Variable-Transconductance Differential Amplifier for Display DNL Control
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Solution Overview
Problem
Existing differential difference amplifier circuits in data drivers for display panels face challenges in achieving optimal display quality due to fixed transconductance, leading to predictable and undesirable differential nonlinearity (DNL) that can result in uneven brightness and darkness in display regions.
Innovation Solution
A differential difference amplifier circuit with variable transconductance is designed, incorporating a bias generation circuit that controls the magnitude of current sources and utilizes switches to modulate transconductance based on image data, randomizing the DNL curve for improved display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed transconductance differential pair is used, then the circuit structure is simple, but the differential nonlinearity (DNL) is predictable and causes uneven brightness in display regions
Solution Approach 1:
The patent applies dynamics by making the transconductance of the differential pair variable rather than fixed. A control circuit dynamically adjusts the transconductance value based on the input signal amplitude, randomizing the DNL curve to eliminate predictable brightness patterns in display regions while maintaining circuit simplicity.
2Object-affected harmful factors
If a variable transconductance differential pair is used, then the DNL curve is randomized for improved display quality, but the circuit complexity increases
Solution Approach 1:
The patent changes the transconductance parameter dynamically based on input signal conditions. By controlling the transconductance value according to signal amplitude, the system randomizes the DNL curve to improve display uniformity while managing circuit complexity through parameter modulation rather than structural complexity.
Solution Approach 2:
The patent implements feedback by using the input signal itself to control the transconductance value. The control circuit monitors the input signal amplitude and adjusts the differential pair's transconductance accordingly, creating a self-regulating system that randomizes DNL without requiring external complex control mechanisms.
3Object-affected harmful factors
If high-resolution DACs are used to improve display quality, then the display uniformity improves, but the hardware cost increases
Solution Approach 1:
Instead of using high-resolution DACs, the patent changes the transconductance parameter dynamically to achieve display uniformity. This parameter modulation approach provides the necessary precision for uniform brightness distribution without requiring expensive high-resolution digital-to-analog converters, thereby reducing hardware cost.
Data Source
AI summary
The differential difference amplifier circuit includes a differential input stage circuit, a loading stage circuit coupled to the differential input stage circuit, and an output stage circuit coupled to the loading stage circuit. The output stage circuit is configured to generate an output signal. The differential input stage circuit includes a first differential pair having a first transconductance and a second differential pair having a second transconductance. The first differential pair is biased by a first current source and receives a first input signal and the output signal. The second differential pair is biased by a second current source and receives a second input signal and the output signal. At least one of the first transconductance and the second transconductance is adjusted according to the image data.