LED Driver Circuit Segmentation for Exponential Brightness Control
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Solution Overview
Problem
Existing driver circuits for light emitting units face challenges in efficiently and precisely implementing the exponential relationship between brightness codes and driver signals to control the brightness level of LEDs.
Innovation Solution
A driver circuit comprising a digital-to-analog converter (DAC) stage to generate an intermediate signal and a gain stage to amplify it, allowing for precise control of the driver current based on the brightness code, with a programmable gain stage that implements an exponential gain curve using auxiliary branches and resistive elements to match the target relationship.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional driver circuit uses a linear relationship between brightness code and driver signal, then the circuit design is simple, but the brightness control precision is insufficient to match the exponential perception of human vision
Solution Approach 1:
The driver circuit is divided into two functional stages: a DAC stage for linear digital-to-analog conversion and a gain stage for exponential amplification. This segmentation allows each stage to perform its function optimally while maintaining overall system precision for exponential brightness control.
Solution Approach 2:
An intermediate analog signal is introduced between the digital brightness code and the final driver current. The DAC converts the digital code to this intermediate analog signal, which then passes through the gain stage to achieve the final exponential driver current, enabling precise brightness control through this intermediary representation.
2Duration of action of moving object
If the driver circuit uses a high headroom voltage design, then the circuit has sufficient voltage margin for operation, but the dynamic range and resolution of the driver current are reduced
Solution Approach 1:
The circuit dynamically adjusts the gain parameter in the gain stage based on the brightness code value. By changing the gain parameter adaptively, the circuit achieves exponential driver current output with high dynamic range while maintaining low headroom voltage operation, as the gain adjustment compensates for the reduced voltage margin.
3Manufacturing precision
If the driver circuit implements a precise exponential relationship, then the brightness control accuracy is high, but the circuit complexity and component requirements increase
Solution Approach 1:
The exponential relationship is achieved by segmenting the function across two stages: linear DAC conversion followed by exponential gain amplification. This segmentation allows the use of standard linear DAC components while achieving precise exponential control through the subsequent gain stage, reducing the need for complex custom exponential DAC design.
Solution Approach 2:
The gain stage uses dynamic gain adjustment based on the brightness code to implement the exponential relationship. By making the gain parameter variable rather than fixed, the circuit achieves precise exponential control using standard components, avoiding the need for complex fixed exponential conversion circuits.
Data Source
AI summary
A driver circuit for providing a driver current for operating a light emitting unit at a brightness level corresponding to a value of a brightness code. The driver circuit includes a digital-to-analog converter, DAC, stage configured to generate an intermediate signal in dependence of the value of the brightness code. Furthermore, the driver circuit includes a gain stage configured to amplify the intermediate signal in dependence of the value of the brightness code to provide the driver current.