USB Device Frequency Calibration via Polling Signal
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Solution Overview
Problem
The high cost of producing USB 3.0 devices is attributed to the large chip area occupied by precise inductor capacitor (LC) oscillators, which are necessary for generating a precise reference clock for high-speed data transmission.
Innovation Solution
A frequency calibration method using a polling low frequency periodic signal to calibrate a programmable oscillator in a USB device, allowing it to generate a target oscillating signal with a predetermined frequency, thereby reducing the need for a built-in LC oscillator and lowering production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a precise inductor capacitor oscillator is built in a USB 3.0 device to generate a precise reference clock, then the frequency precision is improved, but the chip area occupied increases and production cost increases
Solution Approach 1:
The patent introduces an external host device as an intermediary to provide the reference clock signal. Instead of generating the reference clock internally with an LC oscillator, the USB device receives a polling low frequency periodic signal from the host, which serves as an external reference. This mediator approach allows the USB device to achieve precise frequency calibration without needing a large internal LC oscillator.
Solution Approach 2:
The patent uses a programmable oscillator that can be calibrated to copy the frequency characteristics of the external reference clock. By calibrating the programmable oscillator against the polling signal from the host, the device creates a local copy of the reference frequency, eliminating the need for a physical LC oscillator while maintaining frequency precision.
2Measurement precision
If a precise inductor capacitor oscillator is built in a USB 3.0 device to generate a precise reference clock, then the frequency precision is improved, but the production cost increases
Solution Approach 1:
The patent replaces the expensive LC oscillator with a programmable oscillator that can be calibrated using software/firmware. The polling low frequency periodic signal from the host serves as a temporary but sufficient reference during calibration. This approach uses cheaper components and shifts the precision requirement to the calibration process rather than the hardware oscillator.
Solution Approach 2:
The patent changes the approach from hardware-based frequency generation to software-controlled frequency calibration. By modifying the calibration parameters through the polling mechanism and adjusting the programmable oscillator's frequency divider settings, the system achieves precise frequency control without relying on expensive LC oscillator hardware.
3Area of stationary object
If a polling low frequency periodic signal is used to calibrate a programmable oscillator, then the chip area is reduced and production cost is lowered, but the device complexity increases
Solution Approach 1:
The patent makes the USB device's programmable oscillator multi-functional by using it both as a free-running oscillator and as a calibrated reference clock source. The same oscillator circuit serves dual purposes: generating initial clock signals and providing precise reference frequency after calibration. This universality reduces the need for separate dedicated calibration hardware.
Solution Approach 2:
The patent implements a feedback mechanism where the USB device measures the actual frequency of the polling signal from the host and uses this information to adjust its programmable oscillator's division ratio. The device counts the number of oscillating signal cycles during a specific clock period and uses this feedback to calculate the appropriate frequency divider setting, creating a self-calibrating system.
Data Source
AI summary
A frequency calibration method applicable in a Universal Serial Bus device includes: plugging the Universal Serial Bus device to a Universal Serial Bus host; using the Universal Serial Bus device to receive a polling low frequency periodic signal generated from the Universal Serial Bus host; determining a host type of the Universal Serial Bus host according to the polling low frequency periodic signal; and calibrating a programmable oscillator of the USB device according to a specific clock period corresponding to the host type, to make the programmable oscillator generate a target oscillating signal having a predetermined frequency.