Self-Biasing Integrated Oscillator Without External Reference
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Solution Overview
Problem
Existing oscillators in integrated circuits face challenges with high costs due to the use of crystal or ceramic resonators, and relaxation oscillators operate at low frequencies with precision components that vary significantly in standard integrated circuit processing, requiring external components that add cost and circuit board area.
Innovation Solution
An integrated oscillator design utilizing an R-S flipflop, current-source transistor, and current-steering transistors with capacitors, along with a feedback circuit to sense voltages and adjust the oscillator frequency, allowing for internal frequency generation without external precision components, thus reducing costs and increasing frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If crystal or ceramic resonator oscillators are used, then frequency stability and reliability are improved, but system cost increases
Solution Approach 1:
The patent replaces expensive crystal or ceramic resonators with a low-cost integrated relaxation oscillator circuit that uses standard semiconductor fabrication processes. The oscillator uses readily available transistors, capacitors, and resistors that can be manufactured using conventional CMOS or bipolar processes, eliminating the need for expensive external resonator components while maintaining acceptable frequency stability for the application.
Solution Approach 2:
The patent substitutes the mechanical resonance system (crystal or ceramic resonator) with an electronic relaxation oscillator system. Instead of relying on mechanical vibrations at resonant frequencies, the invention uses electronic components (transistors, capacitors, resistors) to generate oscillations through charging and discharging cycles, thereby eliminating the need for mechanical resonating structures and reducing system cost.
2Manufacturing precision
If external precision resistors and capacitors are used in relaxation oscillators, then frequency precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent combines multiple functions into integrated on-chip components. The bias circuit generates reference voltages that are used by both the oscillator circuit and the feedback system. The feedback network integrates temperature compensation and frequency control functions within the same chip, eliminating the need for separate external precision components. This merging reduces component count and simplifies manufacturing while maintaining frequency precision.
Solution Approach 2:
The oscillator circuit includes an automatic bias generation system that creates stable reference voltages from the power supply itself, without requiring external precision voltage references. The feedback network automatically adjusts operating parameters based on temperature and process variations, enabling the circuit to self-correct and maintain frequency precision without external intervention or additional precision components.
3Reliability
If external precision resistors and capacitors are used, then oscillator frequency stability is improved, but circuit board area and pin count increase
Solution Approach 1:
The patent integrates the oscillator, bias circuit, and feedback network into a single monolithic integrated circuit chip. All frequency-determining components (capacitors, resistors, transistors) are fabricated on the same semiconductor substrate using standard processes. This consolidation eliminates the need for multiple discrete external components, thereby reducing circuit board area and the number of required connection pins while maintaining frequency stability through on-chip integration.
4Ease of manufacture
If standard integrated circuit processing is used for resistors and capacitors, then manufacturing cost is reduced, but component precision deteriorates
Solution Approach 1:
The patent employs a feedback mechanism that dynamically adjusts operating parameters to compensate for variations in resistor and capacitor values caused by standard fabrication processes. The bias circuit generates reference voltages that are sensitive to these parameter variations, and the feedback network automatically adjusts the oscillator operating point to maintain stable frequency. This allows the use of low-precision standard components while achieving high frequency stability through parameter compensation.
Solution Approach 2:
The oscillator includes a feedback network that continuously monitors the oscillation frequency and adjusts the bias conditions to compensate for component variations. The feedback signal is derived from the oscillator output and is used to control the bias voltages, creating a closed-loop system that automatically corrects for deviations caused by process variations in resistors and capacitors. This feedback mechanism enables the use of standard-tolerance components while maintaining precise frequency control.
Data Source
AI summary
An integrated oscillator has an R-S flipflop; a first and second capacitor; a current source transistor; first and second current-steering transistors, each having a source coupled to the current source transistor, with drains coupled to the first and second capacitor respectively. The first current-steering transistor has gate coupled to a first output of the R-S flipflop, and the second current-steering transistor has gate coupled to a second output of the R-S flipflop. The oscillator has a first sense inverter having input from the first capacitor and powered by a feedback circuit adapted to sense voltages on the first and second capacitor; and a second sense inverter having input from the second capacitor and powered by the feedback circuit. The R-S flipflop has a first input coupled to an output of the first sense inverter and a second input coupled to an output of the second sense inverter.