Display Output Circuit Gate Precharge for Fast Signal Switching
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Solution Overview
Problem
Existing output circuits for liquid crystal display devices face delays in switching between charging and discharging operations, leading to potential image quality deterioration and uneven display due to differences in supply voltage ranges between differential stages and output stages.
Innovation Solution
An output circuit configuration with a differential amplifier circuit, an output amplifier circuit, and a control circuit that includes a third transistor and switch, where the third supply voltage is set between the first and second supply voltages, and the control circuit ensures the control terminal is conductive during the initial part of the output period to prevent delays by returning gate voltages to stable states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the supply voltage range of the output stage is reduced to lower power consumption, then power consumption is reduced, but output signal delay occurs during high-speed switching
Solution Approach 1:
The control circuit performs preliminary action by pre-charging the gate electrode of the output transistor to a voltage close to the power supply voltage before the actual output switching occurs. This preliminary charging reduces the time required for the output transistor to switch states, thereby preventing output signal delay while maintaining the reduced supply voltage range for power consumption efficiency.
Solution Approach 2:
The control circuit acts as an intermediary between the differential amplifier circuit and the output stage. It receives the output signal from the differential amplifier, processes it by adding the preliminary charge to the gate electrode, and then drives the output transistor. This intermediary function allows the output stage to respond faster without requiring a larger supply voltage range.
2Productivity
If the gate voltage switching speed is increased for high-speed drive, then productivity is improved, but gate voltage instability occurs leading to inconsistent switching
Solution Approach 1:
The control circuit applies preliminary action by charging the gate electrode to a predetermined voltage level before the actual switching operation. This ensures that the gate voltage starts from a stable, known state, which enables consistent and reliable switching behavior at high speeds without voltage instability.
Solution Approach 2:
The control circuit dynamically changes the gate voltage parameters by applying a boost voltage that is higher than the normal operating voltage during the switching transition. This temporary parameter change allows the transistor to switch faster and more consistently, after which the voltage returns to the normal stable operating level.
Data Source
AI summary
An output circuit includes a differential amplifier circuit, an output amplifier circuit, a control circuit, input and output terminals, and first to third supply terminals applied with first to third supply voltages, respectively. The third supply voltage is set a voltage between the first and second supply voltages. The differential amplifier circuit differentially receives signals of the input and output terminals. The output amplifier circuit includes first and second transistors of different conduction type each other coupled in series between the first and third supply terminals via the output terminal, and having control terminals coupled to first and second output nodes of the differential amplifier circuit, respectively. The control circuit includes a third transistor and a switch, and controls the third transistor being in a diode coupling mode between the first supply terminal and the control terminal of the first transistor for a given period of the output period.