Gamma Amplifier Offset Trimming Without Flicker or High Current
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Solution Overview
Problem
Existing gamma amplifiers in display driving circuits suffer from offset voltage issues due to design and process variations, leading to inefficiencies and increased current consumption, with chopping and auto-zero methods causing flicker and size constraints.
Innovation Solution
An offset compensating circuit using a trimming method, comprising an input stage with multiplexers and current mirrors, and an amplification stage with polarity-changing multiplexers, to effectively compensate for gamma amplifier offsets while minimizing area and current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chopping method is used to compensate for gamma amplifier offset, then offset compensation is achieved, but flicker phenomenon occurs on the display
Solution Approach 1:
The patent applies preliminary action by measuring and compensating for the offset voltage during a test period before normal display operation. The offset compensation circuit measures the offset voltage of the gamma amplifier in advance (during test periods when the display is not actively showing content) and stores the measured value. During normal operation, the pre-measured offset compensation value is applied, avoiding the need for continuous chopping that causes flicker. This resolves the contradiction by achieving offset compensation without the harmful flicker effect during active display.
2Measurement precision
If auto-zero method is used to compensate for gamma amplifier offset, then offset compensation is achieved, but the circuit size and current consumption increase
Solution Approach 1:
The patent extracts only the essential offset measurement and compensation functionality from the complex auto-zero circuitry. Instead of implementing a full auto-zero amplifier with its associated capacitors, switches, and feedback paths, the invention separates the offset measurement function into a dedicated test mode that uses simplified circuit paths. The offset is measured during test periods and stored, then applied during normal operation without requiring the continuous complex circuitry of auto-zero methods. This extraction of the core function while removing unnecessary circuit elements reduces the overall circuit size while maintaining offset compensation accuracy.
Solution Approach 2:
The patent implements periodic action by performing offset measurement and compensation only during specific test periods rather than continuously. The display operating period is divided into normal display periods and test periods. During test periods, the offset measurement circuit is activated to measure and update the offset compensation value. During normal display periods, the pre-measured compensation value is applied without continuous measurement activity. This periodic operation reduces the active circuit elements at any given time, thereby reducing circuit size and current consumption while still achieving accurate offset compensation when needed.
3Measurement precision
If auto-zero method is used to compensate for gamma amplifier offset, then offset compensation is achieved, but current consumption increases
Solution Approach 1:
The patent implements periodic action by performing offset measurement and compensation only during specific test periods rather than continuously. The display operating period is divided into normal display periods and test periods. During test periods, the offset measurement circuit is activated to measure and update the offset compensation value. During normal display periods, the pre-measured compensation value is applied without continuous measurement activity. This periodic operation reduces the active circuit elements at any given time, thereby reducing circuit size and current consumption while still achieving accurate offset compensation when needed.
Solution Approach 2:
The patent extracts only the essential offset measurement and compensation functionality from the complex auto-zero circuitry. Instead of implementing a full auto-zero amplifier with its associated capacitors, switches, and feedback paths, the invention separates the offset measurement function into a dedicated test mode that uses simplified circuit paths. The offset is measured during test periods and stored, then applied during normal operation without requiring the continuous complex circuitry of auto-zero methods. This extraction of the core function while removing unnecessary circuit elements reduces the overall circuit size and current consumption while maintaining offset compensation accuracy.
Data Source
AI summary
Provided is an offset compensating circuit that includes: an input stage circuit with first and second input circuits, a first multiplexer configured to activate one of the first second input circuits, a second multiplexer configured to change a polarity of an offset, and an offset trimming circuit configured to compensate the offset; an amplification stage circuit with a first current mirror, a second current mirror and a third multiplexer configured to change the polarity of the offset; an output stage circuit configured to receive voltages generated from the first current mirror and the second current mirror; and a switch configured to control a path connected to the output stage circuit or the input stage circuit.