Comparator Unit Gating for Low-Dark-Current Display Driving
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Solution Overview
Problem
In LED and organic electroluminescence displays, the high number of comparator circuits required for variable constant current driving leads to significant dark current and power consumption, especially in full-HD full-color displays.
Innovation Solution
A comparator unit is introduced that includes a comparison section to compare a control pulse with an electric potential based on a signal voltage and a control section to control the operation and non-operation of the comparison section, reducing dark current by allowing the comparison section to operate only when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a comparator circuit is provided in one pixel for each of about six million pixels in a full-HD full color display, then light emission control is achieved, but dark current of about 6 amperes flows in the entire display leading to large power consumption
Solution Approach 1:
The display pixels are divided into two groups (first pixel group and second pixel group) that are driven alternately. By segmenting the pixel array and controlling different groups at different times, the number of simultaneously active comparator circuits is reduced from six million to a manageable fraction, thereby reducing total dark current while maintaining full-color display capability through sequential updating
Solution Approach 2:
The drive circuit performs periodic switching between two driving modes: a first driving mode for the first pixel group and a second driving mode for the second pixel group. This periodic alternation allows comparator circuits to be inactive for portions of the frame period, reducing their dark current consumption while still achieving complete refresh of all pixels through time-multiplexed operation
2Productivity
If variable constant current driving method is used, then light emission duty is fixed, but blue shift occurs in spectrum wavelength causing variation in light-emission wavelength
Solution Approach 1:
The invention employs PWM (pulse-width modulation) driving that periodically switches the light emission on and off with varying duty cycles. This periodic control method adjusts the effective light output by changing the proportion of time the LED is active, rather than varying the current magnitude, thereby avoiding blue shift and maintaining stable light-emission wavelength while achieving variable brightness control
Solution Approach 2:
The invention changes the driving parameter from current magnitude (variable constant current) to time duration (PWM duty cycle). By controlling the width of current pulses rather than their amplitude, the system achieves variable light emission without causing spectral blue shift, thus maintaining wavelength stability while enabling brightness control
Data Source
AI summary
A comparator unit includes: a comparison section configured to compare a control pulse with an electric potential based on a signal voltage; and a control section configured to control, based on the control pulse, operation and non-operation of the comparison section.