Digital Controlled Oscillator Feedback for Stable RC Clock Accuracy
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Solution Overview
Problem
Fully integrated RC oscillators suffer from inferior performance compared to oscillators using high Q resonators, particularly in terms of frequency accuracy, temperature and voltage drift, and phase noise, but are desirable for their integration and cost benefits.
Innovation Solution
A digital controlled oscillator (DCO) with a programmable current source, variable capacitors, and a frequency monitor that adjusts the oscillation frequency based on feedback from comparing successive clock periods, using a clock divider and comparator to compensate for temperature and voltage-induced deviations, allowing for continuous and reliable frequency control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fully integrated RC oscillators are used instead of crystal oscillators, then device complexity and production costs are reduced, but frequency accuracy, temperature and voltage drift, and phase noise performance deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where the oscillator frequency is continuously monitored and compared against a reference frequency. A control signal is generated based on the frequency deviation and fed back to adjust the oscillation frequency, thereby maintaining high frequency accuracy while using integrated RC oscillators instead of crystal oscillators
Solution Approach 2:
The patent dynamically changes the oscillation parameters (frequency, amplitude) based on environmental conditions and load variations. By adjusting these parameters in real-time through control circuits, the system maintains optimal performance across different operating conditions, resolving the contradiction between integration benefits and performance stability
2Ease of manufacture
If fully integrated RC oscillators are used instead of crystal oscillators, then device complexity and production costs are reduced, but temperature and voltage drift increases
Solution Approach 1:
The control system continuously monitors frequency deviations caused by temperature and voltage variations and applies corrective feedback to maintain stable oscillation. This allows the use of cost-effective integrated RC oscillators while compensating for their inherent sensitivity to environmental changes
Solution Approach 2:
The system performs preliminary calibration and adjustment during initialization or manufacturing to pre-compensate for known temperature and voltage drift characteristics. This preliminary action reduces the burden on real-time control and lowers overall system complexity
3Measurement precision
If frequency monitoring and feedback adjustment circuits are added to the DCO, then frequency accuracy and stability are improved, but device complexity increases
Solution Approach 1:
The patent merges the frequency monitoring, comparison, and control functions into an integrated control unit that works closely with the oscillator circuit. By combining these functions rather than implementing them as separate discrete blocks, the system achieves high frequency accuracy while minimizing the increase in overall device complexity
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
The solution enhances the accuracy and long-term stability of the oscillation frequency, achieving precision comparable to crystal oscillators with reduced complexity and production costs, while maintaining a wide operating frequency range and efficient implementation.
Implementation Method 1
a first variable capacitor (C1) and a second variable capacitor (C2). A comparator (COMP) compares the voltage drop across the variable capacitors with a reference voltage level
Implementation Method 2
A comparator compares the voltage drop across the variable capacitors with a reference voltage level and provides a DCO output clock signal
Implementation Method 3
A switch alternately charges the variable capacitors from the programmable current source or discharges the variable capacitors in response to an output signal of the comparator
Implementation Method 4
The frequency monitor receives the divided clock signal. The frequency monitor determines the time difference of successive clock periods of the divided clock signal and generates a corresponding feedback signal
Data Source
AI summary
A digital controlled oscillator including a programmable current source, a first variable capacitor and a second variable capacitor. A comparator compares the voltage across the variable capacitors with a reference voltage level and generates a DCO output clock signal. A switching means alternately switches the variable capacitors to either charge from a programmable current source or discharge in response to an output signal of the comparator. A clock divider divides the DCO output clock signal by a factor N substantially greater than 1. A frequency monitor receives the divided clock signal, determines the time difference of successive clock periods of the divided clock signal and generates a feedback signal to adapt the frequency of the DCO output clock signal.