Current Mirror DAC Circuit for Low-Voltage Accuracy
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Solution Overview
Problem
Current digital-to-analog converters face issues with current accuracy due to the Early effect and voltage drops across transistors, leading to degradation in mirror ratio accuracy and increased voltage requirements.
Innovation Solution
A digital-to-analog converter design incorporating a current mirror circuit with cascade-coupled transistors and analog switches controlled by digital signals, which reduces voltage drops and stabilizes drain potentials, thereby improving current accuracy and allowing for low-voltage operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cascade current mirrors are used to reduce current errors due to drain voltage variations, then current accuracy is improved, but voltage drops across transistors increase
Solution Approach 1:
The patent divides the current mirror circuit into multiple stages with intermediate buffer circuits. Each stage handles a portion of the current mirroring function, allowing voltage drops to be distributed and managed at each stage rather than accumulating in a single cascade structure. This segmentation maintains current accuracy while controlling overall voltage drop.
Solution Approach 2:
The patent introduces buffer circuits as intermediary elements between the current mirror stages. These buffer circuits act as mediators that isolate the voltage drops of different stages, preventing them from directly affecting each other. The buffers maintain stable drain potentials for the mirror transistors while allowing the overall circuit to operate at lower voltages.
2Measurement precision
If more transistors are added to the cascade current mirror circuit to stabilize drain potentials, then current accuracy is improved, but device complexity increases
Solution Approach 1:
The patent designs the buffer circuits to serve multiple functions simultaneously: they stabilize drain potentials for current accuracy, act as isolation elements between stages, and enable low-voltage operation. This multi-functionality reduces the need for additional dedicated components, thereby controlling circuit complexity while maintaining high current accuracy.
3Productivity
If conventional current mirror circuits are used, then current copying function is achieved, but voltage drops lead to Early effect and degradation of mirror ratio accuracy
Solution Approach 1:
The patent ensures continuous stabilization of drain potentials throughout the current mirror operation by using buffer circuits that actively maintain constant voltage levels. This continuous voltage stabilization prevents the drain potential variations that cause Early effect, thereby maintaining high mirror ratio accuracy throughout the current copying process without interruption or degradation.
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 proposed design achieves stable and accurate current output at lower voltages, reducing voltage drops and maintaining current accuracy, particularly beneficial for low-voltage applications.
Implementation Method 1
a mirror circuit including a first transistor to copy a reference current at a predetermined mirror ratio, and a second transistor cascade coupled with the first transistor
Implementation Method 2
an analog switch coupled with a gate of the second transistor, the analog switch being configured to be controlled, by a digital signal input from outside, so as to be turned on or off
Implementation Method 3
which reduces voltage drops and stabilizes drain potentials, thereby improving current accuracy and allowing for low-voltage operation
Data Source
AI summary
There is provided a digital-to-analog converter including: a mirror circuit including a first transistor to copy a reference current at a predetermined mirror ratio, and a second transistor cascade coupled with the first transistor; and an analog switch coupled with a gate of the second transistor, the analog switch being configured to be controlled, by a digital signal input from outside, so as to be turned on or off.