Digitally Controlled Oscillator Linearization With Feedback Mapping
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Solution Overview
Problem
Digitally controlled oscillators (DCOs) in mobile communication terminals face non-linearity issues due to external variations, leading to inconsistent code gain and potential data distortion, especially in direct modulation methods.
Innovation Solution
A negative feedback loop system is introduced, comprising a digital loop filter, frequency table, and frequency-to-digital code mapper, which corrects input signals to the DCO, ensuring linearity by storing and averaging frequency values and using them to adjust the input, thereby stabilizing the output frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DCO is used without a negative feedback loop, then the device complexity is low, but the code gain consistency deteriorates due to external variations
Solution Approach 1:
The patent implements a negative feedback loop that monitors the output frequency of the DCO and adjusts the input control word accordingly. A frequency-to-digital code mapper converts the output frequency back to a digital code, which is then compared with the input control word. The difference is used to generate a correction signal that compensates for non-linearity, ensuring consistent code gain across the entire control word range.
Solution Approach 2:
The patent introduces a frequency-to-digital code mapper as an intermediary component that bridges the output frequency domain and the input control word domain. This mapper acts as a mediator to provide feedback information about the actual output frequency, enabling the system to detect and correct deviations from the desired linear response without requiring direct measurement of the analog frequency.
2Object-generated harmful factors
If the code gain is not consistent, then the DCO can operate with simple structure, but the transmission distortion increases in direct modulation methods
Solution Approach 1:
The negative feedback loop continuously monitors the output frequency and adjusts the input control word to compensate for code gain variations. This feedback mechanism eliminates transmission distortion by ensuring that each control word increment produces a consistent frequency increment, which is critical for direct modulation methods where the control word directly modulates the carrier frequency.
3Reliability
If a negative feedback loop with frequency table and mapper is added, then the code gain consistency is improved, but the device complexity increases
Solution Approach 1:
The system uses its own output frequency information to generate the correction signal needed for linearization. The frequency-to-digital code mapper converts the output frequency back into a digital code that represents what the input control word should have been to achieve that frequency, allowing the system to self-correct its non-linearity without external calibration or complex lookup tables.
Data Source
AI summary
There is provided an apparatus for the linearization of a digitally controlled oscillator. The apparatus includes a first filter outputting only a low frequency band signal of an input signal to the digitally controlled oscillator; a negative feedback loop causing the signal of an input port of the digitally controlled oscillator to pass through a frequency table and a frequency-to-digital code mapper in sequence and correcting an input of the digitally controlled oscillator by performing negative feedback to an input port of the first filter; and a frequency table generator storing a frequency value of an output signal of the digitally controlled oscillator in the frequency table.