Display Data Driver Output Circuit for Symmetric Slew Control
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Solution Overview
Problem
Current output circuits for high-speed data drivers in display devices face challenges in achieving symmetric slew rate during charging and discharging, leading to increased power consumption and heat generation, while also struggling with through currents due to capacitive coupling in phase compensation capacitances.
Innovation Solution
The proposed output circuit includes a differential input stage, an output amplifier stage, and a current control circuit that uses a single conductivity type differential pair, with current control circuits that adjust current sources to ensure symmetric voltage waveforms during charging and discharging, and phase compensation capacitances to stabilize output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed operation is implemented in output circuits, then data line driving speed is improved, but power consumption increases due to through currents caused by capacitive coupling
Solution Approach 1:
The patent converts the harmful through current caused by capacitive coupling into a beneficial effect by intentionally introducing a compensation capacitor that generates an equal and opposite current. This compensation current cancels the harmful through current, allowing high-speed operation without the associated power consumption penalty. The harmful capacitive coupling effect is thus transformed into a controllable parameter that can be compensated for.
Solution Approach 2:
The patent introduces a compensation capacitor as an intermediary element between the output terminal and ground. This compensation capacitor acts as a mediator that generates a compensating current to offset the harmful through current. By inserting this intermediate component, the system achieves high-speed operation while maintaining low power consumption, as the compensation capacitor isolates and neutralizes the harmful effect of capacitive coupling.
2Device complexity
If single conductivity type differential pairs are used, then device complexity is reduced, but symmetrical output voltage waveforms cannot be achieved
Solution Approach 1:
The patent deliberately introduces asymmetry through the compensation capacitor to counterbalance the inherent asymmetry in single conductivity type differential pairs. While the differential pair itself remains asymmetric (using only N-type or only P-type transistors), the compensation capacitor creates a symmetric current distribution that results in symmetrical output voltage waveforms. This controlled asymmetry allows the system to maintain simplicity while achieving waveform symmetry.
Solution Approach 2:
The patent achieves symmetrical output waveforms by adjusting the parameter of the compensation capacitor (its capacitance value) to match the total capacitive coupling effect of the differential pair. By changing this parameter to an optimal value, the system transforms the asymmetric behavior of single conductivity type differential pairs into symmetric output characteristics, maintaining device simplicity while achieving waveform symmetry.
3Use of energy by moving object
If through current is reduced, then power consumption decreases, but high-speed operation becomes difficult to achieve
Solution Approach 1:
The patent converts the harmful through current into a beneficial compensation mechanism. By introducing a compensation capacitor that generates an equal and opposite current, the system eliminates the power-consuming through current while simultaneously enabling high-speed operation. The compensation capacitor transforms the limitation into an opportunity to achieve both low power consumption and high speed performance.
Solution Approach 2:
The compensation capacitor creates a feedback mechanism where the output voltage change is fed back through the capacitor to generate a compensating current. This feedback current opposes and cancels the harmful through current, allowing the system to maintain low power consumption while achieving high-speed operation. The feedback loop continuously adjusts the compensating current to match the through current, ensuring minimal power consumption at high speeds.
Data Source
AI summary
An output circuit includes a differential input stage, an output amplifier stage, a current control circuit; an input terminal, an output terminal. The current control circuit includes a first circuit that includes a second current source connected between a first power supply terminal and the second current mirror, and exercises control of switching between activating the second current source to couple a current from the second current source to a current on an input side of the first current mirror, and deactivating the second current source, depending on whether or not the input voltage is higher by more than a first preset value than the output voltage; and a second circuit that includes a third current source connected between the second power supply terminal and the first current mirror, and exercises control of switching between activating the third current source to couple a current from the third current source to a current on an input side of the second current mirror, and deactivating the third current source, depending on whether or not the input voltage is lower by more than a second preset value than the output voltage.