Programmable RC Oscillator Using Switched-Capacitor Delay Sections
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Solution Overview
Problem
Conventional RC oscillators face challenges in programmability due to difficulties in fabricating inductors on integrated circuits and the complexity of using variable resistors and capacitors, especially with 'floating' capacitors that swing across supply and ground voltages, limiting their frequency control and practicality in digital logic circuits.
Innovation Solution
The design incorporates a programmable oscillator circuit with a first delay section featuring a variable RC network and a second delay section with a fixed RC network, utilizing switched capacitors and control signals to set capacitance, allowing for on-the-fly frequency adjustment through a feedback loop, thereby overcoming the limitations of conventional RC oscillators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional RC oscillators use variable resistors or capacitors to achieve frequency adjustment, then frequency programmability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent implements a dynamically adjustable RC oscillator where the delay element's resistance or capacitance can be changed in real-time through digital control signals. This allows the oscillator frequency to be programmably adjusted without redesigning the entire circuit, resolving the contradiction between frequency adaptability and device complexity by enabling dynamic reconfiguration rather than requiring multiple fixed circuits.
Solution Approach 2:
The patent changes the physical parameters of the RC network by using switchable resistor or capacitor elements that can be programmed to different values. This allows the same physical circuit to operate at multiple frequencies by simply changing which resistive or capacitive elements are activated, thereby achieving frequency programmability without increasing overall device complexity.
2Reliability
If inductors are used in oscillator circuits to achieve stable frequency, then frequency stability is improved, but ease of manufacture deteriorates due to difficulty in fabricating inductors on integrated circuits
Solution Approach 1:
The patent substitutes the mechanical/physical inductor component with an electronic RC (resistor-capacitor) network that provides equivalent oscillatory behavior. This replacement eliminates the need for difficult-to-fabricate inductors on integrated circuits while maintaining the essential oscillation function, thereby improving ease of manufacture without sacrificing frequency stability.
Solution Approach 2:
The patent achieves frequency determination through RC time constants rather than inductive reactance, fundamentally changing the physical parameter basis of the oscillator from L (inductance) to RC (resistance-capacitance) products. This parameter substitution enables standard integrated circuit fabrication techniques to be used instead of specialized inductor fabrication processes.
3Adaptability or versatility
If variable capacitors are used with floating nodes that swing across supply and ground voltages, then frequency adjustment capability is improved, but reliability and noise performance worsen
Solution Approach 1:
The patent introduces an intermediary mechanism (switched capacitor network with controlled nodes) that mediates between the frequency adjustment requirement and the noise performance constraint. By using switches to connect capacitive elements to controlled voltage nodes rather than allowing direct floating swings, the circuit achieves frequency adjustability while maintaining better noise performance and reliability.
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 enables a programmable frequency RC oscillator with improved noise performance and flexibility, allowing for precise control of clock signals in digital logic circuits without the practical difficulties of variable resistors and capacitors, enhancing the utility of RC oscillators in integrated circuits.
Implementation Method 1
The delay element may have a resistance, R, and a capacitance, C, and the delay may be determined by an RC time constant of the delay element.
Data Source
AI summary
An oscillator circuit having a programmable output frequency may include a first delay section having a negative gain and a variable delay that is set by a control signal provided to the first delay section. A second delay section having a negative gain and a fixed delay may be connected in series with the first delay section. The oscillator circuit may include an output comprising the output of the second delay section having a frequency that is dependent on the delay of the first delay section and the delay of second delay section.