Output Buffer Bias Modulation for Low-EMI Display Driving
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Solution Overview
Problem
Existing high-speed drive output buffer circuits face challenges in reducing electromagnetic interference (EMI) and power consumption due to transient through-currents between transistors, while also maintaining optimal current driving capability and pulse waveform quality.
Innovation Solution
The output buffer circuit incorporates a bias part with a bias modulation part that adjusts the bias voltage based on setting signals, allowing for precise control of transistor states and current driving capability, thereby minimizing through-currents and EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the current flowing in the current source of the pre-buffer part is reduced to curb through-current and reduce EMI, then EMI and power consumption are reduced, but the time for transistor switching from OFF to ON becomes longer, causing gradual voltage change and deterioration in current driving capability
Solution Approach 1:
The patent applies dynamics by making the current source current variable rather than fixed. The current value is dynamically adjusted based on the operating state - using a smaller current value when curbing through-current is prioritized, and a larger current value when fast switching is required. This is achieved through control circuitry that modifies the current source parameters in response to system conditions, allowing the output buffer to adapt between EMI reduction mode and high-speed driving mode.
2Speed
If a high-speed drive output buffer is used to achieve fast switching, then switching speed is improved, but transient through-current flows between transistors causing EMI and increased power consumption
Solution Approach 1:
The patent applies preliminary action by introducing a pre-buffer stage before the main output buffer. This pre-buffer performs preliminary switching actions that prepare the transistors for the subsequent main switching event. By pre-charging or pre-discharging capacitor elements in the pre-buffer stage, the main transistors can switch more quickly without experiencing large transient through-currents, as the voltage transitions are already partially completed in the pre-buffer stage.
Solution Approach 2:
The pre-buffer acts as an intermediary between the input signal and the main output buffer transistors. It mediates the switching process by handling the initial voltage transitions and current flows, thereby protecting the main output stage from direct exposure to large transient currents. The pre-buffer absorbs the harmful through-current effects while enabling the main buffer to operate at high speed with reduced EMI.
Data Source
AI summary
An output buffer circuit includes a first transistor supplying a first high-voltage power supply voltage in a case of being ON in response to a voltage of an input signal received through a gate; a second transistor supplying a second high-voltage power supply voltage in the case of being ON in response to a voltage of the input signal received through a gate; an output control part that shifts a transistor, of the first and second transistors, being ON to OFF at a time of voltage change of the input signal by changing the voltage in the gate thereof, and turns a transistor being OFF to ON by changing the voltage in the gate thereof at a rate of change based on a current value controlled by a bias voltage, and a bias modulation part that sets a voltage value of the bias voltage to a designated voltage value.