Reference Current Source Temperature Control via Subthreshold Transistors
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Solution Overview
Problem
Conventional reference current sources in semiconductor integrated circuits face challenges in temperature-dependent variations and power supply voltage independence, making it difficult to adjust the temperature characteristic of the reference current effectively.
Innovation Solution
A reference current source design that includes a first and second transistor with control terminals coupled, a current mirror circuit, and additional transistors configured to operate in a subthreshold region, allowing for control of the temperature characteristic by adjusting the sizes and mirror ratio of transistors on a third path, which includes a resistance between the source of a fourth transistor and one end of the second transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional reference current source design is used, then the reference current is independent of power supply voltage, but the temperature characteristic cannot be adjusted effectively
Solution Approach 1:
The reference current source is divided into multiple independent paths (first path with second transistor, second path with first transistor, third path with third and fourth transistors). Each path can be independently configured with different transistor sizes and mirror ratios, allowing separate optimization for temperature compensation without affecting power supply independence.
Solution Approach 2:
Different paths are assigned different functions: the first and second paths maintain power supply independence, while the third path with subthreshold transistors is specifically designed for temperature characteristic adjustment. The local quality of each path is optimized for its specific purpose.
2Reliability
If resistance value is increased to reduce current variation, then current stability improves, but element area increases
Solution Approach 1:
The invention changes the operating parameter of transistors from saturation region to subthreshold region. Subthreshold transistors exhibit exponential current-voltage characteristics that are less sensitive to process variations and temperature, reducing current variation without requiring large resistance values.
Solution Approach 2:
The current mirror circuit copies the reference current from the first path to the second and third paths with different mirror ratios. This allows the same small resistance to be used multiple times to generate different current levels, reducing the need for large resistance values.
Data Source
AI summary
A first transistor and a second transistor have control terminals coupled to each other. A current mirror circuit supplies a current having the same amount as that of a current Iref flowing through a first path including the second transistor to a second path including the first transistor and supplies a current having a predetermined number of times m of a current amount of the current Iref of the first path to a third path separate from the second path. The third transistor and a fourth transistor are provided on the third path. The third transistor has a source coupled to one end of the first transistor, and the fourth transistor has a gate coupled to a gate of the third transistor. A resistor is provided between a source of the fourth transistor and one end of the second transistor.