Display DAC Differential Amplifier for Rail-to-Rail Gradation
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Solution Overview
Problem
Existing digital-to-analog converters in display devices face challenges in increasing the number of gradations while maintaining a manageable circuit size, as adding more reference voltages to enhance gradation levels leads to increased chip size and manufacturing costs.
Innovation Solution
A digital-to-analog converter design that includes a decoder selecting two voltages with overlap from a plurality of reference voltages and a differential amplifier circuit with both N-channel and P-channel differential stages, allowing operation over the entire power supply voltage range without significantly increasing circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the number of reference voltages is increased to increase the number of gradations, then the number of voltage levels increases, but the chip size increases
Solution Approach 1:
The patent divides the reference voltage generation into multiple segments using different conductivity types. Specifically, it uses first differential stages with first conductivity type transistors and second differential stages with second conductivity type transistors, each handling different voltage ranges. This segmentation allows the circuit to achieve multiple gradation levels without requiring a proportional increase in the number of reference voltages, thereby reducing chip size while maintaining high precision.
Solution Approach 2:
The patent changes the conductivity type parameter of transistors to expand the operational voltage range. By using both first conductivity type (e.g., N-channel) and second conductivity type (e.g., P-channel) transistors in differential stages, the circuit can operate across the entire power supply voltage range (rail-to-rail operation). This parameter change enables the generation of multiple gradation levels without increasing the number of reference voltages, thus avoiding chip size expansion.
2Manufacturing precision
If the number of reference voltages is increased to increase the number of gradations, then the number of voltage levels increases, but the manufacturing cost increases
Solution Approach 1:
The patent segments the differential amplification function into multiple stages with different conductivity types. This segmentation allows the circuit to achieve high-resolution gradation conversion using a limited set of reference voltages, reducing the complexity of the reference voltage generation circuitry and thereby lowering manufacturing costs while maintaining high manufacturing precision.
Solution Approach 2:
The patent makes the differential amplifier circuit multi-functional by using both first and second conductivity type transistors. This universal design allows the same circuit architecture to handle the entire voltage range and generate multiple gradation levels, eliminating the need for separate circuits for different voltage ranges and reducing overall manufacturing cost.
3Device complexity
If a single conductivity type is used in differential stages, then the circuit is simple, but the operation range is limited below threshold voltage
Solution Approach 1:
The patent changes the conductivity type parameter of transistors in different differential stages. By using first conductivity type transistors in first differential stages and second conductivity type transistors in second differential stages, the circuit achieves rail-to-rail operation capability. This parameter change allows the circuit to operate across the entire power supply voltage range, including regions below the threshold voltage of single conductivity type transistors, thereby expanding the operation range while maintaining reasonable circuit simplicity.
4Adaptability or versatility
If multiple conductivity types are used in differential stages, then the operation range expands to full power supply voltage, but the circuit area increases
Solution Approach 1:
The patent segments the differential amplification function into multiple stages with different conductivity types, where each stage handles a specific voltage range. This segmentation allows efficient use of circuit area by activating only the appropriate stages for given input voltages, achieving rail-to-rail operation without proportionally increasing the total circuit area.
Solution Approach 2:
The patent merges first differential stages with first conductivity type transistors and second differential stages with second conductivity type transistors into a unified differential amplifier circuit. This merging allows the circuit to achieve full power supply voltage operation while sharing common circuit resources such as current sources and output stages, thereby minimizing the increase in circuit area.
Data Source
AI summary
The differential amplifier circuit includes: first conductivity type first to Nth differential stages each causing a current corresponding to the first or second voltage received at the non-inverting input terminal to flow to a first node and a current corresponding to the output voltage signal received at the inverting input terminal to a second node; a second conductivity type differential stage receiving one of the first and second voltages at the non-inverting input terminal and receiving the output voltage signal at the inverting input terminal, and being activated when the digital data value is within a predetermined range to cause a current corresponding to the one voltage to flow to a third node and a current corresponding to the output voltage signal to a fourth node; and an output amplification stage generating the output voltage signal based on the currents respectively flowing to the first to fourth nodes.