Depletion Transistor Gate Offset Circuit for Stable Bootstrap Operation
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Solution Overview
Problem
Display devices using transistors with the same conductivity type in driver circuits face issues with malfunction and transistor degradation due to the use of depletion transistors, which cannot be turned off at Vgs of 0 V, leading to bootstrap operation failures and high Vgs that promote transistor degradation.
Innovation Solution
A semiconductor device configuration that includes specific transistor arrangements and capacitors to generate offset signals, allowing depletion transistors to be turned off and reducing Vgs, thereby preventing malfunction and degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If depletion transistors are used in driver circuits, then device complexity is reduced, but reliability deteriorates due to inability to turn off at Vgs of 0V
Solution Approach 1:
A capacitor is introduced as an intermediary element to store charge and maintain the gate potential of the depletion transistor above the threshold level. This capacitor acts as a mediator that prevents the gate voltage from dropping to 0V, ensuring the transistor can be properly turned off while maintaining circuit reliability.
Solution Approach 2:
The gate potential parameter is actively controlled and changed through the capacitor's charge storage function. By maintaining the gate potential above the threshold voltage, the transistor's operational state can be properly controlled, transforming the inability to turn off at 0V into a controllable parameter.
2Ease of manufacture
If depletion transistors are used to reduce device complexity, then manufacturing is simplified, but transistor degradation is accelerated due to high Vgs
Solution Approach 1:
The capacitor serves as a protective intermediary that limits the maximum gate-source voltage by storing charge. This prevents excessive Vgs from developing across the transistor, thereby reducing electrical stress and extending transistor lifespan while maintaining the simplified depletion transistor configuration.
Solution Approach 2:
The capacitor is positioned beforehand in the circuit to cushion against voltage spikes and prevent excessive Vgs from reaching the transistor. This prior protective measure reduces electrical stress before degradation can occur, extending the transistor's operational life.
3Productivity
If the gate of transistor M1 is made into a floating gate for bootstrap operation, then signal output capability is improved, but device complexity increases
Solution Approach 1:
The capacitor acts as an intermediary that enables the floating gate functionality without requiring complex additional circuitry. By using the capacitor's charge storage capability, the bootstrap operation is achieved through a simple gate connection, maintaining productivity while minimizing complexity.
Solution Approach 2:
The capacitor serves multiple functions: it enables the floating gate operation for signal output, maintains the gate potential above threshold, and protects against excessive Vgs. This multi-functionality achieves improved signal output capability without proportionally increasing 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 ensures stable operation of depletion transistors by turning them off and reducing drain current, preventing circuit malfunction and suppressing transistor degradation.
Implementation Method 1
a capacitor C1. In Patent Document 1, in the case where a signal at high level is output as a signal OUT, a gate of the transistor M1 is made into a floating gate, and a bootstrap operation in which the potential of the gate of the transistor M1 is increased to be higher than a potential VDD by using capacitive coupling of the capacitor C1
Implementation Method 2
a bootstrap operation in which the potential of the gate of the transistor M1 is increased to be higher than a potential VDD by using capacitive coupling of the capacitor C1
Data Source
AI summary
Provided is a semiconductor device which can operate stably even in the case where a transistor thereof is a depletion transistor. The semiconductor device includes a first transistor for supplying a first potential to a first wiring, a second transistor for supplying a second potential to the first wiring, a third transistor for supplying a third potential at which the first transistor is turned on to a gate of the first transistor and stopping supplying the third potential, a fourth transistor for supplying the second potential to the gate of the first transistor, and a first circuit for generating a second signal obtained by offsetting a first signal. The second signal is input to a gate of the fourth transistor. The potential of a low level of the second signal is lower than the second potential.