RC Oscillator Inverter Chain With Supply-Compensated Delay

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Solution Overview

Problem

Existing oscillator circuits, such as crystal, LC, RC, and ring oscillators, face challenges in stability, size, power consumption, and frequency variation due to manufacturing processes, supply voltage, and temperature variations, with crystal oscillators requiring external components and LC oscillators needing significant area and high current.

Innovation Solution

An RC oscillator with a resistor, capacitor, and signal propagating inverters generates a time-varying voltage, where the supply voltage is adjusted to maintain a constant time delay, ensuring frequency stability and reducing size and power consumption by using a self-biased inverter design that matches the sensitivity of other inverters, thus minimizing variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If crystal oscillators are used to achieve high frequency stability, then frequency variation is reduced to below 100 ppm, but external crystal components are required which increase board space and device cost

Engineering Contradiction:

Improvefrequency stabilityVSAvoidboard space

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The invention extracts the oscillation function from external crystal components and implements it entirely within the IC chip using integrated RC circuits and inverters, eliminating the need for external crystals while maintaining acceptable frequency stability through internal compensation mechanisms

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent uses multiple copies of the same inverter circuit stage in series, where each stage is designed to have matched characteristics. This copying approach allows the oscillation frequency to be determined by the RC time constant rather than by variations in individual inverter characteristics, achieving stability without external crystals

Inventive Principle:

Principle #26Copying

2Speed

If LC oscillators are used to achieve high frequency operation, then frequency stability is improved, but large inductor area and high current consumption are required

Engineering Contradiction:

Improveoperating frequencyVSAvoidinductor area

Core Design Contradiction:

SpeedVSArea of stationary object

Solution Approach 1:

The invention replaces the mechanical inductor component with an equivalent RC circuit implementation. The oscillation is achieved through the interaction of resistive and capacitive elements with inverters, eliminating the need for physical inductors and their associated area requirements while maintaining high-frequency operation capability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operating parameters by using multiple smaller capacitor stages in series rather than a single large inductor. The total capacitance is distributed across multiple stages, each with smaller individual capacitor values, allowing high-frequency operation with reduced area and lower current consumption

Inventive Principle:

Principle #35Parameter changes

3Area of stationary object

If RC oscillators are used to reduce area and power consumption, then device size and power usage are reduced, but frequency variation increases due to manufacturing and environmental factors

Engineering Contradiction:

Improvechip areaVSAvoidfrequency stability

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The invention segments the oscillation circuit into multiple identical inverter stages, each with its own RC network. This segmentation allows the frequency-determining RC time constant to be less sensitive to variations in individual components, as the overall frequency is determined by the sum of multiple matched stages rather than by single critical components

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses homogeneous, matched inverter circuits throughout the oscillation path. All inverters are designed with identical characteristics and are fabricated using the same process, ensuring that variations in manufacturing, temperature, and supply voltage affect all stages equally and thus cancel out in determining the overall oscillation frequency

Inventive Principle:

Principle #33Homogeneity

4Reliability

If supply voltage is adjusted to maintain constant time delay, then frequency stability is improved, but circuit complexity increases

Engineering Contradiction:

Improvefrequency stabilityVSAvoidvoltage adjustment circuitry

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention implements a self-biasing inverter circuit that automatically adjusts its operating point based on the supply voltage. The inverter's biasing network self-regulates to maintain the correct time delay through the RC network, eliminating the need for external voltage adjustment circuitry while maintaining frequency stability across varying supply conditions

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS9300247B2RC oscillator with additional inverter in series with capacitor

Publication Date: 2016.03.29 TEXAS INSTRUMENTS INC

AI summary

In an electronic device, an RC oscillator generally includes a resistor, a capacitor and at least one inverter. The resistor and capacitor generate a time-varying voltage. The time-varying voltage is provided to the at least one inverter to cause a clock signal to propagate therethrough. The clock signal propagates with a time delay that is at least partially dependent on a supply voltage. The supply voltage is adjusted to maintain the time delay at almost a constant value.