Bias Circuit for Low-Threshold Current Mirror Saturation
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Solution Overview
Problem
Low threshold voltage transistors face challenges in maintaining saturation mode operation over a wide temperature range due to changing threshold voltage polarity, making them unsuitable for use in current mirrors and other circuits that require reduced power supply voltages.
Innovation Solution
A bias circuit is introduced, comprising a resistor and bias transistors, which biases the low threshold voltage transistors to maintain saturation mode operation by adjusting the drain-source voltage with a Vshift voltage, ensuring operation even when the threshold voltage is negative, thereby stabilizing current mirror performance across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If low threshold voltage transistors are used to reduce power supply voltage, then power consumption is reduced, but saturation mode operation cannot be maintained over wide temperature range
Solution Approach 1:
A bias circuit is introduced as an intermediary component between the power supply and the low threshold voltage transistor. This bias circuit generates a adjusted supply voltage that compensates for threshold voltage variations over temperature, allowing the transistor to maintain saturation mode operation while still benefiting from low power consumption.
Solution Approach 2:
The bias circuit dynamically adjusts the supply voltage parameter based on temperature conditions. When the threshold voltage becomes negative at high temperatures, the bias circuit modifies the supply voltage to ensure the transistor operates in saturation mode, thereby maintaining reliable operation across the full temperature range.
2Power
If low threshold voltage transistors are used for reduced power supply voltage, then circuit operation at lower voltages is enabled, but current mirroring accuracy deteriorates due to inability to maintain saturation mode
Solution Approach 1:
The bias circuit serves as a mediator that conditions the supply voltage before it reaches the current mirror transistors. By adjusting the supply voltage to account for threshold voltage shifts, the bias circuit ensures that current mirror transistors remain in saturation mode, thereby preserving current mirroring accuracy even when using low threshold voltage transistors for reduced power supply voltage.
3Reliability
If standard threshold voltage transistors are used, then saturation mode operation is maintained, but power consumption increases due to higher power supply voltage requirement
Solution Approach 1:
Instead of using standard threshold voltage transistors that require higher supply voltages, the invention changes the supply voltage parameter dynamically through the bias circuit. This allows low threshold voltage transistors to operate in saturation mode at lower supply voltages by compensating for threshold voltage variations, thereby reducing power consumption while maintaining reliable saturation mode operation.
Data Source
AI summary
A current mirror circuit includes a first current mirror transistor, a second current mirror transistor, and a bias circuit. The first current mirror transistor includes a gate and a drain. The second current mirror transistor includes a gate coupled to the gate of the first current mirror transistor. The first current mirror transistor and the second current mirror transistor are low threshold voltage transistors. The bias circuit is coupled to the gate and the drain of the first current mirror transistor. The bias circuit is configured to bias the first current mirror transistor to operate in a saturation mode when a threshold voltage of the first current mirror transistor is a negative voltage.