Differential DAC Circuit With Tail Current Control for Smaller Drivers
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Solution Overview
Problem
Existing digital-to-analog converters face challenges in reducing chip size and manufacturing costs due to the increase in the number of reference voltages and switching elements required for higher grayscale levels, which is exacerbated by the increase in differential pairs and decoder elements when increasing the number of voltage levels.
Innovation Solution
A digital-to-analog conversion circuit with a differential amplifier having multiple input terminals and a tail current control circuit that distributes and supplies voltages to these terminals based on digital data, allowing for increased voltage levels with a reduced number of differential pairs, thereby controlling tail current ratios to achieve area reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of reference voltages is increased to achieve higher grayscale levels, then the luminance level expression capability is improved, but the wiring area and number of switching elements increase, leading to increased chip size
Solution Approach 1:
The patent merges the functions of multiple reference voltage generation circuits into a single differential amplifier that can generate multiple output voltages by dividing two reference voltages with predetermined weights. This consolidation reduces the number of separate reference voltage generation circuits from multiple independent circuits to one shared circuit, thereby reducing wiring area and switching elements while maintaining the capability to express multiple grayscale levels.
Solution Approach 2:
The differential amplifier is designed with multi-functionality to serve as both a reference voltage generation circuit and an output driver. By configuring the differential amplifier to receive two reference voltages and output multiple divided voltage levels (e.g., Vref/2, Vref/4, 3Vref/4) through controlled switching of differential pairs, it eliminates the need for separate reference voltage ladders, reducing overall circuit complexity and chip area.
2Measurement precision
If the number of differential pairs is increased to achieve higher voltage levels, then the voltage level precision is improved, but the number of decoder elements increases, leading to increased device complexity
Solution Approach 1:
The patent employs dynamic control of the differential amplifier's tail current based on the most significant bit (MSB) of the input digital signal. When the MSB is high, the tail current is set to a first value; when low, it is set to a second value. This dynamic current adjustment enables the same differential pair structure to produce different voltage divisions (e.g., 1/2, 1/4, 3/4) without requiring additional differential pairs or complex decoder logic, thereby reducing device complexity while maintaining voltage level precision.
3Measurement precision
If the number of reference voltages is increased to achieve higher grayscale levels, then the luminance level expression capability is improved, but the number of switching elements increases, leading to increased manufacturing cost
Solution Approach 1:
The patent merges the functions of multiple reference voltage generation circuits into a single differential amplifier that can generate multiple output voltages by dividing two reference voltages with predetermined weights. This consolidation reduces the number of separate reference voltage generation circuits from multiple independent circuits to one shared circuit, thereby reducing wiring area and switching elements while maintaining the capability to express multiple grayscale levels.
Solution Approach 2:
The patent changes the operational parameters of the differential amplifier by dynamically adjusting the tail current based on the MSB input. This parameter change allows the same hardware structure to produce different voltage division ratios without requiring additional switching elements or reference voltage lines, thereby reducing manufacturing complexity and cost while maintaining high grayscale expression capability.
Data Source
AI summary
A digital-to-analog conversion circuit includes a differential amplifier outputting 2N voltage levels dividing first and second voltages and a decoder distributing and supplying one of first and second voltages to a plurality of input terminals of the differential amplifier on the basis of digital data of N bits, and the differential amplifier includes 2K differential pairs including an inverting input terminal to which an output voltage is commonly input and a non-inverting input terminal to which one of voltages received by the plurality of input terminals is input and having output pairs commonly connected with each other and a tail current control circuit individually controlling current ratios of tail currents supplied to the differential pairs on the basis of a predetermined bit of digital data, in which N is equal to or greater than 3, and K is a positive number less than N.