Oscillator Nonlinearity Compensation for Constant PLL Gain
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Solution Overview
Problem
Oscillator circuits in applications like phase locked loops (PLLs) face challenges due to nonlinearities, which affect the linearity of the oscillator characteristic, leading to frequency modulation and demodulation inaccuracies in devices such as mobile communication devices.
Innovation Solution
A device comprising an oscillator circuit, a control circuit, a frequency detector circuit, and a processor circuit that estimates and compensates nonlinearities by calculating coefficients of a polynomial oscillator characteristic, using an equalizer circuit to generate an equalized frequency control signal that corrects for these nonlinearities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If oscillator circuit is implemented with practical components, then device complexity is reduced and ease of manufacture is improved, but oscillator characteristic linearity deteriorates due to nonlinearities
Solution Approach 1:
The patent introduces a polynomial model as an intermediary representation of the oscillator characteristic. By modeling the nonlinear relationship between frequency control input and oscillator frequency using polynomial coefficients, the system can accurately represent practical oscillator behavior while maintaining ease of manufacture. The polynomial model acts as a mediator between the physical oscillator circuit and the control system.
Solution Approach 2:
The patent changes the parameter representation from direct frequency control to polynomial coefficient representation. By determining polynomial coefficients through frequency measurements at different input values, the system transforms the oscillator characteristic into a manageable mathematical form that preserves linearity accuracy while allowing practical implementation with standard components.
2Manufacturing precision
If polynomial model with calculated coefficients is used, then oscillator characteristic linearity is improved, but device complexity and measurement requirements increase
Solution Approach 1:
The patent applies partial action by using a second-order polynomial model rather than a complete high-order model. This provides sufficient linearity correction for practical applications without the excessive complexity of higher-order models. The approach uses minimal frequency measurements (at least three different input values) to determine the necessary polynomial coefficients, avoiding unnecessary complexity.
Solution Approach 2:
The system performs self-characterization by automatically determining its own polynomial coefficients through frequency measurements. The oscillator circuit itself provides the data needed to model its nonlinear behavior, eliminating the need for external characterization equipment or complex calibration procedures. This self-service approach reduces overall device complexity.
3Manufacturing precision
If frequency measurements at multiple input values are performed, then polynomial coefficients are accurately determined improving linearity, but measurement time and productivity are reduced
Solution Approach 1:
The patent requires only the minimum necessary frequency measurements (at least three different input values) to determine second-order polynomial coefficients. This partial action approach provides sufficient accuracy for practical applications without performing excessive measurements that would reduce productivity. The method balances measurement effort with achievable linearity correction.
4Manufacturing precision
If equalizer circuit with nonlinear characteristic is used, then oscillator nonlinearities are compensated improving linearity, but device complexity increases
Solution Approach 1:
The equalizer circuit acts as an intermediary component that receives the frequency control input and transforms it according to the polynomial model before applying it to the oscillator. This mediator approach allows the use of a relatively simple equalizer circuit with nonlinear characteristic to compensate for oscillator nonlinearities, achieving linearity improvement without requiring complex active compensation mechanisms.
Data Source
AI summary
A device may include an oscillator circuit, a control circuit, a frequency detector circuit, and a processor circuit. The oscillator circuit may include a frequency control input to output an oscillator signal. The frequency of the oscillator signal depends on an input signal applied to the frequency control input. The control circuit is configured to apply a first input signal value, a second input signal value, and a third input signal value to the frequency control input. The frequency detector circuit is configured to detect the first frequency value of the oscillator signal when the first input signal value is applied to the frequency control input, a second frequency value of the oscillator signal when the second input signal value is applied to the frequency control input, and a third frequency value of the oscillator signal when the third input signal value is applied to the frequency control input.