output the first reference clock to the first controller; during a second phase, a second calibration is performed on the USB device via the second calibration unit in order to control the EMOSC to output the second reference clock to the second controller.