Cascode Device With Common Body And Multiple Source Regions
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Solution Overview
Problem
Current digitally controlled current source circuits with high-voltage tolerant outputs require large cascode devices, which occupy significant area on semiconductor dies, and combining currents into a shared cascode device compromises linearity.
Innovation Solution
A cascode device with a field effect transistor having a common body region and multiple source regions, each separated by the body region, and a shared drain region, allowing for a compact design without compromising linearity, along with digital control circuitry to enable/disable current sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate scaled cascode devices are used for each current source element, then linearity is maintained, but area occupied on semiconductor die increases significantly
Solution Approach 1:
The patent combines multiple current source elements into a single cascode device structure with a shared common body region and common drain region. Multiple source regions are integrated within the common body region, allowing currents from separate current sources to be combined before being input into the shared cascode device, thereby reducing the total area occupied on the semiconductor die while maintaining circuit functionality
Solution Approach 2:
The common body region is segmented to accommodate multiple source regions, each separated from others by the common body region. This segmentation allows individual current source elements to be independently controlled while sharing the common cascode structure, enabling area reduction without completely sacrificing the ability to maintain linearity through proper design
2Area of stationary object
If currents from separate current sources are combined into a shared cascode device, then area occupied is reduced, but linearity is compromised
Solution Approach 1:
The patent applies local quality by providing individually sized source regions within the common body region, where each source region can be optimized for its specific current source element. This allows the cascode device to handle different current levels from different sources while maintaining proper linearity characteristics for each channel, thus preserving linearity while achieving area reduction through the shared structure
Data Source
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AI summary
A circuit comprising a cascode device comprising a field effect transistor. The field effect transistor includes a common body region. The field effect transistor also includes a plurality of source regions. The source regions form inputs of the cascode device. Each source region of the plurality of source regions is separated from each other source region of the plurality of source regions by the common body region. The field effect transistor further includes a common gate. The field effect transistor also includes a common drain region. The common drain region forms an output of the cascode device. The circuit may further include a plurality of groups of one or more current sources each group coupled to a respective one of the inputs of the cascode device, and a current output coupled to the output of the cascode device. A method of operating a current source circuit.