Output Transistor Back-Gate Protection for Breakdown and Chip Area
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Solution Overview
Problem
Existing semiconductor devices with output-stage circuits require large transistors to meet breakdown voltage specifications, leading to increased chip size.
Innovation Solution
Incorporating a P-type output transistor with a voltage-breakdown protecting portion that applies power supply voltage to the back gate or disconnects the signal transmitting portion when the external connection pad voltage exceeds the power supply voltage, allowing for smaller transistors in the signal transmitting and voltage-breakdown protecting portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large size transistors are used in the output-stage circuit to satisfy breakdown voltage specification, then the breakdown voltage specification is satisfied, but the chip size becomes large
Solution Approach 1:
The patent divides the transistor into two separate components: a first transistor in the signal transmitting portion and a second transistor in the voltage-breakdown protecting portion. This segmentation allows each transistor to be optimized for its specific function, with the first transistor handling signal transmission and the second transistor providing breakdown protection, thereby reducing the overall chip area while maintaining reliability
Solution Approach 2:
The patent introduces a back gate as an intermediary element between the power supply voltage and the main transistor structure. By applying power supply voltage to the back gate of the first transistor through the second transistor, the system achieves breakdown voltage protection without requiring the main signal path transistor to be oversized, thus resolving the area-reliability contradiction
Data Source
AI summary
A semiconductor device of the present invention includes: a P-type output transistor configured to have a source to which a power supply voltage is applied, and a drain connected to an external connection pad; a gate wiring configured to be connected to a gate of the output transistor; a signal transmitting portion configured to transmit an input signal to the gate wiring; and a voltage-breakdown protecting portion configured to apply the power supply voltage to a back gate of the output transistor if a voltage on the external connection pad is equal to or lower than the power supply voltage, or the voltage-breakdown protecting portion bringing the signal transmitting portion into a disconnection state and applies the voltage on the external connection pad to the gate and the back gate of the output transistor if the voltage applied on the external connection pad is higher than the power supply voltage.