Segmented DAC Reference Circuit for Compact LED Driver Dimming
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Solution Overview
Problem
Existing LED drivers require a large physical layout area due to the high number of circuit components needed for high-resolution brightness control, leading to increased size and cost, especially when integrating multiple local dimming zones for improved power efficiency and contrast ratio.
Innovation Solution
The proposed solution involves segmenting the digital-to-analog converter (DAC) into a thermometer-type sub-DAC and a switchable resistor sub-DAC, reducing the total number of circuit components and simplifying the decoder design, thereby minimizing the area occupied by resistors and decoder circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermometer-type DAC is used for high-resolution brightness control, then brightness control resolution is improved, but the physical layout area of the LED driver increases due to the large number of circuit components
Solution Approach 1:
The patent divides the thermometer-type DAC into multiple sub-DACs, each handling a portion of the brightness control resolution. This segmentation reduces the number of circuit components in each sub-DAC while maintaining the overall high-resolution capability when combined, thereby reducing the total physical layout area required.
2Use of energy by moving object
If the number of local dimming zones is increased for improved power efficiency and contrast ratio, then power efficiency and image quality are improved, but the number of circuit components and physical layout area increase
Solution Approach 1:
The patent applies segmentation to the DAC structure to enable support for multiple local dimming zones. By using multiple sub-DACs with reduced component counts, the system can handle the increased control requirements for multiple zones without proportionally increasing the overall circuit area, thus improving power efficiency and contrast ratio while controlling layout area.
3Measurement precision
If a B-bit thermometer-type DAC is used for fine resolution brightness control, then brightness control resolution is improved, but the number of circuit components doubles or quadruples for every additional bit
Solution Approach 1:
The patent segments the B-bit thermometer-type DAC into multiple sub-DACs, where each sub-DAC handles a portion of the bits. This reduces the number of circuit components in each individual sub-DAC, avoiding the exponential increase that would occur with a single full-resolution thermometer-type DAC, while maintaining the overall B-bit resolution capability.
4Measurement precision
If poly-silicon resistors are used to achieve good matching property for DAC linearity, then DAC linearity performance is improved, but the physical layout area increases due to the need for many parallel-connected unit resistors
Solution Approach 1:
The patent segments the resistor network into multiple sub-DACs, each with fewer resistors. This segmentation maintains the matching property and linearity performance through proper resistor design in each sub-DAC while reducing the total layout area by distributing the resistors across multiple smaller units rather than requiring all resistors in a single large network.
Data Source
AI summary
A digital-to-analog converter (DAC) for generating an output voltage according to an input code includes a first-type and a second-type sub-DAC's connected in series. The first-type sub-DAC includes a first resistor string and plural first switches, and receives a reference current to determine a first voltage drop. The first switches are controlled by a first portion of the input code to determine a voltage division of the first voltage drop. The second-type sub-DAC includes a second resistor string and plural second switches. The second switches are controlled by a second portion of the input code to determine a portion of the second resistor string to receive the reference current, wherein the portion of the second resistor string and the reference current determines a second voltage drop. The output voltage includes a sum of the second voltage drop and the voltage division of the first voltage drop.