PLL Oscillator Capacitor Calibration for Accurate Frequency Modulation
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Solution Overview
Problem
Phase-locked loop circuits, particularly those used in range sensing applications, face challenges in achieving high accuracy in frequency-modulated signals due to deviations and errors, which affect distance measurements.
Innovation Solution
A method and oscillator design that utilize a bank of capacitors and a control unit to switch capacitors, determine frequency information, and write it to a look-up table, enabling precise control of frequency-modulated signals by accounting for nonlinearities and temperature drift during calibration and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase-locked loop circuit uses a frequency-modulated oscillator for range sensing applications, then distance measurements can be performed, but deviations and errors in the linearly frequency-modulated signals reduce measurement accuracy
Solution Approach 1:
The patent applies preliminary action by performing calibration before actual operation. During calibration mode, the system pre-determines frequency information for each capacitor state and stores it in a look-up table. This preliminary characterization of the oscillator's frequency behavior allows the system to compensate for deviations and errors during actual range sensing operations, thereby improving distance measurement accuracy without requiring real-time corrections
Solution Approach 2:
The patent implements feedback by using the determined frequency information from calibration to correct and compensate for signal deviations during operation. The control unit retrieves stored frequency information based on current capacitor states and uses this feedback to adjust frequency control signals, ensuring that the oscillator produces accurate linearly frequency-modulated signals despite manufacturing variations and environmental conditions
2Adaptability or versatility
If the oscillator switches capacitors to change output frequency, then frequency modulation is achieved, but nonlinearities and temperature drift cause deviations from ideal linear frequency modulation
Solution Approach 1:
The system performs preliminary measurement and characterization of the oscillator's frequency behavior for each capacitor switching state during calibration mode. This pre-determination of frequency information captures the actual nonlinear behavior and temperature drift characteristics, allowing the control unit to compensate for these deviations during operation by retrieving appropriate correction data from the look-up table
Solution Approach 2:
The patent applies parameter changes by storing multiple frequency information values in the look-up table corresponding to different capacitor states and operating conditions. The control unit dynamically selects and applies the appropriate frequency compensation parameters based on the current capacitor configuration and operating conditions, thereby maintaining accurate linear frequency modulation across varying parameters
Data Source
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AI summary
A method of controlling a frequency-modulated oscillator 110 of a phase-locked loop circuit 100 is described, wherein the oscillator 110 comprises a bank of capacitors 413. The method comprises the steps of (i) switching a capacitor 414 of the bank of capacitors 413 to change an output frequency 1050 of an output signal 112 of the oscillator 110 from a first frequency 1051 to a second frequency 1052, (ii) determining a frequency information associated with the capacitor 414 and based on at least one of the first frequency 1051 and the second frequency 1052; and (iii) writing the frequency information to a look-up table 224, 225, 226 stored in a control unit 120 of the oscillator 110. A corresponding frequency-modulated oscillator 110 and phase-locked loop circuit 100 are also described.