Gate Driver Back Bias Circuit Reduces Leakage Current
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Solution Overview
Problem
In display devices, N-type oxide thin film transistors (TFTs) with negative threshold voltage exhibit increased leakage current, leading to distorted output waveforms and elevated power consumption, which affects reliability and efficiency.
Innovation Solution
A gate driver with a back bias circuit is implemented, applying a back gate bias voltage lower than the source voltage to the light shielding layers of TFTs during their off-period, shifting the negative threshold voltage to positive and reducing leakage current and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If N-type oxide TFT with negative threshold voltage is used, then device performance is improved, but leakage current increases
Solution Approach 1:
The patent applies parameter changes by introducing a back gate bias voltage that shifts the threshold voltage from negative to positive. This modifies the electrical parameter (threshold voltage) of the TFT to eliminate the harmful leakage current while preserving the device's functional performance. The back gate bias circuit dynamically adjusts the threshold voltage based on operational requirements.
2Object-generated harmful factors
If leakage current is increased, then output waveform distortion occurs, but reliability deteriorates
Solution Approach 1:
The patent implements preliminary anti-action by proactively applying a back gate bias voltage to counteract the negative threshold voltage effect before it causes harmful leakage current and waveform distortion. This preventive measure ensures that the threshold voltage remains positive throughout operation, maintaining reliable output waveforms and preventing reliability issues before they occur.
3Object-generated harmful factors
If leakage current increases, then power consumption increases, but energy efficiency decreases
Solution Approach 1:
The patent uses parameter changes to modify the threshold voltage from negative to positive through the back gate bias circuit. This parameter modification eliminates the leakage current pathway, directly reducing power consumption and improving energy efficiency. The circuit dynamically adjusts the threshold voltage to minimize energy waste while maintaining operational requirements.
Data Source
AI summary
A display device having a gate driver, which may reduce a leakage current of a TFT and power consumption, is disclosed. Each stage of the gate driver comprises an output portion including a pull-up transistor outputting a corresponding clock of a plurality of clocks as a gate signal in response to control of a Q node, and a pull-down transistor outputting a gate-off voltage as an off-voltage of a gate signal in response to control of a QB node; a controller charging and discharging the Q node and charging and discharging the QB node to be in an opposite state of the Q node; and a back bias circuit having a back bias node capacitance-coupled with the Q node and generating a back gate bias voltage to apply the back gate bias voltage to the back bias node for an off-period of the Q node, wherein the back bias circuit may apply the back gate bias voltage to light shielding layers of some transistors, which are turned off for the off-period of the Q node, among transistors constituting the output portion and the controller, through the back bias node, thereby reducing or minimizing a leakage current of the corresponding transistors.