MOSFET Pad Leakage Control via Dynamic Gate Potential
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Solution Overview
Problem
Conventional ESD protection circuits using MOS-type protection devices suffer from leak currents due to floating gate and backgate potentials, leading to signal attenuation and increased current flow when signal potentials exceed or fall below the power supply voltage.
Innovation Solution
A semiconductor integrated circuit device with a pad connected to a power supply wiring through a first MOSFET, where the gate and backgate are common, and a second MOSFET with its gate connected to the pad and backgate of the first MOSFET, along with a potential control circuit that adjusts the gate and backgate potential based on the input signal, ensuring the MOSFET remains fully off to prevent leak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If the gate and backgate are left in a floating state to prevent signal attenuation, then signal transmission is improved, but leak currents increase when signal potentials exceed or fall below the power supply voltage
Solution Approach 1:
A potential control circuit is introduced as an intermediary between the floating gates/backgates and the signal source. This control circuit actively monitors the signal potential and adjusts the gate/backgate potentials accordingly, preventing both signal attenuation and leak currents by maintaining the MOSFET in a fully off state when signal potentials exceed or fall below the power supply voltage.
Solution Approach 2:
The potential control circuit implements a feedback mechanism where the signal potential is continuously monitored and used to adjust the gate and backgate potentials. When the signal potential exceeds or falls below the power supply voltage, the control circuit adjusts the gate/backgate potentials to ensure the MOSFET remains fully off, thereby preventing leak currents while maintaining signal integrity.
2Object-generated harmful factors
If the MOSFET is kept fully off to prevent leak currents, then current leakage is reduced, but signal transmission is blocked when signal potentials exceed power supply voltage
Solution Approach 1:
The gate and backgate potentials are made dynamic rather than fixed. The potential control circuit continuously adjusts the gate and backgate potentials based on the signal potential, allowing the MOSFET to transition between fully off (to prevent leak currents) and partially conductive (to allow signal transmission) states. This dynamic control resolves the contradiction by adapting the MOSFET's conduction state to the instantaneous signal conditions.
3Object-generated harmful factors
If a second MOSFET is added to control the gate potential, then leak current control is improved, but device complexity increases
Solution Approach 1:
The potential control circuit combines multiple control functions into a single integrated structure. The second MOSFET's gate is connected to the first MOSFET's gate and backgate, and the potential control circuit simultaneously controls both the gate and backgate potentials of the first MOSFET. This merging of control functions into a unified circuit structure achieves effective leak current control while minimizing the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces leak currents in MOSFETs connected between a pad and power supply wiring, even when signals have potentials higher or lower than the power supply voltage, by ensuring the MOSFETs remain fully turned off, thereby preventing signal attenuation and current leakage.
Implementation Method 1
the n-type MOSFET 101 performs a parasitic bipolar transistor operation because of the breakdown of the p-n junction between the drain and the backgate
Implementation Method 2
the breakdown of the p-n junction between the drain and the backgate
Implementation Method 3
the p-n junction between the drain and the backgate is forward-biased
Data Source
AI summary
To reduce the leak current in the MOSFET connected between the pad and the ground. There are provided a pad PAD for an input or output signal, an n-type MOSFET M1a connected between the pad PAD and the ground and having its gate terminal and backgate connected in common, and a potential control circuit 10 that controls a potential Vb of the gate terminal and the backgate of the n-type MOSFET M1a based on a potential Vin of the pad PAD. The potential control circuit 10 comprises n-type MOSFETs M2 and M3; the n-type MOSFET M1a has its gate terminal and backgate connected to backgates and drains of the n-type MOSFETs M2 and M3; the n-type MOSFET M2 has its source grounded and its gate terminal connected to the pad PAD via a resistance R; and the n-type MOSFET M3 has its source connected to the pad PAD and its gate terminal grounded.