Digital DCO Gain Calibration With Tuning-Word Dithering
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Solution Overview
Problem
Deep-submicron CMOS processes pose challenges in integrating analog and RF circuits due to nonlinear frequency vs. voltage characteristics, low voltage headroom, and susceptibility to noise, making traditional analog circuits difficult to implement effectively, especially in RF synthesizers which require low-cost, low-power, and low-voltage monolithic solutions with stringent phase noise and switching speed requirements.
Innovation Solution
An all-digital frequency synthesizer architecture using a digitally controlled oscillator (DCO) tuned by a digital tuning word, with dithering of the tuning word applied to switchable devices within the DCO to achieve fine frequency resolution and low spurious content, while minimizing thermal noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional analog circuits are used in deep-submicron CMOS processes, then RF performance can be achieved, but manufacturing precision deteriorates due to nonlinear frequency vs. voltage characteristics and susceptibility to noise
Solution Approach 1:
The patent replaces traditional analog voltage-controlled oscillators with a digitally controlled oscillator (DCO) that uses digital tuning words to control frequency. This substitution of digital control for analog voltage control eliminates the nonlinear frequency-voltage characteristics and noise susceptibility of analog circuits while maintaining RF performance requirements.
Solution Approach 2:
The patent changes the control parameter from analog voltage to digital tuning words. The DCO responds to digital tuning words rather than analog voltages, fundamentally changing how frequency is controlled and eliminating the manufacturing precision issues associated with analog voltage control in deep-submicron CMOS processes.
2Ease of manufacture
If analog RF circuits are integrated into deep-submicron CMOS, then monolithic integration is achieved, but power consumption increases due to low voltage headroom and noise susceptibility
Solution Approach 1:
The patent substitutes digital circuitry for analog RF circuits, enabling full monolithic integration in deep-submicron CMOS without the power consumption penalties of analog circuits operating in low voltage headroom conditions. The digital DCO and associated circuitry are inherently more power-efficient in this process technology.
Solution Approach 2:
The patent creates a universal digital architecture that can be fully integrated in deep-submicron CMOS, where the same digital process technology is used for both digital baseband and RF functions. This eliminates the need for separate analog RF circuitry and its associated power consumption issues.
3Area of stationary object
If digital gates are increased to replace analog components, then silicon area is reduced, but device complexity increases
Solution Approach 1:
The patent replaces complex analog RF circuitry with digital logic circuits, reducing silicon area by eliminating large analog components such as inductors and precision analog circuitry. The digital DCO and control logic occupy significantly less area than their analog counterparts while achieving the same functional goals.
4Measurement precision
If frequency resolution is increased through fine tuning, then frequency precision is improved, but spurious content and thermal noise increase
Solution Approach 1:
The patent employs dithering of the digital tuning word to achieve fine frequency resolution. By periodically varying the tuning word and filtering the output, the system achieves high frequency precision while the periodic nature of the dithering helps suppress spurious content and thermal noise through averaging effects.
Solution Approach 2:
The patent introduces dithering as an intermediary mechanism between the digital tuning word and the DCO frequency control. This intermediary process enables fine frequency resolution to be achieved without directly increasing spurious content or thermal noise, as the dithering signal acts as a mediator that smooths the frequency transitions.
Data Source
AI summary
An all-digital frequency synthesizer architecture is built around a digitally controlled oscillator (DCO) that is tuned in response to a digital tuning word (OTW). In exemplary embodiments: (1) a gain characteristic (KDCO) of the digitally controlled oscillator can be determined by observing a digital control word before and after a known change (Δfmax) in the oscillating frequency; and (2) a portion (TUNE_TF) of the tuning word can be dithered (1202), and the resultant dithered portion (dkTF) can then be applied to a control input of switchable devices within the digitally controlled oscillator.