Constant Current Circuit Using Segmented NMOS for High Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing constant current circuits for high voltage applications have high manufacturing costs due to the need for high breakdown-voltage NMOS transistors with different threshold voltages, which are costly to produce.
Innovation Solution
A constant current circuit design that includes a high breakdown-voltage depletion type NMOS transistor and a low breakdown-voltage depletion type NMOS transistor connected in series, where the gate of the high breakdown-voltage transistor is connected to the connecting point of the low breakdown-voltage transistors, allowing for reduced restrictive conditions on threshold voltage and lower manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high breakdown-voltage NMOS transistors with different threshold voltages are used, then the constant current circuit can operate in high voltage circuits, but the manufacturing cost increases
Solution Approach 1:
The low breakdown-voltage NMOS transistor is divided into two series-connected transistors (first and second depletion type NMOS transistors). This segmentation allows the gate of the high breakdown-voltage transistor to be connected to the intermediate node between them, enabling the high gate voltage needed for saturation operation without requiring a specially fabricated high threshold-voltage transistor, thus reducing manufacturing cost while maintaining current stability.
Solution Approach 2:
The invention changes the voltage parameter at the gate of the high breakdown-voltage NMOS transistor by connecting it to the connecting point of the two low breakdown-voltage transistors. This parameter change enables the high breakdown-voltage transistor to operate in saturation region even with standard threshold voltage, achieving stable constant current output without requiring expensive custom-transistor fabrication processes.
2Ease of manufacture
If the threshold voltage of the high breakdown-voltage NMOS transistor is restricted, then manufacturing cost is reduced, but the transistor may not operate in saturation
Solution Approach 1:
Instead of trying to achieve high gate voltage through a single transistor, the invention uses a series connection of two low breakdown-voltage transistors to create an intermediate voltage node. This dimensional change in the circuit topology allows the gate of the high breakdown-voltage transistor to receive the necessary high voltage without requiring the transistor itself to have special threshold voltage characteristics, enabling saturation operation with standard transistors.
Data Source
AI summary
There is provided a constant current circuit having a current characteristic satisfactory in a high voltage circuit while being low in manufacturing cost. The constant current circuit includes a high breakdown-voltage depletion type NMOS transistor and a low breakdown-voltage depletion type NMOS transistor connected in series between a first terminal and a second terminal. The low breakdown-voltage depletion type NMOS transistor includes a first depletion type NMOS transistor and a second depletion type NMOS transistor connected in series. The high breakdown-voltage depletion type NMOS transistor has a gate connected to a connecting point of the first depletion type NMOS transistor and the second depletion type NMOS transistor.