Current Steering DAC Switch With Threshold Control for Wider Output Swing
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Solution Overview
Problem
Conventional current switch circuits for D/A converters face challenges in achieving a wide output voltage range while maintaining low power consumption and chip area efficiency, especially under low power voltage conditions, and are sensitive to threshold voltage variations due to production processes.
Innovation Solution
A current switch circuit with a threshold voltage control circuit that adjusts the substrate voltage of transistors in the differential switch to achieve a higher threshold voltage, allowing for a wider output voltage range without increasing power consumption or chip area, and maintaining stability against threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If low voltage withstanding transistors are used to reduce power voltage, then power consumption is reduced, but output voltage range is limited
Solution Approach 1:
The patent changes the threshold voltage parameter of the differential switch transistors to a higher value (e.g., 0.5V or more) while maintaining low power voltage operation. This is achieved by using transistors with higher threshold voltage characteristics in the differential switch portion, allowing the output voltage range to extend to at least the threshold voltage value, thereby resolving the contradiction between low power consumption and sufficient output voltage range.
2Length of moving object
If threshold voltage of differential switch transistors is increased to widen output voltage range, then output voltage range is improved, but sensitivity to production process variations increases
Solution Approach 1:
The patent applies different transistor characteristics to different portions of the circuit. The differential switch transistors are specifically designed with higher threshold voltage characteristics, while other transistors in the circuit may use standard characteristics. This localized differentiation allows the output voltage range to be determined by the higher threshold voltage without requiring all transistors to have matched high threshold voltage, thereby reducing sensitivity to production process variations.
3Device complexity
If conventional current switch circuit is used, then circuit simplicity is maintained, but output voltage range is insufficient under low power voltage
Solution Approach 1:
The patent maintains the simple current switch circuit structure but changes the threshold voltage parameter of the differential switch transistors to a higher value. This parameter change allows the output voltage range to be extended to at least the threshold voltage value (0.5V or more) without adding complex circuitry, thereby resolving the contradiction between circuit simplicity and sufficient output voltage range.
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 enables a wider output voltage range without deteriorating circuit properties, reduces chip area and power consumption, and maintains a constant output voltage range despite production process variations, effectively addressing the limitations of conventional designs.
Implementation Method 1
a threshold voltage control circuit for outputting a substrate voltage to a substrate terminal of each of the first and second transistors to adjust a threshold voltage of the first and second transistors
Data Source
AI summary
In a current switch circuit A used for a current steering D/A converter, a current switch basic circuit 1 includes first and second transistors Tr121 and Tr122 included in a differential switch 12. A threshold voltage control circuit 5 has an output terminal Vbout controlling the substrate voltage to be outputted to the substrate terminal of each of the two transistors Tr121 and Tr122 included in the differential switch 12 for controlling the threshold voltage of the two transistors of the differential switch. Accordingly, the present invention improves the decrease in the dynamic range of the current switch basic circuit 1 dependent on the threshold of each of the two transistors in the differential switch 12 and realizes a wider output voltage range without causing deterioration in properties even in a case that the power voltage is reduced in the current switch basic circuit 1.