Digitally Controlled Oscillator With DAC Tuning for Fine Frequency Resolution
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Solution Overview
Problem
Conventional analog frequency synthesizers face challenges in reducing size, cost, and complexity while maintaining reliability, especially in RF circuitry for wireless devices, due to the need for multiple analog components and limited digital control over frequency resolution.
Innovation Solution
The development of digitally controlled oscillators (DCOs) with a digital-to-analog converter (DAC) to vary capacitance, combined with fractional-N phase-locked loops and sigma-delta modulators for residue cancellation, allows for fine and coarse frequency control in a fully digital framework, reducing analog components and enhancing programmability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional analog frequency synthesizers are used, then frequency generation is achieved, but size, cost, and complexity increase while reliability decreases
Solution Approach 1:
The patent replaces analog frequency synthesizer circuits with a digitally controlled oscillator (DCO) that uses digital control signals to adjust frequency. The DCO employs digital capacitance control through switched capacitor arrays, substituting analog continuous adjustment with digital discrete control, thereby reducing analog component count and improving reliability while maintaining frequency synthesis capability.
2Area of stationary object
If analog components are reduced in DCO design, then size and cost decrease, but frequency resolution control capability deteriorates
Solution Approach 1:
The capacitance control is segmented into multiple discrete capacitor banks with different weightings (e.g., binary-weighted or Gray-coded arrays). Each capacitor bank can be independently switched by digital control signals, enabling fine frequency resolution through digital combination of discrete capacitance steps. This segmentation allows precise frequency control without requiring large analog variable capacitors, thus reducing size while maintaining resolution.
3Adaptability or versatility
If digital control is implemented for frequency synthesis, then programmability improves, but analog-to-digital conversion complexity increases
Solution Approach 1:
The patent extracts the analog-to-digital conversion function from a separate complex ADC circuit and integrates it directly into the DCO's frequency control mechanism. The DCO uses a feedback loop where the output frequency is compared with a reference, and the phase/d frequency error is converted to a digital control word that directly adjusts the capacitor switching. This integration eliminates standalone ADC complexity while maintaining full digital programmability of the output frequency.
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
This approach results in smaller, more reliable, and cost-effective RF devices with improved frequency resolution and immunity to semiconductor process variations, while minimizing jitter and phase noise, and reducing power consumption.
Implementation Method 1
a resonant circuit including an inductor coupled in series with a first capacitor, a second capacitor coupled in parallel with the series-coupled inductor and first capacitor
Implementation Method 2
a digital-to-analog-converter (DAC) to vary a capacitance of the first capacitor. More particularly, the capacitance of the first capacitor is varied for relatively fine frequency control of the frequency of the output signal of the DCO
Data Source
AI summary
An apparatus includes a digitally controlled oscillator (DCO), which includes an inductor coupled in series with a first capacitor. The DCO further includes a second capacitor coupled in parallel with the series-coupled inductor and first capacitor, a first inverter coupled in parallel with the second capacitor, and a second inverter coupled back-to-back to the first inverter. The DCO further includes a digital-to-analog-converter (DAC) to vary a capacitance of the first capacitor.