Memory Ring Oscillator Circuit for PVT-Stable Timing
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Solution Overview
Problem
On-chip ring-oscillators (ROs) in memory devices face challenges due to frequency control tolerance and variations in process corners, voltage biases, and temperature, leading to instability and timing errors, especially in applications requiring precise timing.
Innovation Solution
A circuit configuration using transistors connected in a loop, biased by a current source proportional to their threshold voltage, generates oscillating signals that are insensitive to process, voltage, and temperature variations, replacing off-chip crystal oscillators and on-chip phase-locked loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If off-chip crystal oscillators and on-chip phase-locked loops are used for frequency control, then frequency accuracy can be maintained, but device complexity and area increase
Solution Approach 1:
The patent extracts the frequency control function from complex off-chip crystal oscillators and on-chip phase-locked loops, implementing it instead through a simplified ring oscillator circuit with specific transistor configurations that inherently provide PVT compensation, thereby reducing device complexity while maintaining frequency accuracy
Solution Approach 2:
The patent creates a simplified copy of the frequency control function using ring oscillator circuits that replicate the essential oscillation behavior without requiring the complex supporting infrastructure of crystal oscillators or phase-locked loops, achieving comparable frequency accuracy with reduced complexity
2Area of stationary object
If traditional ring-oscillators are used in memory devices, then area efficiency improves, but timing precision deteriorates due to PVT variations
Solution Approach 1:
The patent changes the operating parameters of the ring oscillator by biasing transistors at specific current levels and configuring transistor ratios to compensate for PVT variations, thereby maintaining timing precision while preserving the area efficiency benefits of on-chip oscillation
Solution Approach 2:
The patent implements self-compensating mechanisms within the ring oscillator circuit where transistor configurations automatically adjust for PVT variations without requiring external calibration or control circuits, maintaining timing precision through self-service compensation
3Stability of the object's composition
If frequency control circuits are made more complex to achieve PVT independence, then stability improves, but power consumption increases
Solution Approach 1:
The patent implements self-compensating mechanisms within the ring oscillator circuit where transistor configurations automatically adjust for PVT variations without requiring external calibration or control circuits, maintaining timing precision through self-service compensation
Data Source
AI summary
A circuit includes a current source configured to provide a reference current and a plurality of transistors each configured to receive the reference current from the current source. Each of the plurality of transistors has a same conductive type and includes a first source/drain terminal connected to a gate terminal of a first neighboring one of the transistors, a second source/drain terminal connected to ground, and a gate terminal connected to a source/drain terminal of a second neighboring one of the transistors.