PMOS Bulk Switching Circuit With Voltage Isolation for Latch-Up Prevention

The patent divides the bulk voltage switching circuit into multiple PMOS transistors (first PMOS transistor, second PMOS transistor, third PMOS transistor) with different threshold voltages, where each transistor handles a specific voltage range. This segmentation allows the circuit to achieve fine-grained voltage difference resolution while maintaining reliability, as each transistor operates in its optimal voltage range.

The patent utilizes PMOS transistors with different threshold voltages (VTH1, VTH2, VTH3) to create multiple switching stages. By changing the threshold voltage parameter across different transistors, the circuit can detect and respond to small voltage differences that would be below the threshold of a single diode-based circuit, thereby improving both resolution and reliability.

The patent combines multiple PMOS transistors with different threshold voltages and weak pull-down devices into a unified bulk voltage switching circuit. The transistors are connected in parallel with their sources connected to different voltage inputs (VCC, VSPAD) and drains connected to the bulk output terminal. This merging approach allows the circuit to achieve high reliability through voltage comparison across multiple stages while maintaining a relatively compact structure.

The weak pull-down devices automatically activate when the bulk voltage exceeds the normal withstand voltage range, providing self-protection without requiring external control. The circuit uses its own internal components (PMOS transistors with different VTH values) to automatically switch and isolate excessive voltage, making the circuit self-regulating and reducing the need for additional control logic.

The patent incorporates voltage isolation functionality into the bulk voltage switching circuit by using PMOS transistors with different threshold voltages that automatically activate at different voltage levels. When the bulk voltage approaches or exceeds the withstand voltage range, the appropriate transistor switches to isolate the excessive voltage before it can cause breakdown. This preliminary protective action occurs automatically without requiring external detection or intervention.

The PMOS transistors with different threshold voltages act as intermediaries between the power supply voltage inputs and the bulk output terminal. These transistors selectively conduct or block voltage based on their threshold characteristics, providing gradual voltage isolation and protection. The weak pull-down devices serve as additional intermediaries to ensure the bulk voltage remains within safe limits by providing a discharge path when needed.