Crystal Frequency Offset Calibration via RF Signal
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Solution Overview
Problem
Existing methods for calibrating crystal frequency offset are inaccurate due to the influence of oscilloscope probes and frequency meters on load capacitance, making it difficult to achieve high precision in high-speed signal systems.
Innovation Solution
A method involving a radio frequency signal calibration process where a device under test is connected to a WLAN tester via a copper pipe connector, allowing users to test and regulate the crystal circuit without probe interference, using a test module and control terminal to assess and adjust the RF signal deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an oscilloscope probe is used to measure clock frequency on the transistor pin, then the measurement can be performed directly, but the probe affects the load capacitance and causes large frequency offset
Solution Approach 1:
The patent introduces an RF cable as an intermediary component to transmit the RF signal from the device under test to the WLAN tester. This mediator allows measurement without direct probe contact with the transistor pin, thereby avoiding the probe's capacitive loading effect that would otherwise distort the frequency measurement
Solution Approach 2:
The patent replaces the mechanical probe measurement system with an RF signal transmission system. Instead of using a physical oscilloscope probe to directly contact and measure the clock signal, the system uses RF cable transmission combined with WLAN tester measurement, substituting the mechanical measurement approach with an electromagnetic field-based measurement approach that avoids capacitive loading
2Measurement precision
If a frequency meter is used to measure clock frequency on the transistor pin, then the frequency can be measured, but the load capacitance is affected leading to inaccurate test results
Solution Approach 1:
The RF cable serves as an intermediary that transmits the RF signal without the measurement instrument directly contacting the transistor pin. This eliminates the frequency meter's impact on load capacitance while still enabling accurate frequency measurement through the transmitted RF signal
Solution Approach 2:
The patent replaces the direct frequency meter measurement with an RF signal transmission and measurement system. The measurement is performed on the RF signal after it has been transmitted through the cable, rather than directly on the clock signal at the transistor pin, thereby avoiding capacitive loading effects
3Ease of manufacture
If empirical values are used for crystal clock and external load capacitance design, then the design process is simplified, but high precision clock requirement cannot be met
Solution Approach 1:
The patent implements a feedback mechanism where the RF signal frequency is measured using the WLAN tester, and based on the measured frequency offset, the load capacitance is adjusted. This closed-loop feedback process allows the system to achieve high precision clock by iteratively correcting the frequency offset, rather than relying solely on empirical design values
Solution Approach 2:
The system performs self-calibration by measuring its own RF signal frequency and automatically adjusting the load capacitance to correct frequency offsets. This self-service capability enables the system to achieve high precision without requiring complex external calibration equipment or manual adjustments
Data Source
AI summary
A method for calibrating crystal frequency offset through a radio frequency signal includes, in Step S1, a radio frequency port of a device is connected to one end of a radio frequency cable through a copper pipe connector and the other end of the radio frequency cable is connected to a Wireless Local Area Network (WLAN) tester which is connected with a control terminal. In Step S2, a user controls the WLAN tester to test the radio frequency signal of the device through the control terminal to obtain a test result, and determines whether a deviation of the radio frequency signal is qualified. If it is qualified, the user exits the test, otherwise the user regulates the crystal circuit of the device under test, and returns to Step S2. The method may not be affected by a probe, thus the measurement may be more accurate.