Display DAC Differential Pair Biasing for Low Output Error
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Solution Overview
Problem
Existing digital-to-analog converters in display devices face challenges with increased output errors due to large voltage differences between reference voltages, leading to inaccuracies in analog output voltages, which are exacerbated by reduced chip size and manufacturing costs.
Innovation Solution
A digital-to-analog converter design that includes a differential amplifier with Kth-power of 2 differential pairs, a decoder, and a tail current control circuit to adjust current ratios, ensuring accurate output voltages by offsetting errors through tailored current distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of reference voltages is increased to increase the number of gradations, then the luminance level representation capability is improved, but the wiring region and number of switch elements increase, leading to increased chip size and manufacturing cost
Solution Approach 1:
The patent combines multiple reference voltage selection functions into a single differential amplifier circuit. Instead of using separate switch elements for each reference voltage selection, the invention uses a unified differential amplifier that can select and output appropriate voltage levels based on digital input signals, thereby reducing the number of discrete components and wiring regions while maintaining multi-gradation capability
Solution Approach 2:
The invention changes the operating parameters of the differential amplifier, specifically setting the tail current ratio to 1.06, to optimize the linearity and accuracy of voltage output. This parameter optimization allows the circuit to achieve high precision luminance representation without requiring additional components, thus resolving the contradiction between precision and chip size
2Use of energy by moving object
If the voltage difference between reference voltages is increased to expand dynamic range, then the output voltage range is improved, but the output error increases due to reduced linearity
Solution Approach 1:
The patent implements a feedback mechanism where the output voltage is fed back to the inverting input terminal of the differential amplifier. This negative feedback configuration allows the circuit to automatically adjust and maintain linearity across a wide voltage range, compensating for the non-linear effects that would otherwise occur with large voltage differences between reference voltages
Solution Approach 2:
The invention optimizes the tail current ratio parameter to 1.06 to enhance the linearity of the differential amplifier's transfer characteristic. This parameter adjustment ensures that even with large voltage differences between reference voltages, the output error remains minimal, thus expanding the dynamic range while maintaining high output voltage accuracy
3Ease of manufacture
If the chip size is reduced to lower manufacturing cost, then the manufacturing cost is improved, but the wiring region and number of switch elements must be reduced, which limits the number of reference voltages
Solution Approach 1:
The differential amplifier circuit is designed to perform multiple functions: it serves as both a voltage selector and an output buffer, and can generate multiple output voltage levels from a limited set of reference voltages. This multi-functionality allows the circuit to maintain high adaptability for different luminance requirements while using minimal components, thus reducing chip size and manufacturing cost
Solution Approach 2:
By optimizing the tail current ratio to 1.06, the invention enhances the precision and linearity of the differential amplifier, allowing it to accurately represent multiple luminance gradations even with a reduced number of physical reference voltages. This parameter optimization enables the circuit to achieve high versatility in luminance control without increasing chip size
Data Source
AI summary
The disclosure includes a differential amplifier and a first decoder that distributes and supplies a first or a second voltage to each of a plurality of input terminals based on digital data. The differential amplifier includes a Kth-power of 2 pieces of differential pairs each driven by an individually received tail current, and a tail current control circuit that individually supplies the tail current to the Kth-power of 2 pieces of the differential pairs. The tail current control circuit sets a current ratio of the tail current flowing through of two respective differential pairs among the Kth-power of 2 pieces of the differential pairs to be larger than a current ratio of the tail current flowing through other respective differential pairs excluding the two differential pairs.