PWM Current Source Using Inverter Capacitance for Micro-LED Brightness
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Solution Overview
Problem
Current PWM circuits used in modern displays with high integration densities face limitations in achieving precise brightness gradations due to the inertia of light-emitting diodes and space constraints, particularly in micro-LEDs with edge lengths smaller than 70 μm.
Innovation Solution
A PWM controlled current source is developed using the SRAM concept, where an inverter circuit with capacitances conditions the switching operation, allowing for fine-tuned pulse width modulation by interacting with a voltage-to-current converter, enabling precise control of current flow to optoelectronic components with minimal area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PWM circuits are used to control light emitting diodes, then brightness can be adjusted, but the inertia of the light emitting diode prevents precise brightness gradations
Solution Approach 1:
The patent applies preliminary action by pre-charging capacitors during a first time period before the actual PWM switching occurs. This allows the capacitors to be ready to quickly discharge and control the current source, overcoming the inertia of the light emitting diode and enabling precise brightness gradations without being limited by the LED's response time.
2Productivity
If integration density is increased in modern displays, then more pixels can be accommodated, but space for current sources and PWM circuits becomes critically limited
Solution Approach 1:
The patent merges the PWM circuit functionality with the current source control by using shared capacitors and control signals. The same capacitors that store voltage are used to control the current source switching, eliminating the need for separate PWM generation circuits and reducing the overall area required for each pixel element.
Solution Approach 2:
The patent implements multi-functionality by designing capacitors that serve multiple purposes: they store voltage for current source control, generate PWM signals, and regulate current flow. This universal approach allows a single component to perform multiple functions that would traditionally require separate circuits, thereby reducing the area required per pixel.
3Illumination intensity
If pulse width modulation frequency is increased to avoid visible switching, then brightness control is achieved, but the switching process becomes noticeable to sensors
Solution Approach 1:
The patent employs periodic action through capacitor charging and discharging cycles that occur at controlled frequencies. The capacitors are charged during a first time period and discharged during a second time period, creating periodic current pulses that control the light emitting diode brightness. This periodic operation allows the switching to occur at frequencies above human visual detection while maintaining precise brightness control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for high integration density PWM modulation with pulse lengths in the range of 0.1 μs to 10 μs, achieving precise brightness control with low power consumption and small footprint, suitable for micro-LEDs and other optoelectronic components.
Implementation Method 1
The inverter circuit has a capacitance conditioned by elements of the circuit
Implementation Method 2
a voltage-to-current converter which generates a current derived from a modulation signal
Data Source
AI summary
A PWM controlled current source includes a selection input, a modulation input, a switchable current source which can be switched by means of a signal at a control terminal and whose current output is configured for connection to a load, and an inverter circuit including an input node and an output coupled to the control terminal. The inverter circuit has a capacitance conditioned by elements of the inverter circuit. A start signal can be supplied to the input node in dependence on a selection signal at the selection input, which controls the switchable current source via the inverter circuit. The PWM controlled current source also includes a voltage-to-current converter that generates a current derived from a modulation signal at the modulation input and supplies it to the input node. The supplied current disconnects the switchable current source after a time period predetermined by the conditioned capacitance.