Grayscale Voltage Generator Circuit Offset Reduction
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Solution Overview
Problem
Existing grayscale voltage generator circuits in display panels face issues with increased circuit area due to the number of switches, leading to higher parasitic capacitance and lower response speed, and are susceptible to offset voltages that can affect display quality.
Innovation Solution
A semiconductor device with a configuration that includes a first and second amplifier circuit, a selector circuit, and a current control circuit, which generates voltages and currents to minimize the impact of offset voltages and reduce circuit area by allocating only the upper-bit signal to a resistor string DAC, maintaining the correspondence between digital signals and analog outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of bits of digital signals is increased to achieve higher grayscale performance, then the grayscale precision is improved, but the number of switches increases exponentially causing the circuit area to increase
Solution Approach 1:
The patent divides the N-bit digital signal into two parts: upper-bit signals and lower-bit signals. The upper-bit signals control a resistor string DAC while the lower-bit signals control current sources. This segmentation allows the circuit to achieve high grayscale precision without requiring an exponential number of switches, as each segment handles a portion of the bit resolution independently.
Solution Approach 2:
The patent transitions from a single-dimension switch-based DAC architecture to a two-dimension architecture combining voltage-based resistor string DAC for upper bits and current-based DAC for lower bits. This dimensional change in signal processing approach enables high precision grayscale generation with reduced switch count and circuit area.
2Measurement precision
If the number of switches is increased to support more digital signal bits, then the grayscale precision is improved, but the parasitic capacitance increases causing response speed to decrease
Solution Approach 1:
By segmenting the DAC into voltage-based and current-based portions, the patent reduces the number of switches required in the critical signal path. The upper-bit resistor string DAC uses fewer switches compared to a full N-bit switch-based DAC, thereby reducing parasitic capacitance and improving response speed while maintaining grayscale precision through the combined architecture.
3Measurement precision
If an amplifier circuit is used to generate output analog signal, then the grayscale voltage is improved, but the offset voltage of the amplifier circuit affects the output voltage causing display quality to deteriorate
Solution Approach 1:
The patent extracts the offset voltage issue from the amplifier circuit by using a differential amplifier configuration where two amplifiers process complementary signals. The offset voltages of the two amplifiers are subtracted from each other in the differential configuration, effectively canceling out the offset influence and improving display quality while maintaining grayscale voltage precision.
4Measurement precision
If a current DAC with high withstand voltage transistor is used, then the grayscale voltage generation is improved, but the circuit area increases due to the number of switches
Solution Approach 1:
The patent segments the DAC functionality between voltage-based resistor string DAC for upper bits and current-based DAC for lower bits. This segmentation allows the current DAC to use fewer switches with high withstand voltage transistors only where necessary, reducing the overall circuit area while maintaining grayscale voltage generation capability.
Data Source
AI summary
A grayscale voltage generator circuit that is less likely to be influenced by the offset voltage is provided. The grayscale voltage generator circuit is a semiconductor device that includes a D/A converter circuit, a first Gm amplifier, a second Gm amplifier, a current control circuit, an output buffer, and a selector circuit. The D/A converter circuit generates a first voltage and a second voltage from an upper bit of a digital signal. The current control circuit generates a first current from a lower bit of the digital signal and functions as a current source of the first Gm amplifier. The output buffer generates a third voltage from currents output from the first Gm amplifier and the second Gm amplifier. The third voltage is input to the second Gm amplifier. The selector circuit selects voltages that are to be input to the first Gm amplifier and the second Gm amplifier.