Offset-Cancelled Current Mirror Using Stored Voltage Calibration
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Solution Overview
Problem
Current current mirrors face challenges in accurately reproducing reference currents due to significant offset voltages, which are exacerbated by the smaller scale of transistors in advanced manufacturing technologies, affecting stability and yield in semiconductor production.
Innovation Solution
An offset cancellation current mirror circuit comprising multiple transistors, capacitors, and resistors, with specific switching configurations to generate and maintain a potential difference, calibrating the inaccuracy caused by smaller transistors and reducing the influence of current distinctions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transistor scale is reduced to improve manufacturing density, then manufacturing productivity is improved, but offset voltage increases causing current mirror accuracy to deteriorate
Solution Approach 1:
The patent applies preliminary action by measuring and storing the offset voltage in capacitors before the current mirror operation. The offset cancellation circuit measures the offset voltage between matched transistors and stores it in capacitors during a calibration phase, then uses this stored information to compensate for the offset during normal operation, thereby maintaining accuracy despite smaller transistor scales
Solution Approach 2:
The patent uses capacitors as intermediary elements to store offset voltage information and switches as mediators to control the calibration and operation phases. These intermediary components enable the system to separate the offset measurement function from the current mirroring function, allowing accurate current reproduction even with small transistors
2Productivity
If transistor scale is reduced to improve manufacturing density, then manufacturing productivity is improved, but current mirror stability deteriorates due to larger offset voltage
Solution Approach 1:
The calibration phase performs preliminary measurement and storage of offset voltage in capacitors before normal operation begins. This preliminary action ensures that stability-critical offset compensation is established before the current mirror enters its operational state, maintaining stability despite reduced transistor dimensions
Solution Approach 2:
The patent implements feedback by using the stored offset voltage information to continuously compensate for mismatches during current mirror operation. The circuit uses the pre-stored offset data to adjust and maintain stable current reproduction, creating a feedback mechanism that counteracts the destabilizing effect of small transistor offsets
3Manufacturing precision
If offset voltage is measured and stored in capacitors, then current mirror accuracy is improved, but device complexity increases due to additional components
Solution Approach 1:
The patent merges the offset cancellation functionality with the existing current mirror structure by integrating capacitors and switches into the conventional current mirror layout. The calibration and operation phases are merged into a single unified circuit that performs both functions sequentially, reducing the need for entirely separate offset cancellation circuits
Solution Approach 2:
The current mirror circuit is designed with multi-functionality to perform both normal current mirroring operation and offset calibration/compensation. The same transistors, capacitors, and switches serve dual purposes: current mirroring during operation and offset measurement/storage during calibration, thereby improving accuracy without proportionally increasing complexity
Data Source
AI summary
The present invention discloses an offset cancellation current mirror and method thereof. The offset cancellation current minor comprises a first current mirror, a second current minor, switches and resistors. The first current minor comprises two transistors and a capacitance, the capacitance is used to store an electrical potential difference when the switches are turned on in ways of connecting the first current mirror with the resistor. When the switches is turned off in ways of disconnecting the first current mirror with the resistor and connecting the first current mirror with the second current minor, the electrical potential difference stored in the capacitance is used to correct the difference of the two transistors due to manufacture process.