Trimmable Current Reference Generator for Process Variation Compensation
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Solution Overview
Problem
Current reference generators for semiconductor non-volatile memories lack stability with respect to manufacturing process variations, leading to deviations in reference current due to stochastic errors and process skews, resulting in inconsistent performance across different batches.
Innovation Solution
A trimmable current reference generator is designed with a control stage that adjusts the partition factor of the voltage reference generator and the aspect ratio of the active element to maintain a stable reference current, compensating for changes in threshold voltage and gain factor caused by process corners, using a bandgap voltage reference and a control signal to trim the aspect ratio and partition factor based on the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a bandgap voltage reference generator coupled to an active element is used to generate reference current, then temperature and power supply stability is improved, but manufacturing process variation sensitivity increases
Solution Approach 1:
The patent makes the reference current dynamic by introducing a control stage that adjusts the aspect ratio of the active element based on detected process corners. Instead of a fixed design, the system adapts its parameters (W/L ratio) according to the actual manufacturing process characteristics, allowing the reference current to remain stable across different process variations while maintaining temperature stability.
Solution Approach 2:
The patent changes the physical parameters of the active element (specifically the aspect ratio W/L) to compensate for process variations. By detecting the process corner and selecting appropriate trim values that modify the aspect ratio, the system adjusts key parameters to maintain reference current stability despite manufacturing deviations.
2Device complexity
If process corners are not compensated, then device complexity is reduced, but reference current stability deteriorates
Solution Approach 1:
The patent segments the reference current generation into multiple independent paths, each optimized for a specific process corner (fast, slow, typical). The control stage selects the appropriate segment based on the detected process corner, allowing the system to maintain high reliability without requiring a single complex circuit that tries to handle all variations simultaneously.
Solution Approach 2:
The system performs self-characterization by automatically detecting its own process corner through test current measurements and then self-adjusting by selecting the appropriate aspect ratio trim value. This self-service approach eliminates the need for external calibration or complex manual adjustment procedures.
3Reliability
If trimmable parameters are added to compensate for process skews, then reference current stability improves, but device complexity increases
Solution Approach 1:
The patent performs preliminary characterization during manufacturing by measuring test currents and determining the process corner before the device is shipped. This preliminary action allows the system to pre-select the appropriate trim values, so that during normal operation, only simple switching between pre-determined configurations is needed, rather than requiring complex real-time adjustment mechanisms.
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
The solution ensures a stable and constant reference current irrespective of temperature and power supply variations, effectively compensating for process skews and maintaining desired current values across different manufacturing processes, thereby enhancing the repeatability of memory operations.
Implementation Method 1
bandgap voltage references create a very stable reference voltage with respect to both temperature and power supply variations
Implementation Method 2
control, based on the control signal CS (in turn based on the process corner), to compensate for process skews
Data Source
AI summary
In a current reference generator device, a voltage reference generator stage generates a reference voltage (Vref) and an active element output stage receives the reference voltage (Vref) and outputs a reference current (Iref) as a function of the reference voltage (Vref). A control stage is operatively coupled to the voltage reference generator stage and to the active element output stage and controls a first trimmable parameter (m) associated to the voltage reference generator stage and a second trimmable parameter associated to the active element output stage, so as to compensate for changes in a value of the reference current (Iref) due to manufacturing process deviations.