VCO Frequency Calibration Using Time-Digital Feedback
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Solution Overview
Problem
Wireless communication systems, particularly those using Orthogonal Frequency Division Multiplexing (OFDM), are sensitive to frequency synchronization errors caused by frequency mismatches in local oscillators, leading to performance degradation and equipment lifetime reduction, with existing high-precision oscillators being too expensive for civil applications.
Innovation Solution
A frequency calibration scheme for voltage-controlled oscillators (VCOs) using a frequency divider, time-digital converter, logic controller, and digital-to-analog converter, which measures time differences and adjusts control voltage to improve frequency accuracy without requiring an accurate VCO model, suitable for implementation on microcontrollers with limited computation capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If oven controlled oscillator (OCXO) is used to maintain constant temperature, then frequency accuracy is improved to several ppb, but device complexity, volume, and power consumption increase significantly
Solution Approach 1:
The patent replaces expensive OCXO with a cheaper temperature-compensated crystal oscillator (TCXO) combined with a digital calibration system. The TCXO provides sufficient baseline accuracy at lower cost, and digital calibration compensates for remaining errors through software algorithms rather than expensive hardware
Solution Approach 2:
The patent substitutes the mechanical/thermal compensation system (OCXO's oven heating mechanism) with an electronic/digital calibration system. Instead of physically maintaining temperature through heating elements and thermal control, the system uses digital signal processing and frequency calibration algorithms to achieve the same accuracy goal
2Measurement precision
If oven controlled oscillator (OCXO) is used to maintain constant temperature, then frequency accuracy is improved to several ppb, but power consumption increases due to heating requirements
Solution Approach 1:
The patent replaces the power-intensive OCXO heating system with a low-power TCXO and digital calibration approach. The TCXO consumes minimal power for temperature compensation, and the digital calibration performs accuracy enhancement through computation rather than continuous thermal energy input
3Ease of manufacture
If temperature-compensated crystal oscillator (TCXO) is used, then cost and power consumption are reduced, but frequency accuracy deteriorates compared to OCXO due to remaining sources of frequency offset
Solution Approach 1:
The patent introduces a digital calibration system as an intermediary between the TCXO and the final frequency output. The TCXO provides a good but not perfect frequency reference, and the digital calibration acts as a mediator to correct remaining errors from load capacitance, voltage variations, and manufacturing tolerances, achieving OCXO-level accuracy with TCXO hardware
Solution Approach 2:
The patent replaces the need for expensive OCXO hardware with a combination of TCXO hardware and digital calibration software. The digital processing substitutes for the thermal control mechanism, achieving frequency accuracy through computational correction rather than physical temperature control
4Measurement precision
If crystal oscillator parameters are made consistent through manufacturing, then frequency accuracy is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent implements a digital calibration system that measures actual frequency deviations and applies corrective adjustments. Instead of requiring perfect manufacturing consistency, the system uses feedback to detect and correct frequency errors caused by manufacturing variations, load capacitance differences, and voltage tolerances
Solution Approach 2:
The patent changes the approach from controlling physical manufacturing parameters to adjusting operational parameters through digital calibration. Rather than ensuring consistent capacitor values and component tolerances during manufacturing, the system adjusts frequency calibration parameters in software to compensate for manufacturing variations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed method improves frequency accuracy from ±20 ppm to ±10 ppb, offering a lightweight and cost-effective calibration solution for VCOs, suitable for consumer electronics and IoT devices.
Implementation Method 1
time-digital converter is used to measure the time difference of at least two continuous or discontinuous frequency division signals and obtain the actual time period of frequency division signal
Implementation Method 2
logic controller is used to generate the control voltage according to the difference between the actual time period of the frequency division signal and the calibration period of the frequency division signal, and adjust the frequency of the VCO according to the control voltage
Data Source
AI summary
The present disclosure provide a device, method and storage medium for frequency calibration for voltage-controlled oscillators. The device includes: A frequency divider connected with a VCO, a time-digital converter connected with the frequency divider, a logic controller connected with the time-digital converter, a digital-to-analog converter connected with the voltage-controlled oscillator; The frequency divider is used to divide the signal generated by the voltage-controlled oscillator into N times to get the frequency divider signal; Time-digital converter is used to measure the actual time period of frequency division signal; And the logic controller is used to generate the control voltage according to the difference between the actual time period of the frequency division signal and the calibration period of the frequency division signal, and adjust the frequency of the VCO according to the control voltage. The frequency precision of VCO is improved and the model-free adaptive frequency calibration of VCO is realized.