Ring Oscillator Circuit for Transistor Variation Outlier Measurement
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Solution Overview
Problem
Current measurement techniques for transistor 'on-current' and 'off-current' in integrated circuits are slow and imprecise, failing to isolate variation effects in individual transistors and requiring significant time and area for analog components, which masks potential outliers.
Innovation Solution
The integrated circuit employs a plurality of ring oscillator macro circuits with multiplexers and divide-by-two circuits to measure frequency variations, allowing for simultaneous measurement of multiple devices and on-chip frequency measurement to derive threshold voltage variations, while using dynamic and static latches to measure leakage without analog noise issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If known measurement techniques are used for transistor on-current, then measurement can be performed, but measurement time increases and isolation of variation effects is lost
Solution Approach 1:
The patent divides the measurement system into multiple independent ring oscillator macro circuits, each containing separate test devices that can be measured independently. This segmentation allows simultaneous measurement of multiple devices while maintaining isolation of variation effects, resolving the contradiction between measurement precision and time loss.
Solution Approach 2:
The patent replaces traditional analog measurement techniques with digital ring oscillator-based measurement. By substituting analog current measurements with digital frequency measurements, the system achieves faster measurement speed while maintaining the ability to isolate variation effects through the digital domain's inherent isolation properties.
2Measurement precision
If analog measurement techniques are used for transistor off-current, then leakage measurement can be performed, but measurement time increases and area increases
Solution Approach 1:
The patent replaces analog leakage measurement techniques with digital ring oscillator-based measurement. The ring oscillators convert small leakage currents into measurable frequency shifts, enabling precise leakage measurement without the time-consuming capacitor charging process required by analog techniques. This substitution dramatically reduces measurement time while maintaining precision.
Solution Approach 2:
The patent changes the measurement parameter from direct current measurement to frequency measurement. By measuring the frequency of ring oscillators that are sensitive to leakage currents, the system achieves precise leakage measurement without requiring large capacitors or long integration times, thus resolving the contradiction between measurement precision and time loss.
3Measurement precision
If analog components are increased in size for leakage measurement, then noise and offsets decrease, but area increases
Solution Approach 1:
The patent replaces large analog components (capacitors and opamps) with compact digital ring oscillator circuits. The ring oscillators achieve high sensitivity to leakage currents through their oscillation frequency, which is inherently sensitive to small current changes. This substitution eliminates the need for large analog components while maintaining measurement precision and reducing noise.
Solution Approach 2:
The patent changes the measurement approach from direct voltage comparison to frequency measurement. The ring oscillator's frequency serves as the measurement parameter, and this frequency is highly sensitive to leakage currents. This parameter change allows precise measurement without requiring large analog components, thus resolving the contradiction between measurement precision and area.
4Area of stationary object
If multiple test devices are lumped into a single measurement circuit, then area decreases, but isolation of variation effects is lost
Solution Approach 1:
The patent segments the measurement circuit into multiple independent ring oscillator macro circuits, each capable of measuring individual test devices. This segmentation maintains the ability to isolate variation effects while keeping the overall area compact through systematic arrangement and sharing of common infrastructure elements.
Solution Approach 2:
The patent designs the ring oscillator macro circuits with universal structures that can measure multiple types of transistor parameters (on-current, off-current, threshold voltage). Each macro circuit serves multiple measurement functions, reducing the need for separate dedicated circuits for each parameter, thus minimizing total area while maintaining measurement isolation.
Data Source
AI summary
Embodiments of the invention provide for integrated circuits for testing one or more transistors for process variation effects. According to an embodiment, the integrated circuit can include: a plurality of ring oscillator macro circuits, wherein each ring oscillator macro circuit includes two ring oscillators, a first multiplexer, and a first divide-by-two circuit; a multiplexer stage; a divide-by-two circuit stage; a second multiplexer; a second divide-by-two circuit; and frequency measurement circuit. According to another embodiment, the integrated circuit can include: a first shift register including a plurality of devices-under-test; a second shift register including a plurality of static latches; a first multiplexer configured to receive outputs from each of the plurality of DUTs; a second multiplexer configured to receive outputs from each of the plurality of static latches; and a comparator configured to compare an output from the first multiplexer with an output from the second multiplexer.