Stacked Cascode Current Mirror for High Impedance at Low Voltage
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Solution Overview
Problem
Current transistor current sources face challenges in maintaining high output impedance at low operating voltages, leading to reduced operating voltage ranges and increased complexity, noise, and power consumption when using cascode structures or level shifters.
Innovation Solution
A stacked cascode current source configuration with equal transistor stacks creates common gate nodes, allowing for high output impedance and extended operating voltage range without removing output devices, using a configuration where the second transistor stack mirrors the current of the first stack, maintaining high impedance across a wider voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If transistors are made smaller and operating voltages are reduced, then power consumption is reduced, but output impedance decreases due to increased sensitivity of MOSFET current to drain voltage
Solution Approach 1:
The current source circuit is divided into multiple transistor stages (first current source with first transistor, second current source with second transistor) connected in a specific configuration. This segmentation allows each transistor to operate independently within its optimal voltage range, maintaining high output impedance even when overall operating voltage is reduced.
Solution Approach 2:
The patent introduces a new dimensional approach by stacking transistors in series to create multiple voltage nodes (first voltage node, second voltage node) between source and drain. This multi-dimensional voltage distribution allows the circuit to maintain proper transistor biasing and high output impedance across a wider range of operating voltages.
2Reliability
If cascode current source is used to achieve high output impedance, then output impedance is improved, but operating voltage range is reduced due to voltage requirements across stacked transistors
Solution Approach 1:
The circuit dynamically adapts to different voltage conditions by utilizing two separate current sources that can operate independently. The first current source operates with voltage V1 across its transistor, and the second current source operates with voltage V2 across its transistor, allowing the overall circuit to adapt to a wider range of supply voltages while maintaining high output impedance.
Solution Approach 2:
The patent changes the voltage parameters by introducing separate voltage controls for each transistor stage. Instead of requiring a single high voltage across the entire cascode structure, the circuit allows independent voltage distribution (V1 and V2) across each transistor, expanding the adaptable voltage range while preserving the high impedance characteristic.
3Adaptability or versatility
If level shifters and feedback circuitry are added to extend operating voltage range, then operating voltage range is improved, but device complexity and noise increase
Solution Approach 1:
The circuit achieves voltage range extension through self-service by using the transistors' own gate-source voltage characteristics to provide the necessary level shifting. The gate terminals are connected to appropriate voltage nodes, allowing each transistor to automatically establish its operating point without external level shifter circuits.
Data Source
AI summary
Apparatus are provided for a stacked cascode current source. An apparatus is provided for an electrical device comprising an input node and an output node. A first transistor stack is coupled to the input node. The first transistor stack includes a first transistor and a second transistor. A drain terminal and a gate terminal of the first transistor are coupled to the input node. A drain terminal of the second transistor is coupled to a source terminal of the first transistor and a gate terminal of the second transistor is coupled to the input node. A second transistor stack coupled to the first transistor stack and the output node to create a current mirror for the first transistor stack.