CPU Internal Loop Clock Output for Crystal Frequency Calibration
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Solution Overview
Problem
Current methods for calibrating crystal frequency offset, such as direct measurement using an oscilloscope or frequency meter, are inaccurate due to the influence of load capacitance, leading to unstable systems and affected RF performance.
Innovation Solution
A method involving an internal loop of a CPU that outputs an oscillation signal to a crystal circuit, producing a clock signal, and using a frequency meter to measure it without affecting the load capacitance, allowing for accurate calibration by regulating capacitance values in the crystal circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If direct measurement of clock frequency is performed using an oscilloscope or frequency meter on the transistor pin, then the measurement process is simple, but the load capacitance is affected leading to inaccurate measurement results
Solution Approach 1:
The patent introduces an intermediary measurement approach by measuring the clock frequency through the CPU's internal loop output rather than directly at the transistor pin. The CPU acts as an intermediary that buffers the measurement process, preventing the frequency meter from directly loading the crystal circuit. This resolves the contradiction by maintaining measurement simplicity while eliminating the harmful loading effect that degrades accuracy.
2Measurement precision
If the oscilloscope probe is connected to measure clock frequency, then the measurement can be performed, but the probe affects the load capacitance causing large frequency offset
Solution Approach 1:
The CPU's internal loop serves as an intermediary measurement interface that decouples the measurement instrument from the crystal circuit. By outputting the clock signal through the CPU's internal loop to an external pin, the system enables frequency measurement without the probe directly loading the crystal, thus maintaining both measurement capability and system stability.
3Ease of manufacture
If experience-based design of crystal clock and external load capacitance is used, then the design process is straightforward, but it is difficult to meet high precision clock requirements
Solution Approach 1:
The patent implements a feedback-based calibration method where the clock frequency is measured through the CPU's internal loop, the measured value is compared against the target frequency, and the load capacitance values are adjusted accordingly. This closed-loop feedback process enables precise clock frequency adjustment while maintaining design simplicity, resolving the contradiction between ease of manufacture and manufacturing precision.
Data Source
AI summary
The invention provides a method for calibrating crystal frequency offset through an internal loop of a central processing unit (CPU), which comprises: outputting an oscillation exciting signal to a crystal circuit by the CPU; producing a clock signal by the crystal circuit; outputting the clock signal through an output port arranged on the CPU by the internal loop; and adopting and connecting a frequency meter to the output port, and receiving and testing the clock signal to obtain a testing result; determining whether a deviation of the clock signal is qualified; if it is qualified, the tester exits subsequently, otherwise the tester regulates the crystal circuit, and then turning to Step S4. The clock signal of the CPU is output at the output port through the internal loop, and then the frequency meter is used for measuring the clock without being influenced by a probe, and the measurement is more accurate.