Cascoded Power Switch Topology for SOA-Safe High-Voltage Operation
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Solution Overview
Problem
Low voltage integrated circuit devices used in high voltage applications are prone to Safe Operating Area (SOA) violations, leading to potential device damage, and suffer from significant leakage currents, complicating low power design.
Innovation Solution
The design of cascoded transistor switches using low voltage NMOS and PMOS devices, connected in series to extend operating voltage and reduce leakage currents, with a configuration that includes multiple switch transistors, analog multiplexers, and voltage selectors to manage voltage levels effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low voltage devices are used in high voltage applications, then device compatibility and ease of manufacture are improved, but Safe Operating Area violations occur leading to device damage
Solution Approach 1:
The power switch is segmented into multiple cascoded transistors (first transistor, second transistor, third transistor) connected in series. Each transistor handles a portion of the total voltage, allowing low voltage devices to operate safely in high voltage environments without exceeding their individual SOA limits.
Solution Approach 2:
The body terminals of the cascoded transistors serve as intermediaries to distribute and control voltage levels. By tying each transistor's source to its body, the structure creates intermediate voltage nodes that prevent any single device from experiencing excessive voltage stress.
2Ease of manufacture
If low voltage devices are used in high voltage applications, then device compatibility is improved, but leakage currents increase making low power design difficult
Solution Approach 1:
The segmentation into cascoded transistors distributes the voltage stress across multiple devices, which reduces the leakage current in each individual transistor. The series connection ensures that the same current flows through all transistors, and each operates within its optimal voltage range, minimizing total leakage.
Solution Approach 2:
The invention changes the voltage parameters across each transistor by using cascoding architecture. Each transistor experiences a fraction of the total voltage rather than the full high voltage, which significantly reduces leakage currents and enables low power design while maintaining compatibility with low voltage devices.
3Reliability
If cascoded transistors are used to extend operating voltage, then voltage handling capability is improved, but device complexity increases
Solution Approach 1:
The power switch is divided into three cascoded transistors connected in series, where each transistor handles a portion of the total voltage. This segmentation allows the use of standard low voltage devices while achieving high voltage capability, with the complexity distributed across multiple simple, identical units rather than one complex device.
Solution Approach 2:
By changing the voltage distribution parameters through cascoding, the invention achieves high voltage handling capability using standard low voltage transistors. The parameter change approach (dividing voltage across multiple devices) simplifies device selection and manufacturing while maintaining reliability.
Data Source
AI summary
A power switch includes a first transistor having a first current electrode corresponding to an output of the switch, a second transistor having a first current electrode coupled to a second current electrode of the first transistor, and a third transistor having a first current electrode coupled to a second current electrode of the second transistor and a second current electrode coupled to a first power supply voltage terminal which provides a first power supply voltage. The second current electrodes of each of the first, second, and third transistors are body-tied. An analog switch is either couples the second current electrode of the second transistor or a first reference voltage to a control electrode of the second transistor based on a control signal. A voltage selector circuit either couples the second current electrode of the first transistor or the first reference voltage to a control electrode of the first transistor.